# Electronic Products; Performance Standard for Diagnostic X-Ray Systems and Their Major Components

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URL: https://www.frixlaw.com/law-library/documents/fr%3A02-30550

## Record

- **Collection:** Federal Register
- **Document type:** Proposed Rule
- **Published:** December 10, 2002
- **Citation:** 67 FR 76056

## Text

DEPARTMENT OF HEALTH AND HUMAN SERVICES
Food and Drug Administration
21 CFR Part 1020
[Docket No. 01N-0275]
RIN 0910-AC34
Electronic Products; Performance Standard for Diagnostic X-Ray Systems and Their Major Components

AGENCY:

Food and Drug Administration, HHS.

ACTION:

Proposed rule.

SUMMARY:

The Food and Drug Administration (FDA) is proposing to amend the performance standard for diagnostic x-ray systems and their major components. The agency is taking this action to update the standard to account for changes in technology and use of radiographic and fluoroscopic systems as well as to fully utilize the currently accepted metric system of units in the standard. For clarity and ease of understanding, FDA is republishing the complete contents of the affected regulations. This action is being taken under the Federal Food, Drug, and Cosmetic Act (the act), as amended by the Safe Medical Devices Act of 1990 (SMDA).

DATES:

Submit written or electronic comments by April 9, 2003. See section III of this document for the proposed effective date of a final rule based on this document. Submit written comments on the information collection requirements by January 9, 2003.

ADDRESSES:

Submit written comments to the Dockets Management Branch (HFA-305), Food and Drug Administration, 5630 Fishers Lane, rm. 1061, Rockville, MD 20852. Submit electronic comments to http://www.fda.gov/dockets/ecomments. Submit written comments regarding the information collection requirements to the Office of Information and Regulatory Affairs, Office of Management and Budget (OMB), New Executive Office Bldg., 725 17th St., NW. rm. 10235, Washington, DC 20503, Attn: Desk Officer for FDA.

FOR FURTHER INFORMATION CONTACT:

Thomas B. Shope, Center for Devices and Radiological Health (HFZ-140), Food and Drug Administration, 9200 Corporate Blvd., Rockville, MD 20850, 301-443-3314, ext. 132.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Background

II. Proposed Amendments to the Performance Standard for Diagnostic X-Ray Systems and Their Major Components

A. Change in the Quantity Used to Describe X-Radiation From Exposure to Air Kerma

B. Clarification of Applicability of Requirements to Account for Technological Developments in Fluoroscopic X-Ray Systems Such as Digital Imaging, Digital Recording, and New Types of Solid-State X-Ray Imaging Devices

C. Changes and Additions to Definitions and Applicability Statements

D. Information to be Provided to Users (§ 1020.30(h))

E. Increase in Minimum Half-Value Layer (§ 1020.30(m)(1))

F. Change in the Requirement for Fluoroscopic X-Ray Field Limitation and Alignment (§ 1020.32(b))

G. Revisions and Change in the Limits to Maximum Air Kerma Rate (§ 1020.32(d) and (e))

H. New Modes of Image Recording

I. Entrance Air Kerma Rate at the Fluoroscopic Image Receptor

J. Requirement for Minimum Source-Skin Distance for Small C-Arm Fluoroscopic Systems (§ 1020.30(g))

K. Requirements for Display of Fluoroscopic Irradiation Time, Air Kerma Rate, and Cumulative Air Kerma (§ 1020.32(h) and proposed (k))

L. “Last-Image Hold” Feature on Fluoroscopic Systems (Proposed § 1020.32(j))

M. Modification of Previously Manufactured and Certified Equipment

N. Modification of Warning Label (§ 1020.30(j))

O. Corrections of § 1020.31(f)(3) and (m)

P. Corrections to Reflect Changes in Organizational Name, Address, and Law (§ 1020.30(c), (d), and (q))

Q. Removal of Reference to Special Attachments for Mammography

R. Change to the Applicability Statement for § 1020.32

S. Republication of §§ 1020.30, 1020.31, and 1020.32

III. Proposed Effective Date

IV. Environmental Impact

V. Paperwork Reduction Act of 1995

VI. Analysis of Impacts

A. Introduction

B. Objective of the Proposed Rule

C. Risk Assessment

D. Constraints on the Impact Analysis

E. Baseline Conditions

F. The Proposed Amendments

G. Benefits of the Proposed Amendments

H. Estimation of Benefits

I. Costs of Implementing the Proposed Regulations

J. Small Business Impacts

K. Reporting Requirements and Duplicate Rules

L. Conclusion of the Analysis of Impacts

VII. Federalism

VIII. Submission of Comments

IX. References

I. Background

The SMDA (Public Law 101-629) transferred the provisions of the Radiation Control for Health and Safety Act of 1968 (RCHSA) (Public Law 90-602) from title III of the Public Health Service Act (PHS Act) (42 U.S.C. 201
et seq
.) to chapter V of the act (21 U.S.C. 301
et seq
.). Under the act, FDA administers an electronic product radiation control program to protect the public health and safety. FDA also develops and administers radiation safety performance standards for electronic products.

The purpose of the performance standard and these proposed amendments is to improve the public health by reducing exposure to and the detriment associated with unnecessary ionizing radiation from diagnostic x-ray systems while assuring the clinical utility of the images.

In order for mandatory performance standards to provide the intended public health protection, the standards must be modified when appropriate to reflect changes in technology or product usage. A number of technological developments have been or will soon be implemented for radiographic and fluoroscopic x-ray systems. Such developments, however, are not addressed in the current standard, but have presented problems in the application of the current performance standard.

FDA thus is proposing to amend the performance standard for diagnostic x-ray systems and their major components in §§ 1020.30, 1020.31, 1020.32, and 1020.33(h) (21 CFR 1020.30, 1020.31, 1020.32, and 1020.33(h)).

These proposed amendments will require additional features on newly manufactured x-ray systems that physicians may use to minimize x-ray exposures to patients. Advances in technology have made several of these newly required features possible or feasible at minimal cost.

In the
Federal Register
of August 15, 1972 (37 FR 16461), FDA issued a final rule for the performance standard, which became effective on August 1, 1974. Since then, FDA has made several

amendments to the performance standard to incorporate new technology, to clarify misinterpreted provisions, or to incorporate additional requirements necessary to provide for adequate radiation safety of diagnostic x-ray systems. (See, e.g., amendments published on October 7, 1974 (39 FR 36008); February 25, 1977 (42 FR 10983); September 2, 1977 (42 FR 44230); November 8, 1977 (42 FR 58167); May 22, 1979 (44 FR 29653); August 24, 1979 (44 FR 49667); November 30, 1979 (44 FR 68822); April 25, 1980 (45 FR 27927); August 31, 1984 (49 FR 34698); May 3, 1993 (58 FR 26386); May 19, 1994 (59 FR 26402); and July 2, 1999 (64 FR 35924)).

In the
Federal Register
of December 11, 1997 (62 FR 65235), FDA issued an advance notice of proposed rulemaking requesting comments on the proposed conceptual changes to the performance standard. The agency received 12 comments from State and local radiation control agencies, manufacturers, and a manufacturer organization. FDA considered these comments in developing this proposal. In addition, the concepts embodied in these proposed amendments were discussed on April 8, 1997, during a public meeting of the Technical Electronic Product Radiation Safety Standards Committee (TEPRSSC). TEPRSSC is a statutory advisory committee (21 U.S.C. 360kk(f)(1)(A)) that FDA is required to consult before it may prescribe any electronic product performance standard under the act. The proposed amendments themselves were discussed in detail with the TEPRSSC during its meeting on September 23 and 24, 1998. TEPRSSC approved the content of the proposed amendments and concurred with their publication for public comment.

The proposed amendments described in section II of this document may be considered as nine significant amendments to the current standard and several other minor supporting changes, corrections, or clarifications. The nine principal amendments fall into the following three categories:

1. Amendments requiring changes to equipment design and performance;

2. Amendments designed to improve use of fluoroscopic systems by requiring enhanced information to users; and

3. Amendments applying the standard to new features and technologies associated with fluoroscopic systems.

II. Proposed Amendments to the Performance Standard for Diagnostic X-Ray Systems and Their Major Components

A. Change in the Quantity Used to Describe X-Radiation From Exposure to Air Kerma

FDA proposes to change the quantity and the associated unit used to describe the radiation emitted by the x-ray tube or absorbed in air. The radiation quantity “exposure” would be replaced by the quantity “air kerma.” The units used to describe these quantities would be changed accordingly throughout the standard, wherever appropriate.

The International System of Units (SI) was named and adopted at the 11th General Conference on Weights and Measures (GCWM) in 1960 as an extension of the earlier metric systems. The SI, also referred to as the metric system, is the approved system of units for use in the United States. The U.S. Department of Commerce published an “Interpretation and Modification of the International System of Units for the United States” in the
Federal Register
on December 10, 1976, which set forth the interpretation of the SI system for the United States. The Omnibus Trade and Competitiveness Act of 1998 amended the Metric Conversion Act of 1975 to require each Federal agency to use the metric SI system in its activities. The FDA policy for use of metric measurements is described in a March 19, 1990, memorandum. This policy calls for use of the metric units followed by a parenthetic “inch-pound” declaration unless there is a cogent reason not to utilize dual metric and “inch-pound” measurements. The policy notes that there should be few such exceptions.

One of the objectives of the International Commission on Radiation Units and Measurements (ICRU) is to develop internationally accepted recommendations regarding quantities and units of radiation and radioactivity. The ICRU recommendations often form the basis of GCWM actions. In 1998, the ICRU published its Report 60, “Fundamental Quantities and Units for Ionizing Radiation,” superseding its previous Report 33. Report 60 uses the SI units and special names for some radiation units (Ref. 1). The ICRU had suggested phasing out by 1985 the use of certain special quantities and units that were not part of the SI system, including the special unit of exposure, the roentgen (R).

The current Federal performance standard for diagnostic x-ray equipment uses the special quantity exposure to describe the radiation emitted from an x-ray system. In the
Federal Register
of May 3, 1993 (59 FR 26386), FDA published a final rule which made a partial transition to the SI units by changing the unit for exposure from “roentgen” (R) to “coulomb per kilogram” (C/kg). This change required using an awkward conversion factor of 2.58 x 10
-4
C/kg per R.

In view of current trends, scientific practice, the U.S. policy, and FDA directives, FDA proposes that a complete conversion be made to the SI quantities and units by amending the standard to require using the quantity air kerma in place of the quantity exposure. Additionally, the agency proposes that, in making this conversion, the absolute magnitude of the limits on radiation contained in the standard not be changed. This requires that the limits, when expressed in the new quantity air kerma and its unit, the gray, be expressed with numerical values different from the current limits that use the quantity exposure.

In its recent reports, the National Council on Radiation Protection and Measurement (NCRP) adopted the use of the SI quantity kerma, in particular air kerma, to describe the radiation emitted from an x-ray system. This change in the NCRP recommendations was made without significant concern that previous limits in the voluntary recommendations were slightly increased by this change when numerical values for the limits were not changed but were expressed in the new units. This change in the NCRP recommendations resulted in an increase in the limits, compared to previous recommendations, of about 15 percent.

FDA is not proposing such an increase in this proposal. Instead, FDA is proposing that the numerical values for limits in the standard relating to radiation, when expressed in the new quantity, be changed as well so the new limits will be equivalent to the current limits, thereby making no change to the level of radiation protection provided by the standard. FDA has dropped earlier draft proposals to change the numerical values in a manner similar to the changes made to the voluntary recommendations by the NCRP because of several comments that were received. The comments objected to any changes to the level of radiation protection provided by the limits in the current mandatory standard.

This proposed approach to the numerical limits results in numerical values that are not integer numbers or multiples of 5 or 10, as is the case in the current standard, when limits are expressed in the non-SI unit for

exposure, roentgen. For example, the current limit for an exposure rate of 10 R/minute (R/min), 2.58 x 10
-3
C/kg per min, becomes an air kerma rate (AKR) limit of 88 milligray per minute (mGy/min) under the proposed approach.

FDA is proposing new definitions of the quantities kerma, as used by the ICRU, and air kerma in § 1020.30(b). Because the quantity air kerma is a different quantity from exposure and not numerically equivalent, FDA is proposing in the amended standard to express the limits in terms of air kerma and indicate the equivalent limit in terms of exposure using the word “vice” to indicate this equivalence. Thus, the change described above would be given in the proposed amendments as a limit expressed as “88 mGy/min (vice 10 R/min)” indicating that the new limit of 88 mGy/min air kerma is equivalent to the previous limit 10 R/min exposure.

Current International Electrotechnical Commission (IEC) standards for diagnostic x-ray systems use the quantity air kerma to describe the radiation emitted by the x-ray system. The current limits on maximum fluoroscopic exposure rates in the performance standard were established to be consistent with the recommendation of the NCRP. The proposed amendment maintains agreement between the performance standard and the voluntary standards in terms of the quantities and units used. But in order to maintain the current level of radiation protection and in response to the comments received, the change results in numerical limits for some of the requirements different from those used in the current recommendations of the NCRP.

The term “exposure” is also used with a second meaning in the performance standard that does not refer to a quantity of radiation as defined here. The second meaning of “exposure” refers to the process or condition during which the x-ray tube is activated by a flow of current to the anode and radiation is produced. The second meaning of exposure will continue to be used where appropriate. FDA is proposing to revise the definition of the quantity exposure in § 1020.30(b) to match the current ICRU definition.

FDA also proposes in § 1020.30(b) to amend the definitions of “half-value layer” (HVL) and “x-ray field” to reflect the change from the quantity exposure to air kerma.

B. Clarification of Applicability of Requirements to Account for Technological Developments in Fluoroscopic X-Ray Systems Such as Digital Imaging, Digital Recording, and New Types of Solid-State X-Ray Imaging Devices

When the performance standard was originally developed, the only means for producing a fluoroscopic image was either a screen of fluorescent material or an x-ray image intensifier tube. Thus, the standard was originally written with these two types of image receptors in mind. The advent of new types of image receptors, such as solid-state x-ray imaging (SSXI) devices, and new modes of image recording, such as digital recording to computer memory or other media, has made the application of the current standard to systems incorporating these new technologies cumbersome and awkward. These new aspects of fluoroscopic system design have required a series of interpretations to apply the standard appropriately. With this in mind, FDA proposes to amend the performance standard to recognize these new types of image receptors and modes of image recording and to clarify how the requirements of the standard apply in each case. This amendment would result in replacing the terms “x-ray image intensifier” or “image intensifier” with the more general term “fluoroscopic image receptor” in numerous sections.

Although the basic radiation protection and safety requirements for fluoroscopic equipment in the performance standard are based on the presence of an x-ray image intensifier, these requirements are also appropriate for newer imaging systems that do not use an x-ray image intensifier. The newer imaging systems may incorporate an image receptor consisting of an absorbing material and an array of solid state transducers that intercepts x-ray photons and directly converts the photon energy into a modulated electrical signal. The signal often goes through analog-to-digital conversion as part of the image formation process to perform both fluoroscopy and radiography. FDA proposes to modify the structure and organization of the standard to address this new type of x-ray imaging equipment. The specific changes proposed are described below in section II.C of this document.

For SSXI, new performance considerations are relevant because of the different construction and the use of solid-state materials such as silicon and selenium. These new considerations include: Changes in spatial resolution, as quantified in the modulation transfer function (MTF), dynamic range, and detective quantum efficiency; the introduction of aliasing artifacts; reduced geometrical efficiency (fill factor); and differences in the range of quantum-limited operation when compared to the older vacuum-tube-based fluoroscopic equipment. Because consensus is not available on some aspects of the performance for these new devices, the agency has relied on premarket review and associated guidance documents to provide the necessary radiation safety control for these devices. (See, e.g., the “Guidance for the Submission of 510(k)s for Solid State X-Ray Imaging Devices ” (Ref. 2).)

An example of a new performance consideration for the SSXI is the active detector area. Because of the need for electrical separation/insulation between individual detector elements, the detector area has both active and inactive regions, in terms of detecting image information. The relative areas of the active and inactive detector areas are usually described in terms of the fill factor. The fill factor, to a first approximation, is the pixel area (active area in terms of image formation) times the number of pixels divided by the total detector area exposed to the input image flux.

The fill factor and other characteristics can have significant effects on imaging performance. The imaging performance must also be considered when obtaining a complete picture of the effectiveness of these devices. Although FDA is not offering specific proposals for imaging performance at this time, FDA is inviting comment on possible approaches to ensuring radiation protection and safety in the application of these SSXI devices.

C. Changes and Additions to Definitions and Applicability Statements

To address the changes in technology and the new types of image receptors and to allow these items to be appropriately integrated into the standard, FDA proposes the following changes in definitions and applicability sections of the standard. The changes in definitions described here are in addition to those described above in section II.A of this document.

First, in § 1020.30(b), FDA proposes to amend the definition of “fluoroscopic imaging assembly,” “image receptor,” “spot-film device,” and “x-ray table” by removing the reference to an x-ray image intensifier as the descriptor of the image receptor or by replacing image intensifier with the more general term fluoroscopic image receptor.

Second, FDA also proposes in § 1020.30(b) to amend the definition of the term “recording” by removing the word “permanent” and replacing it with the word “retrievable,” and to remove the examples of “recording,” to clarify the definition of the term “recording” in the context of images stored on recording media other than film.

Third, in § 1020.30(b), FDA proposes to clarify the applicability of the standard or to bring precision to the meaning of specific requirements by adding definitions for the terms solid state x-ray imaging device, fluoroscopy, radiography, non-image intensified fluoroscopy, automatic exposure rate control, isocenter, last image hold (LIH) radiograph, mode of operation, and source-skin distance (SSD).

Last, under § 1020.30(b), FDA proposes to add a definition of “lateral fluoroscope” to clarify the distinction between a lateral fluoroscope and what is commonly referred to as a C-arm fluoroscope. In an August 29, 1977, Compliance Policy Guide, FDA described the geometry for measuring, during a compliance test, the entrance exposure rate for lateral fluoroscopes. The standard does not define a system by the way it is used but allows the manufacturer to specify the use for which the equipment is designed. The design of the system determines whether the system is a C-arm or a lateral fluoroscope. If the system is a C-arm, it is tested using the test geometry for a C-arm system, even if it is used with a lateral beam direction. If the system is a dedicated lateral fluoroscope used with a biplane system, the more restrictive measurement geometry, as described for a lateral fluoroscope in the current § 1020.32(d)(4)(iv) and (e)(3)(iv), will be used. This test geometry is described in proposed § 1020.32(d)(3)(v).

The lateral fluoroscope consists of a support structure holding a tube housing assembly and a fluoroscopic imaging assembly with the x-ray beam in a lateral projection parallel to the plane of the tabletop. Thus, the geometry of the source and image receptor is fixed relative to the patient or x-ray table. The entrance air kerma would be measured with the radiation measurement instrument detector placed 15 centimeters (cm) from the center of the table in the direction toward the x-ray source. (This position is considered to be typical of the entrance skin surface of the patient.) During the measurement, the tube housing assembly is positioned as close to this location as allowed by the system. For C-arm system measurement geometry, the patient is assumed to be as close to the image receptor as possible and, therefore, the detector is placed 30 cm from the entrance surface of the image receptor. In a lateral fluoroscope, the patient cannot be placed against the image receptor, and the measurement point is referenced to the center of the table. The standard does not require that the table have the centerline indicated. Testing is performed relative to the centerline and the center is located by measurement if necessary.

Additionally, FDA proposes to correct two minor typographical errors that were introduced into the definitions of “leakage technique factors” and “spot-film device” in the May 3, 1993,
Federal Register
.

FDA proposes in §§ 1020.31 and 1020.32 to amend the applicability statements by removing the reference to an x-ray image intensifier as the descriptor of the image receptor used to distinguish between radiography and fluoroscopy. FDA proposes to further modify the applicability statements to clearly identify the type of x-ray imaging equipment to which each section applies and to distinguish between radiographic and fluoroscopic imaging.

Additionally, to complete the transition to the use of the terminology “fluoroscopic image receptor,” FDA proposes in § 1020.32(a)(1) and (a)(2), to replace the term “image intensifier” with the more inclusive term “fluoroscopic image receptor” to reflect the changes in fluoroscopic image receptor technology and design. This change will, therefore, include SSXI devices, x-ray image intensifiers, and other fluoroscopic image receptors within the transmission limit and measurement criteria of paragraphs (a)(1) and (a)(2).

Similarly, FDA proposes in § 1020.32(g) to remove “image-intensified fluoroscope” and add in its place the generic term “fluoroscope” in the description of the requirement for minimum SSD for systems intended for specific surgical applications.

Finally, in § 1020.32(i), FDA proposes to remove the term “intensified imaging” and add in its place “image receptor incorporating more than a simple fluorescent screen.” This removes the reference to a specific type of fluoroscopic image receptor, the image intensifier, and includes all types of receptors other than a simple fluorescent screen as meeting the requirement of § 1020.32(i).

D. Information to be Provided to Users (§ 1020.30(h))

FDA proposes to add two paragraphs to § 1020.30(h). Proposed § 1020.30(h)(5) and (h)(6) would require manufacturers to provide in the instructions for users additional information regarding fluoroscopic x-ray systems.

Recent developments in the technology of fluoroscopic systems have resulted in equipment being increasingly provided with a variety of special modes of operation and methods of recording fluoroscopic images. Some of these modes of operation may significantly increase the entrance AKR to the patient compared to conventional fluoroscopy. There is concern that the operating instructions provided with the fluoroscopic system lack sufficient information concerning the characteristics of these special modes of operation to permit the operator to adequately evaluate the increased radiation output and consequent increased exposure to the patient and operator from these modes of operation. There is typically little information provided to users on the clinical procedure(s) for which each mode was designed, resulting in potential inappropriate application of the mode by a user who is not fully aware of the intended application of the particular mode of operation.

Proposed § 1020.30(h)(5) would require that the information provided to users contain a detailed description of each mode of operation and specific instructions on the manner in which the mode is engaged or disengaged. The manufacturer would also be required to provide information on the specific types of clinical procedures or imaging tasks for which the mode is intended and instructions on how each mode should be used. This information is to be provided in a special section of the user’s instruction manual or in a separate manual devoted to this purpose.

Section 1020.30(h)(1)(i) of the performance standard states that the information to users shall contain “Adequate instructions concerning any radiological safety procedures and precautions which may be necessary because of unique features of the equipment * * *.” FDA considers any mode of operation that yields an entrance AKR above 88 mGy/min to be a unique feature of the specific fluoroscopic equipment and thus must have a full and complete description in the instructions for its use.

FDA is also of the opinion that, for modes of operation where the entrance

AKR exceeds 88 mGy/min, the manufacturer should provide detailed information to permit the user to assess the exposure to the patient relative to that delivered in the normal mode of operation. Such information would give operators important radiation safety data with which to make better judgments on the possible hazards involved with a particular procedure. FDA has learned that, because of the multiple number of modes and options available with many of the systems, many users are not aware of when or how such modes are engaged and disengaged or the radiation output consequences of such modes. FDA had originally considered requiring the manufacturer to provide data on the entrance AKRs for each mode of operation of the fluoroscopic system. However, the large number of possible combinations of modes and options for operation available with many of the systems makes this impractical. The proposed amendment described in section II.J of this document would require the manufacturer to provide a display of the AKR and cumulative air kerma. With this information, the user is made aware of the relative changes in the AKR when changing from one mode of operation to another. Awareness of such changes will inform the user of the relative output changes of the system as a function of mode of operation, patient size, and system geometry.

FDA believes that manufacturers are already providing much of the information proposed in this requirement. However, the information may not be displayed in a separate section of the manual where users can readily find it, and the information may not contain enough detailed information on the intended use of the various modes of operation to assure proper use of the system.

Proposed § 1020.30(h)(6) would require manufacturers to provide users with information regarding the new features of fluoroscopic systems described in proposed § 1020.32(k). Proposed § 1020.30(h)(6) would also require manufacturers to provide information regarding the display of values of AKR and cumulative air kerma. This information will include a statement of the maximum deviation of the actual values of AKR and cumulative air kerma from their displayed values, maintenance and instrumentation calibration information, and a description of the spatial coordinates of the reference location for which the displayed values are given.

E. Increase in Minimum Half-Value Layer (§ 1020.30(m)(1))

FDA proposes to modify the requirement for minimum HVL to recognize changes in x-ray tube and x-ray generator technology over the last few decades.

The use of x-ray filtration to increase the quality or homogeneity of an x-ray beam through selective absorption of the low energy photons has been a recommended practice for a long time. A 1968 report published by NCRP (appendix B, table 3, in Ref. 3) provides the beam quality in terms of HVL, as a function of tube potential, that would result from specified values of total x-ray filtration in the x-ray beam. However, the values of HVL in the table would only result if one used the NCRP suggested values of total filtration in diagnostic x-ray equipment of that era (i.e., the 1960s to early 1970s). It should be noted that diagnostic x-ray equipment of that era was characterized by x-ray tubes with a large x-ray target angle and x-ray generators with significant ripple in the high voltage waveform (e.g., an x-ray target angle of 22° and a high voltage ripple of 25 percent).

The requirements on beam quality in the current IEC international standard (Ref. 4) are also expressed in a similar manner as the NCRP Report No. 33 (i.e., a total filtration requirement plus a set of minimum HVL values). The Institute of Physical Sciences in Medicine has recently published a report which can be used to estimate the total filtration from HVL data as a function of x-ray target angle and high voltage ripple (Ref. 5). These data point out the lack of correspondence between a total filtration of 2.5 millimeters (mm) of aluminum and the minimum HVL requirements in the performance standard for state-of-the-art x-ray equipment (e.g., an x-ray target angle of 12° and a high voltage ripple of 10 percent). For these types of equipment, the minimum HVL requirements in the performance standard can be met with about 1.8 mm of total filtration versus the required 2.5 mm of total filtration as specified in the IEC standard (Ref. 4). Only equipment with large x-ray target angles (22°) and a great deal of high voltage ripple (25 percent) need a total filtration of 2.5 mm of aluminum to meet the minimum HVL requirements in the performance standard. In terms of skin-sparing effect, the performance-oriented set of minimum HVL values in the performance standard have not kept up with changes in x-ray equipment when compared to the design-oriented requirement of a total filtration of 2.5 mm of aluminum.

For these reasons, FDA proposes to increase the minimum HVL values for radiographic and fluoroscopic equipment excluding mammography equipment and dental equipment designed for use with intraoral image receptors. The proposed minimum HVL values represent the values obtained with a total filtration of 2.5 mm of aluminum on state-of-the-art diagnostic x-ray equipment (i.e., an x-ray target angle of 12° and a high voltage ripple of 10 percent). FDA used the data in the Institute of Physical Sciences in Medicine report to arrive at the proposed minimum HVL values.

As a separate x-ray filtration issue, there has been a substantial increase over the past 20 years in the use of x-ray fluoroscopy as a visualization tool for a wide range of diagnostic and therapeutic procedures. Because of the long catheter manipulation times and the need, in some cases, for a stationary x-ray field, these procedures have the potential, sometimes realized, for high radiation dose to patients and clinical personnel (Ref. 6). In fact, the agency has been actively involved in promoting recommendations for the avoidance of serious, x-ray-induced, skin injuries to patients during fluoroscopically-guided interventional procedures. As a result, there continues to be an interest in dose reduction techniques for these procedures.

In general, the addition of either beam-hardening or K-edge x-ray filters can provide a significant reduction in the exposure, particularly skin exposure, to the patient. However, this reduction in exposure is accompanied by an attendant increase in tube load (Ref. 7). It should be noted that one of the recommendations of the work group on the technical aspects of fluoroscopy at the 1992 American College of Radiology (ACR)/FDA workshop on fluoroscopy (Ref. 8) was to increase the minimum HVL. Therefore, FDA is also proposing an additional requirement for fluoroscopic x-ray systems incorporating x-ray tubes of high heat-load capacity. Manufacturers of these systems would be required to provide a means, at the user’s option, for adding additional x-ray filtration over and above the amount needed to meet the proposed new minimum HVL values. This requirement is based on the assumption that x-ray tubes with high heat-load capacity are typically required or provided on equipment designed for use in interventional procedures due to the imaging task requirements and the extended exposure times associated with interventional procedures. The

method of implementation and the actual values of additional filtration to realize the reduction in skin exposure will be left to the discretion of the manufacturer.

F. Change in the Requirement for Fluoroscopic X-Ray Field Limitation and Alignment (§ 1020.32(b))

FDA proposes to reorganize and add new paragraphs to § 1020.32(b) to require improved x-ray field limitation for fluoroscopic x-ray systems. Section 1020.32(b) would be reorganized to retain the current requirements applicable to systems manufactured before the effective date of these amendments. For systems manufactured after the effective date, new requirements are proposed in § 1020.32(b)(4) and (b)(5) respectively, for systems with inherently circular or rectangular image receptors. These proposed new requirements will result in increased geometric efficiency or more efficient use of radiation as described below.

The proposed reorganization and retention of the existing requirements in § 1020.32(b) will be accomplished in the following manner: Section 1020.32(b)(1)(i) will be redesignated as § 1020.32(b)(3); § 1020.32(b)(1)(ii) and (b)(2)(iii) will be combined and redesignated as § 1020.32(b)(1) with appropriate revisions to paragraph references to reflect the reorganization of § 1020.32(b); § 1020.32(b)(2)(iv) will be redesignated as § 1020.32(b)(2) with a minor clarification; and § 1020.32(b)(3) will be moved and redesignated as new § 1020.32(b)(6). Additionally, § 1020.32(b)(2)(i) and (b)(2)(ii) will be moved to §1020.32(b)(4)(i) as § 1020.32(b)(4)(i)(A) and (b)(4)(i)(B).

New requirements of improved efficiency for systems manufactured after the effective date of the amendments are proposed in § 1020.32(b)(4)(ii) for systems with inherently circular image receptors. Section 1020.32(b)(5) would contain the field limitation requirements for systems with inherently rectangular image receptors. The requirements proposed for systems with rectangular image receptors are the same as those currently applicable to radiographic systems provided with positive beam limitation or to spot-film devices that utilize rectangular image receptors. As such, the proposed tolerances for x-ray field limitation are considered technically feasible.

A reduction in unnecessary patient exposure is the basis for all of the x-ray field limitation and alignment requirements in the performance standard. For example, any radiation falling outside the visible area of the image receptor provides no useful diagnostic or visualization information and, therefore, represents unnecessary patient exposure. Once it is recognized that restricting the size of the x-ray field provides an effective control of unnecessary radiation exposure, the question shifts to what is the tolerance technically achievable by the manufacturer for the matching of the x-ray field and the visible area of the image receptor.

The current performance standard (§ 1020.32(b)(2)(i)), states “neither the length nor the width of the x-ray field in the plane of the image receptor shall exceed that of the visible area of the image receptor by more than 3 percent of the SID. The sum of the excess length and the excess width shall be no greater than 4 percent of the SID.” These requirements result in worst-case values of geometrical efficiency enumerated in table 1 of this document for what are typical geometrical and operating conditions on fluoroscopic systems. Geometrical efficiency is defined as the ratio of the visible area divided by the area of the x-ray field. It should be noted that the requirements in the existing IEC international standard with respect to x-ray field limitation are more stringent than in the performance standard (Ref. 4). When the x-ray field is rectangular and the visible area is circular, the IEC standard requires that the length and width of the x-ray field be less than the diameter of the maximum visible area of the image intensifier. Thus, if the x-ray field is centered on the visible area of the image intensifier, the x-ray field would exceed the visible area of the image intensifier only in the corners of a rectangular x-ray field, unlike what could result from following the current performance standard.

Table 1.—Worst-Case Geometrical Efficiency in Percentage for a Fluoroscopic System
1

Visible Area (circular, cm
2
)

X-Ray Field (worst case, square, cm
2
)

Efficiency (%)

113
196
57

177
289
61

415
625
66

707
1,024
69

1
Worst-Case Geometrical Efficiency in Percentage for a Fluoroscopic System With a Source-Image Receptor Distance (SID) of 100 cm, a Square X-Ray Field Size at the Limits Allowed by § 1020.32(b)(2)(i), and Image Intensifiers With 12-, 15-, 23-, and 30-cm Diameter Visible Areas.

As can be seen from table 1 above, the current performance standard allows the possibility of relatively low geometrical efficiency, particularly in modes of operation corresponding to small visible areas on the image intensifier. It should be noted that many fluoroscopically-guided interventional procedures involve the use of small visible areas on the image intensifier (Ref. 9). These low values of geometrical efficiency are a direct result of using a square collimator for the x-ray field when faced with an inherently circular visible area for the image receptor. The use of a continuously adjustable, circular collimator and/or circular apertures along with adjustable rectangular collimation would increase the geometrical efficiency.

Many currently marketed x-ray systems suitable for fluoroscopically-guided interventional procedures provide continuously adjustable, circular collimators as a basic and/or optional capability (Ref. 10). Thus, a continuously adjustable, circular collimator is technically feasible, albeit at some additional cost to the user community. Fluoroscopic x-ray systems with this feature can provide a substantial increase in geometrical efficiency that is important for all types of radiological procedures but particularly important for interventional procedures resulting in high skin exposure.

It is for these reasons that FDA proposes to require geometrical efficiencies of 80 percent or more for all fluoroscopic x-ray systems. When the visible area of the image receptor is

greater than 34 cm in any direction, a geometrical efficiency of 80 percent is no longer sufficiently stringent. FDA proposes to change the requirement to a sizing tolerance at that point (i.e., the x-ray field measured along the direction of greatest misalignment with the visible area of the image receptor shall not extend beyond the visible area of the image receptor by more than 2 cm). This oversizing tolerance will ensure geometrical efficiencies of better than 80 percent for large image receptors. In those unusual cases where the x-ray field is not uniformly intense over its cross-section, the proposed field limitation and alignment requirement provides for measurement of efficiency in terms of air kerma integrated over the x-ray field incident on the visible area of the image receptor (Ref. 11).

The intent is to promote the incorporation of continuously adjustable, circular collimators into all types of fluoroscopic x-ray systems with circular image receptors. FDA acknowledges that the new requirements could be met through the use of less complex, currently available, rectangular collimation and underframing. For example, the amount of underframing (defined as the difference in the width of the x-ray field versus the diameter of the visible area) of a rectangular x-ray field needed to meet the new requirements is enumerated in table 2 of this document for the same geometrical and operating conditions of fluoroscopic systems described in table 1 of this document. The agency is soliciting comments on the ramifications of this amount of underframing. These proposed requirements for increased x-ray utilization efficiency would appear in proposed § 1020.32(b)(4)(ii) for systems manufactured after the effective date of the amendments.

Table 2.—Underframing of a Rectangular X-Ray Field
1

Visible Area Diameter (cm)
X-Ray Field Width (cm)
Underframing (cm)

12
11.9
-0.1

15
14.9
-0.1

23
22.8
-0.2

30
29.7
-0.3

1
Amount of Underframing of a Rectangular X-Ray Field Needed to Meet the New Field Limitation Requirements for a Fluoroscopic System With an SID of 100 cm and Image Intensifiers With 12-, 15-, 23-, and 30-cm Diameter Visible Areas.

Although the field limitation requirements for fluoroscopic equipment in the performance standard are predicated on the presence of an x-ray image intensifier, the requirements are also appropriate for newer imaging systems that do not use an x-ray image intensifier. As mentioned previously, the newer imaging systems may incorporate an image receptor consisting of an absorbing material backed by an array of solid state transducers that intercepts x-ray photons and converts the photon energy into a modulated electrical signal with eventual analog-to-digital conversion. These image receptors are inherently rectangular. As is the case for image intensifier based systems, magnification modes are available through the use of a “digital zoom” where only a selected portion of the digital array is visible to the operator. FDA is proposing to apply the current requirements of the standard for x-ray field limitation that are used for spot-film devices or radiographic systems equipped with positive beam limitation, and which also use rectangular fields, to this new type of image receptor. These requirements result in worst-case values of geometrical efficiency (defined as the square visible area divided by the area of a square x-ray field) enumerated in table 3 of this document for what are typical geometrical and operating conditions of fluoroscopic systems.

Table 3.—Worst-Case Geometrical Efficiency in Percentage for a Fluoroscopic System
1

Visible Area Diameter (square, cm
2
)

X-Ray Field (square, cm
2
)

Efficiency (%)

144
196
73

225
289
78

529
625
85

900
1,024
88

1
Worst-Case Geometrical Efficiency in Percentage for a Fluoroscopic System With an SID of 100 cm, a Square X-Ray Field Size at the Limits Allowed by § 1020.32(b)(2)(i), and Solid-State X-Ray Images with 12 cm x 12 cm, 15 cm x 15 cm, 23 cm x 23 cm, and 30 cm x 30 cm Visible Areas.

As can be seen from table 3 above, the current standard provides relatively high geometrical efficiency. In this case, the high values of geometrical efficiency are a direct result of using a rectangular collimator for the x-ray field when faced with an inherently rectangular visible area for the image receptor. Proposed § 1020.32(b)(5) would explicitly state the field limitation requirements for systems with inherently rectangular image receptors.

G. Revisions and Change in the Limits to Maximum Air Kerma Rate (§ 1020.32(d) and (e))

In § 1020.32, FDA proposes to revise and reorganize § 1020.32(d) and (e) to clarify and simplify the requirements on maximum AKR for fluoroscopic x-ray systems. In § 1020.32(d), FDA proposes to incorporate all of the requirements for AKR limits regardless of the date of manufacture of the x-ray system. The revised paragraph would also incorporate the new quantity kerma and the corresponding limits on entrance

AKRs. FDA proposes to move the current requirements of § 1020.32(e) that are applicable to equipment manufactured on or after May 19, 1995, to the revised § 1020.32(d). This would consolidate all of the requirements for limits on the maximum AKR in a single section (i.e., revised § 1020.32(d)). Section 1020.32(e) would be reserved.

The requirements applicable to fluoroscopic systems manufactured before May 19, 1995, currently contained in § 1020.32(d)(1) through (d)(3), would be contained in revised § 1020.32(d)(1). No change in the limit on maximum AKR for previously manufactured fluoroscopic systems is introduced by the reorganization and simplification of current § 1020.32(d). This simplification is obtained by describing the exceptions to the maximum AKR only one time in proposed § 1020.32(d)(1)(v) rather than three times as in current § 1020.32(d)(1) through (d)(3).

Proposed § 1020.32(d)(1) also includes § 1020.32(d)(1)(iv) that makes explicit the fact that systems manufactured before May 19, 1995, may be modified to comply with new requirements contained in proposed § 1020.32(d)(2). The rationale for this addition is described in section II.M of this document.

Proposed § 1020.32(d)(2) would include the requirements applicable to fluoroscopic systems manufactured on or after May 19, 1995. Section 1020.32(d)(2)(i) would contain the language currently in § 1020.32(e)(1) that requires systems with the capability for AKR greater than 44 mGy/min to be provided with automatic exposure rate control.

Section 1020.32(d)(2)(ii) would contain the requirements of current § 1020.32(e)(2) that became effective on May 19, 1995, and establish an upper limit on the AKR during high-level control mode of operation. Section 1020.32(d)(2)(iii) would incorporate the exceptions to the maximum AKR limit given in § 1020.32(d)(2)(ii). Section 1020.32(d)(2)(ii)(A) would contain the exception currently found in § 1020.32(e)(2)(i) that addresses the recording of images using a pulsed mode applicable to equipment manufactured prior to the effective date of these amendments. For equipment manufactured after the effective date of these amendments, § 1020.32(d)(2)(ii)(B) would add an additional new exception described below in section II.H of this document. Finally, the exception currently found in § 1020.32(e)(2)(ii) addressing high-level control mode of operation would be moved to § 1020.32(d)(2)(ii)(C).

The conditions under which compliance is determined are currently found in § 1020.32(d)(4) and (e)(3). These conditions would be moved to § 1020.32(d)(3). Section 1020.32(d)(3)(vi) would be added to specifically address the measurement conditions for systems with SIDs less than 45 cm. For these systems, FDA is proposing that compliance be determined by measurement at the minimum SSD.

The exemption for radiation therapy simulation systems currently found in § 1020.32(d)(5) and (e)(4) would be incorporated into a proposed revision of § 1020.32(d)(4).

H. New Modes of Image Recording

New requirements would be established in a § 1020.32(d)(2)(iii)(B) to further limit the conditions under which the limit on the maximum AKR rate would not apply. In May 1994, the agency amended the requirements in the standard pertaining to the limit on entrance exposure rate (EER) during fluoroscopy. (For convenience in discussing the current standard and proposed changes, reference will be made to the limits on EER rather than to entrance AKR which will be the quantity used in the amended standard.)

These 1994 amendments prescribed an exception to the limit on EER during the recording of images “from an x-ray image intensifier tube using photographic film or a video camera when the x-ray source is operated in a pulsed mode.” (Pulsed mode is defined as operation of the x-ray system such that the x-ray tube current is pulsed by the x-ray control to produce one or more exposure intervals of duration less than one-half second.) These amendments also prescribed a limit on EER of 20 R/min when an optional high-level control was activated during fluoroscopy.

The basic premise of these amendments was to provide for a set of limits on the maximum EER during fluoroscopy, and for an exception during radiographic modes of operation such as cine-radiography. The defining terms for determining whether the equipment was in fluoroscopy versus radiography mode of operation were “recording of images” and “pulsed mode.” In retrospect, these terms were not explicit enough for making a determination of the mode of operation. For example, the current wording would allow adding a recording device such as a video tape recorder to the imaging chain in a pulsed mode of operation. This would, thereby, circumvent the intent of the regulation and allow the limit on maximum EER during fluoroscopy to be exceeded, even though the recorded images are never used in the radiological examination and are used only for archiving purposes, if used at all.

As mentioned in the earlier discussion on new types of image receptors, FDA is proposing new definitions for fluoroscopy and radiography. These definitions are needed to make a clearer distinction between fluoroscopy and radiography, regardless of the type of image receptor being used. A key element in the new definitions is that radiographic images recorded from the fluoroscopic image receptor must be available for viewing after the acquisition of the images and during or after the procedure, whereas fluoroscopic images are viewed in real time, or near-real time during the procedure. Thus, the definitions of the two modes of operation, i.e., radiography and fluoroscopy, are tied to the intended use, and not to an arbitrary interval of time, as under the current “pulsed mode” definition.

In addition to the proposed new definitions, FDA proposes to change the description of the conditions under which exceptions to the limit on maximum AKR are allowed. Section 1020.32(d)(2(iii) would contain two exemptions. The exemption currently in § 1020.32(e)(2)(i) would be moved to § 1020.32(d)(2)(iii)(A) and would apply to fluoroscopic systems manufactured on or after May 19, 1995, but before the effective date of the proposed amendment. A new exception would be added in § 1020.32(d)(2)(iii)(B). This exception would recognize that image receptors other than x-ray image intensifiers tubes are now used in fluoroscopy and would remove the reference to operation in a pulsed mode. Instead, the exception to the limit on maximum AKR would apply to any recording of images from the fluoroscopic image receptor except when the recording of images is accomplished using a video tape recorder or a video disk recorder. This would prevent the simple addition of an analog image-recording device to the fluoroscopic system as a means to overcome the limit on maximum AKR during normal fluoroscopy.

As discussed in the preamble of the proposed 1993 amendments (58 FR 26407, May 3, 1993), the agency is still interested in receiving information on any clinical situations that could require higher AKR than currently permitted. Such situations have been suggested to arise due to the necessity of momentarily viewing the patient or the state of a device in a patient as best as can be done or with the highest image quality obtainable during fluoroscopy

mode of operation. Some anecdotal evidence seems to argue for an increase in the EER above the current 20 R/min limit under high-level control. The 1994 change in the regulations underwent an extensive review and comment period. The consensus of that review, although not unanimous at the time of issuance of the regulations, was that 20 R/min would be sufficiently high for most clinical fluoroscopy situations. The agency was and is still sensitive to the concern that the limits on EER may in some cases compromise the clinical utility of the fluoroscopic equipment.

Because of these concerns regarding the appropriate upper limit AKR, FDA is encouraging further comment on the topic of limits on AKR under normal and high-level fluoroscopy modes. For example, some members of the radiological community have proposed that fluoroscopic equipment allow a momentary viewing of the state of an intervention at an increased but unspecified AKR. This momentary view would have a maximum duration of 10 to 15 seconds. This proposal was accompanied with the comment that if physicians are not allowed to use such a mode, they will continue the practice of using cineradiography bursts at high AKRs to accomplish the clinical task.

I. Entrance Air Kerma Rate at the Fluoroscopic Image Receptor

Comments received by the agency suggest that an alternative approach in place of or in addition to limits on AKR during fluoroscopy would be more useful and effective in limiting unnecessary radiation and assuring optimum system performance. The suggestion is that the limits on AKR to the patient (represented by a measurement made according to the compliance geometry described in current § 1020.32(e)(3)) be replaced by limits on the entrance AKR at the input surface of the image receptor (EAKIR). Different EAKIR limits could be established for different modes of fluoroscopic imaging, depending on the image performance required for the clinical task.

There is a precedent for this approach in other consensus documents such as the NCRP Report No. 99 and NCRP Report No. 102 (Refs. 12 and 13). For example, the NCRP Report No. 99 states that during fluoroscopy “typical image intensifier entrance exposure should be in the range of 13 to 52 nC/kg/image (50 to 200 μR/image) depending on image intensifier size * * *.” (Note that, in the opinion of FDA, there is an error in the NCRP Report No. 99: these numbers reflect exposure per second, not exposure per image.) In the same manner, the NCRP Report No. 102 provides a table with “air kerma rate values to produce acceptable fluoroscopy images” and “air kerma to produce static images equivalent to that produced by a par speed screen-film system.” FDA invites comments on the feasibility and desirability of this approach to limit unnecessary radiation from fluoroscopic systems.

J. Requirement for Minimum Source-Skin Distance for Small C-Arm Fluoroscopic Systems (§ 1020.32(g))

FDA proposes in § 1020.32(g) to add § 1020.32(g)(2) to establish a minimum source-skin distance (MSSD) for “C-arm” type x-ray systems having source-to-image-receptor distances of 45 cm or less and intended for imaging extremities. This amendment would incorporate into the performance standard the content of variances from the performance standard granted according to § 1010.4.

FDA has granted variances from the requirement set out in §1020.32(g) for a limit on the MSSD for fluoroscopic x-ray systems that were designed as small portable C-arm systems. These are fluoroscopic systems that were originally designed to be hand-held and were used at sporting events for a quick examination/diagnosis of orthopedic injuries. In fact, some of the early systems used a radioisotope instead of an x-ray tube as the source of the radiation and were, therefore, outside the purview of FDA under the RCHSA (although they are regulated as medical devices). Over time, manufacturers of these devices enlarged the distance or opening between the x-ray source and the image receptor to allow examination of larger extremities. The argument was that some athletes had larger extremities and a larger opening was needed to permit the use of the systems on them. The systems were marketed under a variance from § 1020.32(g) and were labeled for extremity use only. As the size of the opening on systems for which variances have been requested has increased from about 20 cm to 35 cm, and manufacturers have increased the radiation output of these systems, the agency has become concerned about the loss of the skin-dose sparing properties of the MSSD requirement. In addition, because a variance is granted for a finite time period, renewal of the variances and the reviewing of new conditions for use present resource implications for FDA and the manufacturers.

The justification for a variance from § 1020.32(g) used by many manufacturers of these small C-arm systems is geometrical scaling. Manufacturers have stated in their variance applications that the MSSD is proportional to the source-image receptor distance in comparison to full-sized C-arm systems. Although extremities can be considered to scale geometrically in a similar manner compared to the trunk or large body parts, other body parts do not scale in such a manner as to maintain a similar skin dose. For the source-image receptor distances used in these systems, evaluation of this geometrical relationship shows that the factor, by which the entrance AKR to the body part increases over that for thinner parts, increases significantly as the thickness of the body part being imaged reaches over 15 or 16 cm. This increase reaches a factor of two for a thickness of 26 cm and increases rapidly for thicker parts. In their original configuration, these devices had a very small opening and could not accommodate anything other than a limb. The latest configurations can easily accommodate the whole body of a neonate or a pediatric patient.

At some point, these systems no longer represent small C-arms for extremity use alone but are simply slightly smaller versions of conventional C-arms for whole-body, general-purpose examinations. If the system can be used for whole-body examination purposes, it should meet the minimum radiation safety standards applicable to conventional C-arm systems. Through the variance petition process, FDA has limited the small C-arm systems to extremity use only.

To incorporate the protection provided by the conditions imposed by the variances and to incorporate this requirement in the performance standard, FDA proposes to limit the source-skin distance to not less than 19 cm for fluoroscopic systems having source-image receptor distances of 45 cm or less. Provision would be allowed for systems designed for specific surgical applications to be operated with a source-skin distance of not less than 10 cm. Systems subject to this requirement would be required to be labeled for use for imaging extremities only. Manufacturers would be required to include appropriate precautions in the information provided to users under § 1020.30(h).

K. Requirements for Display of Fluoroscopic Irradiation Time, Air Kerma Rate, and Cumulative Air Kerma (§ 1020.32(h) and Proposed (k))

FDA is proposing that newly manufactured fluoroscopic systems display directly to the fluoroscopist information related to three

fundamental aspects of patient irradiation—the duration, rate, and amount of x-ray emissions. Generally, fluoroscopic systems do not currently provide such information at all. Irradiation time, AKR, and cumulative air kerma are basic radiological variables important for medical radiation protection. Their values may be applied to the process of optimization (i.e., obtaining radiological images with the least amount of radiation required), to the assessment of radiation detriment as a factor affecting patient-outcome efficacy, and to the development of reference levels representative of normal clinical practice. Optimization, efficacy, and reference levels currently comprise a conceptual vanguard of radiation protection in medicine at the international level (Refs. 14 to 17). When monitored in the clinic, irradiation time, AKR, and cumulative air kerma may be used to indicate risk of acute skin injury arising from potentially prolonged irradiation associated with some interventional procedures (Refs. 18 to 20). Values displayed directly to practitioners as an examination or procedure progresses can feed back to them indices of radiation burden, and practitioners can respond promptly by adjusting protocols and techniques to minimize dose to patients and practitioners as practitioners optimize radiation levels necessary for medical imaging. Moreover, for fluoroscopy and radiography in general, knowledge of irradiation levels at patient skin entrance is an essential starting place for evaluation of absorbed dose to internal tissues (Refs. 9 and 21). Such doses are stochastically linked to cancer morbidity, mortality, and to genetically transmissible defects (Refs. 14 and 22). Estimates of cumulative doses absorbed in tissues foster risk communication between medical staff and patients and, when tracked over time, are effective indicators of practice consistency, variability, or anomaly in the quality assurance activities associated with assuring the safety of clinical procedures.

The need for displays of irradiation variables was recognized at the 1992 national workshop on safety issues in fluoroscopy organized by the ACR and FDA (Ref. 8). In October 1995, the need was also recognized internationally by the workshop on efficacy and radiation safety in interventional radiology, sponsored jointly by the World Health Organization and the Institute of Radiation Hygiene, Radiation Protection Ministry, Federal Republic of Germany (Ref. 23). Recently, requirements for displays of irradiation parameters have been incorporated into an international standard for x-ray systems for interventional radiology (Ref. 24). With the advent of commercially available and relatively inexpensive means to measure and display real-time AKR and cumulative air kerma produced by fluoroscopic systems (Ref. 25), it is feasible as well as desirable to require that this information be directly observable by fluoroscopists at their working positions.

The proposed display requirements would apply to all types of newly manufactured fluoroscopic equipment (i.e., from systems found in cardiac catheterization suites, to equipment used for upper gastrointestinal fluoroscopy, to “mini” C-arms, and also to each fluoroscopic x-ray tube as part of any system). FDA invites comments about whether these requirements would be suitable to all types, or to a limited set of fluoroscopic equipment, namely, to stationary C-arm fluoroscopes that are typically used in interventional procedures.

1. Fluoroscopic Irradiation Time, Display, and Signal

Fluoroscopic irradiation time is profoundly tied to patient dose in a complex way that involves many other factors (e.g., see Ref. 26). FDA believes it advantageous to require that cumulative irradiation-time values be treated in their own right, in addition to the other variables cited in the proposed § 1020.32(k), as radiological parameters whose control would facilitate radiation-protection optimization. Physician members of TEPRSSC pointed out at its September 1998 meeting that irradiation time is the single fundamental variable over which a physician using fluoroscopy has the most direct and easiest control through activating or deactivating x-ray production, typically by means of a pedal switch (Ref. 27).

FDA proposes to add § 1020.32(h)(2) to the regulations to change the current fluoroscopic timer requirement in two ways. First, § 1020.32(h)(2)(i) would require that the values of the cumulative irradiation times associated with each of the fluoroscopic tubes of a system used in an examination or procedure be displayed to the fluoroscopist at his or her working position. The displayed values would be indicated from the beginning, throughout, and after an examination ends, available until the cumulative irradiation timer is reset to zero prior to a new examination. Second, § 1020.32(h)(2)(ii) would require an audible signal cycle different from that of current equipment for each x-ray tube used during an examination or procedure. Contrary to the current provision that allows the timing device to be preset to any interval up until a maximum cumulative irradiation time of 5 minutes, FDA proposes that a signal audible to the fluoroscopist sound at each fixed interval of 5 minutes of irradiation time. Also contrary to the current requirement, instead of sounding until reset, the audible signal would sound (while x-rays are produced) for a minimum of only 1 second, after which the signal could stop until a subsequent 5 minutes of irradiation elapses. The audible signal would not affect the production of x-rays, the display of cumulative irradiation-time values required by § 1020.32(h)(2)(i), or any of the other displays proposed in § 1020.32(k).

Considering advice offered at the 1998 TEPRSSC meeting (Ref. 27), FDA now believes that a fixed, standard (5 minute) period for an alert signal would avoid potential confusion that could ensue with a fluoroscopic timer that is variably preset. For example, such confusion could arise in a busy clinical facility with many different users, where fluoroscopists might not be aware of the need to readjust alert intervals that had been changed previously by other fluoroscopists to accommodate the individual protocol requirements associated with particular patient examinations. Furthermore, FDA believes that an audible signal of short duration would be a more effective and useful alert than a signal that sounds continuously, requires a reset, and therefore, could pose a distraction to users. FDA seeks comments about the audible signal cycle in proposed § 1020.32(h)(2)(ii), particularly in comparison to the suggested alternative below that is not currently in the proposal.

As an alternative approach, the selection of the time period until the alarm sounds could be at the discretion of the fluoroscopist. The timer could be preset to any period (less than, equal to, or greater than 5 minutes), or preset even to not sound at all. Under this approach, before an examination or procedure, the fluoroscopist could select a period beyond which an audible signal would sound until the timer could be reset (or else sound briefly then remain silent until the preset fluoroscopic period elapses again). Presuming clinicians maintain personal cognizance of fluoroscopic timer options and adaptability, such alternatives would offer them flexibility and opportunity to apply standard features of equipment operation to their

own individual clinical protocols and practices.

FDA also seeks comment on whether the display of the cumulative irradiation time should be visible to the fluoroscopist at his or her working position or whether it is sufficient to display the cumulative time at the control console. It has been suggested that this display should be available to the fluoroscopist to permit constant monitoring by the fluoroscopist. Other opinions are that such a display at the working position would only add confusion to an already complex visual environment, and display of the cumulative irradiation time at the x-ray control would make the information available in any case. Display at the fluoroscopist’s working position may be slightly more complex or costly than display at the x-ray control.

2. Displays of Air Kerma Rate and Cumulative Air Kerma

FDA believes that a requirement for displays of AKR and cumulative air kerma values would significantly advance the optimization of radiation safety, in consideration of recent developments in clinical practice and technology (Refs. 23, 25, and 26), an evolving consensus for a radiation-protection framework (Refs. 14 to 17), and specific guidance (Refs. 18 to 20). Air kerma and AKR are fundamental radiological quantities of the amount and rate of charged-particle kinetic energy liberated per mass of air traversed by incident x-rays (Ref. 1). For this reason, FDA proposes to add § 1020.32(k) to require that all new fluoroscopic systems be capable of displaying real-time values of the AKR and cumulative air kerma delivered by each x-ray tube at reference locations representative of x-ray beam entry to the patient skin surface. These displays would be directly discernible at the fluoroscopist’s working position, and the displayed values would deviate by no more than ±25 percent from actual values. To elucidate these requirements and those of the other proposed amendments, the definitions of the terms “fluoroscopy,” “mode of operation,” “and radiography” are proposed in § 1020.30(b). The utility of the display requirements could be broadly leveraged among practitioners in a variety of clinical settings through familiarization with relatively standardized display formats. Such standardization is proposed in § 1020.32(k)(1) through (k)(7), where the particular requirements proposed conform generally to those of the recently published IEC standard (Ref. 24).

During fluoroscopy or while recording images during a fluoroscopic procedure, the displayed value of the AKR would represent in real time the magnitude of air kerma per unit time being delivered at any geometrical point within a specified reference locus. The displayed value of the cumulative air kerma would represent a sum of two parts: (1) The fluoroscopic AKR integrated over an interval until update, and (2) all contributions to the air kerma (at any point in the same reference locus) from radiography occurring in that interval. The cumulative air kerma would be updated throughout the examination or procedure, and the integration interval would be the time between the start of an examination or procedure and the end of the most recent episode of either fluoroscopy or radiography during that same examination or procedure.

For each x-ray tube used during fluoroscopy or during recording of fluoroscopy, the value of the AKR will be displayed. After the cessation of fluoroscopy, the cumulative air kerma will be displayed and will remain displayed until the resumption of fluoroscopy or a radiographic mode is activated or the display is reset for a new patient or procedure. Thus, the cumulative air kerma will be displayed after x-ray production ceases from either fluoroscopy or radiography.

Values of the AKR are displayed at times other than those for the cumulative air kerma in order to underscore the distinction between these two variables and also to reduce the potential for overwhelming the fluoroscopist with too much information presented at once. At any particular moment during an examination or procedure, only values of the irradiation time and AKR (or cumulative air kerma) would be on display for each tube used. If, for example, a biplane fluoroscopic system were used in some cardiac catheterization procedure, two separate sets of values—one set for each of the x-ray tubes of the biplane—would be displayed. Under such circumstances of multiple presentations of related information, it is important that the values displayed be distinguishable enough from each other to be easily recognized and associated with the different radiological variables they represent. For this reason, FDA proposes in § 1020.32(h)(2)(i) and (k)(3) to require that the units of measurement be displayed as well as the values per se. FDA also proposes in § 1020.32(k)(1) and (k)(2) to require that the measurement units mGy/min and mGy be displayed respectively alongside the values for AKR and cumulative air kerma. These values would serve as a labeling distinction to preclude potential confusion of the quantities.

As measures of fundamental radiological quantities, the displayed values of AKR and cumulative air kerma would refer to free-in-air irradiation conditions (i.e., their evaluations would be made minus any contributions of scatter radiation, particularly contributions backscattered from a patient (or from a measurement phantom)). Also, the displayed values would refer to irradiation conditions at a reference location (i.e., at any geometrical point contained within a specific reference locus defined according to the type of fluoroscopic system). Each reference location is intended to represent, at least nominally, a place of x-ray beam entry to the patient skin. For fluoroscopes with the x-ray source below or above the table, or of the lateral type, § 1020.32(k)(5)(i) would have skin-entrance reference locations correspond identically and respectively to those specified in § 1020.32(d)(3)(i), (d)(3)(ii), or (d)(3)(v). These locations define the geometry for measuring compliance with the regulatory maxima of the AKR.

For C-arm type fluoroscopes, however, in many cases the locations proposed for measuring compliance with the regulatory maxima of the AKR, given in § 1020.32(d)(3)(iii) and (d)(3)(iv), would not suitably represent where the x-ray field enters the patient skin. This is especially true for oblique angulations and extended distances between the x-ray source and image receptor. Therefore, in § 1020.32(k)(5)(ii), for C-arm systems, FDA is proposing a skin-entrance reference location for display quantities that is different from the location for measuring compliance with regulatory AKR limits. For evaluation of displayed values, the skin-entrance reference location would be either 15 cm from the isocenter toward the x-ray source along the beam axis (irrespective of angulation) or, alternatively, along the beam axis at a point deemed by the manufacturer to represent the intersection of the x-ray beam and the entrance surface of the patient skin. A definition of “isocenter” is proposed in § 1020.30(b). Proposed § 1020.32(k)(5)(ii) would allow manufacturers to choose either the 15-cm locus or specify the alternative. The alternative locus would offer manufacturers flexibility to provide systems that could evaluate AKR and cumulative air kerma in closer proximity to actual places of x-ray beam entry to patients than could systems with reference skin entrance defined

generically at a 15-cm locus from the isocenter. An alternative skin-entrance reference location may be particularly appropriate for mini C-arm fluoroscopes (i.e., those with SID less than 45 cm, for which the 15-cm locus from the isocenter may be physically unrealizable). In any case, new paragraphs § 1020.30(h)(6)(iii) and (h)(6)(iv) would require that manufacturers identify to the user the spatial coordinates of the irradiation location to which displayed values refer and also provide a rationale justifying any reference location identified as an alternative to the 15-cm locus.

In patient examinations or procedures with C-arm systems, one possible result of having reference locations of x-ray beam skin-entry different from the measurement sites for AKR compliance is that displayed values could actually exceed the regulatory maxima even though the system is fully compliant. Such a situation could arise for some irradiation geometry when the reference skin-entrance location is closer to the x-ray source than is the site for measuring compliance. Displayed values of the AKR and cumulative air kerma are intended to inform the fluoroscopist of radiation burden to the patient. Conversely, the AKR regulatory maxima, practicably measured 30 cm from the imaging-assembly input, according to § 1020.32(d)(3)(iii) or at the minimum SSD according to § 1020.32(d)(3)(iv), are intended to impose upper limits on radiation output that are compatible with the levels needed by the imaging chain for adequate fluoroscopic visualization.

Reset of the displays to zero would occur between sessions with successive patients. Before reset, a final value of the cumulative air kerma may serve to reinforce an association between the culmination of a radiological examination or procedure and the radiation burden incurred by the patient. FDA believes that the availability of this value would greatly facilitate the implementation of previously published recommendations (Refs. 18 to 20) on recording information in the patient’s medical record to identify the potential for serious x-ray-induced skin injuries in order to avoid them.

L. “Last-Image Hold” Feature on Fluoroscopic Systems (Proposed § 1020.32(j))

FDA proposes to add a paragraph to require that all fluoroscopic x-ray systems be provided with a means to continuously display the last image acquired prior to termination of exposure.

The wide availability of electronic methods for the recording and displaying of video images makes possible the provision of a “last-image hold” or “freeze-frame” capability on fluoroscopic x-ray systems. This feature allows the fluoroscopic x-ray system to continuously present a static image of the last fluoroscopic scene captured or presented at termination of the fluoroscopic exposure. This feature also provides the user with the ability to conveniently view fluoroscopic images without continuously irradiating the patient.

This feature is especially useful in procedures such as fluoroscopically-guided needle placement for biopsy or drainage, catheter or tube placement, and other diagnostic or therapeutic interventional procedures. Systems provided with this feature reduce fluoroscopic exposure times while enabling extended examination and planning during fluoroscopically-guided procedures.

This capability is provided as a basic or optional feature on many currently marketed fluoroscopic systems. Many individuals have expressed the opinion that because of the radiation dose reduction afforded by such a feature, it should be provided on all new fluoroscopic systems. Such a recommendation was strongly endorsed at the workshop on fluoroscopy in 1992 (Ref. 8). In addition, a requirement for this capability is included in the recently published IEC standard for the safety of x-ray equipment for interventional radiology (Ref. 24). Establishing this requirement would assure that all new fluoroscopic systems have this patient radiation dose reduction feature and that it is available when its use is appropriate. Without such a requirement, some systems may for economic reasons continue to be purchased without this feature, thereby denying dose reduction benefits to patients.

Proposed § 1020.32(j) would permit the displayed image to be obtained from the last or a combination of the last few fluoroscopic video frames obtained just prior to termination of fluoroscopic exposure or by an alternative implementation via a radiographic exposure automatically produced at termination of the fluoroscopic exposure. Comments are solicited as to whether these approaches to implementation of last image-hold are appropriate and needed.

M. Modification of Previously Manufactured and Certified Equipment

FDA proposes to add language to § 1020.32(d)(1)(iv) and (h) to make explicit the opportunity under § 1020.30(q) for modifications to be made to existing certified x-ray systems. Modifications are currently permitted as long as the modification does not result in a failure to comply with the requirements of the performance standard. Changes in performance resulting from amendments to the performance standard often result in enhanced radiation safety or features not available on previously manufactured and certified systems.

The existing performance standard requires manufacturers to certify that their products meet the applicable performance requirements in effect at the time of manufacture. Therefore, amendments to the performance standard are generally not retroactive and effective dates implementing the standard are specified in the regulations. Usually, a 1-year effective date is provided in order to allow manufacturers time to adjust manufacturing and assembly of their products under the new or amended regulations. Indeed, it would be unreasonable to require the manufacturer to retrofit or to remanufacture previously produced products because of a change in the standard for equipment that could have a useful life of 20 or more years.

In particular, the performance requirements regarding maximum exposure rate limits (proposed to become maximum AKR limits), established in 1994 (59 FR 26402), and the proposed requirements in § 1020.32(h) for fluoroscopic timers are requirements or performance features that users of older fluoroscopic equipment may wish to implement on their systems. The earlier amendment in 1994 and the current proposal apply to new equipment manufactured after the effective date of the amendment. The language proposed for inclusion in § 1020.32(d) and (h) would provide a mechanism for users of older equipment to obtain the performance required under the proposed amendments. These changes would allow older systems to be modified to meet the maximum AKR limit and fluoroscopic timer performance that will be required under the proposed requirements.

The owner of the fluoroscopic system modified under § 1020.30(q) is responsible for assuring that the modified x-ray system complies with the applicable requirements of the performance standard following the modification. The modification to the system may be accomplished by a third party or by the original equipment manufacturer. The system owner, however, is responsible for assuring,

through contract requirements with the party performing the modification or through testing, that the modified system complies with the standard following the modification.

N. Modification of Warning Label (§ 1020.30(j))

FDA proposes to modify the language of the warning label required by § 1020.30(j). The current statement warns that safe exposure factors and operating instructions must be followed. FDA proposes to modify the warning label statement by adding the phrase “maintenance schedules.” This addition incorporates the suggestion of the TEPRSSC and further emphasizes the need for diagnostic x-ray systems to be properly maintained and calibrated. Manufacturers of diagnostic x-ray systems are required under § 1020.30(h)(1)(ii) to provide a schedule of the maintenance necessary to keep the equipment in compliance with the performance standard. The standard places no requirement on owners or users of diagnostic systems to properly maintain these systems. However, the revised wording of the warning label is intended to alert users and facility administrators of the need to properly maintain the systems.

O. Corrections of § 1020.31(f)(3) and (m)

FDA proposes to correct oversights in § 1020.31(f)(3) and (m) that occurred when the July 2, 1999, amendment was published. Section 1020.31(f)(3) addresses the x-ray field limitation requirement for mammographic x-ray systems and § 1020.31(m) addresses the primary barrier required for mammographic x-ray systems. Prior to September 30, 1999 (the effective date of the final rule), the heading to § 1020.31(m) was “Transmission limit for image receptor supporting devices used for mammography.”

When an existing radiation safety performance standard is amended, the new or modified requirement applies only to products that are manufactured after the effective date of the amendment. Normally, the requirement that existed prior to the amendment is retained in the Code of Federal Regulations (CFR) to provide a record of the requirements of the standard applicable to products on their date of manufacture. When the final rule amending § 1020.31(f)(3) and (m) was published on July 2, 1999, the provisions describing the requirements for equipment manufactured prior to September were inadvertently omitted. Thus, the CFR (21 CFR part 1020) has no record of the requirements imposed by § 1020.31(f)(3) and (m) for equipment manufactured between the initial effective dates for § 1020.31(f)(3) and (m) and September 30, 1999. To correct this oversight, FDA proposes to reinstate the provisions describing the requirements that apply to equipment manufactured prior to September 30, 1999, under the earlier versions of § 1020.31(f)(3) and (m). This correction will provide a record of the requirements applicable before September 30, 1999, and close the gap that exists as a result of the oversight in the publication of the final rule.

Additionally, further review of this issue revealed that the original publication of § 1020.31(f)(3) in 1977 (42 FR 44230) did not indicate an effective date for this paragraph, which was November 1, 1977. FDA proposes to insert the omitted effective date. The omission was of little consequence because the original requirement reflected the then current designs of mammographic systems. FDA proposes to insert the date to provide an accurate record of the applicable x-ray field limitation requirements as a function of the date of manufacture of mammographic x-ray systems.

No changes in the previously applicable or current requirements are proposed or intended by these corrections to § 1020.31(f)(3) and (m). The corrections are only intended to make explicit the current or previously applicable requirements that existed on the date of manufacture.

FDA proposes to revise § 1020.31(f) by adding § 1020.31(f)(3)(i), the requirement applicable to equipment manufactured on or after November 1, 1977, and before September 30, 1999. The current requirement, applicable to equipment manufactured after September 30, 1999, would be § 1020.31(f)(3)(ii). Section 1020.31(f)(3)(iii) would contain the requirement for permanent markings that are applicable to all equipment manufactured after November 1, 1977.

FDA proposes to amend § 1020.31(m). Section 1020.31(m)(1) would be revised to contain the requirement applicable to systems manufactured on or after September 5, 1978, and before September 30, 1999; such requirement was previously omitted. Section 1020.31(m)(2) would be revised to contain the current requirements applicable to equipment manufactured after September 30, 1999, in § 1020.31(m)(2)(i), (m)(2)(ii), (m)(2)(iii), and (m)(2)(iv). Section 1020.31(m)(3) would be revised to contain the description of the method for measuring compliance; such description is common to both § 1020.31(m)(1) and (m)(2). A minor technical clarification is also proposed in § 1020.31(m)(2)(ii) where the term “x-ray tube” found in current § 1020.31(m)(2) is replaced by the term “x-ray system” to reflect the fact that it is the x-ray system, not the x-ray tube, that controls initiation of x-ray exposure. This change does not change the intent or effect of the requirement.

P. Corrections to Reflect Changes in Organizational Name, Address, and Law (§ 1020.30(c), (d), and (q))

FDA proposes to amend §1020.30(c) to reflect the current organizational title of the Office of Compliance of the Center for Devices and Radiological Health. FDA also proposes in § 1020.30(d) to remove the specific address that is subject to change from time to time. Additionally, FDA proposes to amend paragraph § 1020.30(q) to reflect the transfer of sections 358(a)(5) and 360B(b) of the PHS Act to the act by the SMDA.

Q. Removal of Reference to Special Attachments for Mammography

FDA proposes to remove reference to “special attachments for mammography” in § 1020.31(d) and (e). The Mammography Quality Standards established in part 900 (21 CFR part 900), particularly § 900.12(b)(1), require that only diagnostic x-ray systems designed specifically for mammography be used to perform mammography in the United States. Therefore, the use of special attachments intended for use with general-purpose diagnostic x-ray systems to perform mammography is inappropriate. No such devices may continue to be used, and retaining this reference in the standard would imply that such devices or components were acceptable.

R. Change to the Applicability Statement for § 1020.32

FDA proposes in the applicability statement of § 1020.32 to remove the reference to “fluoroscopy” and replace it with “fluoroscopic imaging” and to remove “recording of images through an image intensifier tube” and replace this reference with “radiographic imaging when the radiographic images are recorded from the fluoroscopic image receptor.” This change is necessary to clarify the applicability of this section and to incorporate the proposed requirements addressing the production of radiographic images for the last image hold feature.

S. Republication of §§ 1020.30, 1020.31, and 1020.32

Because of the large number of proposed changes in §§ 1020.30,

1020.31, and 1020.32, FDA is republishing these entire sections, including the proposed amendments, rather than publishing only the proposed individual changes to these sections. Although some of the paragraphs in these sections are not changed by this proposal, republication of the entire sections will result in a more reader-friendly version when the final regulation is published.

III. Proposed Effective Date

FDA proposes that any final rule based on this proposal become effective 1 year after the date of publication of the final rule in the
Federal Register
.

IV. Environmental Impact

The agency has determined under 21 CFR 25.30(i) and 25.34(c) that this action is of a type that does not individually or cumulatively have a significant effect on the human environment. Therefore, neither an environmental assessment nor an environmental impact statement is required.

V. Paperwork Reduction Act of 1995

A. Summary

This proposed rule contains information collection provisions that are subject to review by OMB under the Paperwork Reduction Act of 1995 (PRA) (44 U.S.C. 3501-3502). A description of these provisions is given in the following paragraphs with an estimate of the annual reporting and recordkeeping burden. Included in the estimate is the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing each collection of information.

The information collection burden of the current performance standard is covered by an existing information collection clearance, OMB control number 0190-0025. FDA is seeking new information collection clearance for proposed §§ 1020.30(h)(5) and (6), and 1020.32(j)(4).

FDA invites comments on: (1) Whether the proposed collection of information is necessary for the proper performance of FDA's functions, including whether the information will have practical utility; (2) the accuracy of FDA's estimate of the burden of the proposed collection of information, including the validity of the methodology and assumptions used; (3) ways to enhance the quality, utility, and clarity of the information to be collected; and (4) ways to minimize the burden of the collection of information on respondents, including through the use of automated collection techniques, when appropriate, and other forms of information technology.

Performance Standard for Diagnostic X-Ray Systems and their Major Components (21 CFR 1020.30 and 1020.32 amended)

Description
: FDA is proposing to amend the performance standard for diagnostic x-ray systems by establishing, among other things, requirements for several new equipment features on all new fluoroscopic x-ray systems. In the current performance standard, § 1020.30(h) requires that manufacturers provide to purchasers of x-ray equipment, and to others upon request, manuals or instruction sheets that contain technical and safety information. This required information is necessary for all purchasers (users of the equipment) to have in order to safely operate the equipment. Section 1020.30(h) currently describes the information that must be provided.

The proposed rule would add to § 1020.30(h) paragraphs (5) and (6) describing additional information that would need to be included in these manuals or instructions. In addition, proposed § 1020.32(j)(4) would specify additional descriptive information to be included in the user manuals for fluoroscopic x-ray systems required by § 1020.30(h). This additional information would be descriptions of features of the x-ray equipment required by the proposed amendments and information determined to be appropriate and necessary for safe operation of the equipment.

Description of Respondents
: Manufacturers of fluoroscopic x-ray systems that introduce fluoroscopic x-ray systems into commerce following the effective date of the proposed amendments. FDA estimates the burden of this collection of information as follows:

Table 4.—Estimated Average Annual Reporting Burden for the First Year
1

21 CFR Section
No. of Respondents
Annual Frequency per Respondent
Total Annual Responses
Hours per Response
Total Hours

1020.30(h)(5) and (h)(6) and 1020.32(j)(4)
20
10
200
180
36,000

1
There are no capital costs or operating and maintenance costs associated with this collection of information.

Table 5.—Estimated Average Annual Reporting Burden for Second and Following Year
1

21 CFR Section
No. of Respondents
Annual Frequency per Respondent
Total Annual Responses
Hours per Response
Total Hours

1020.30(h)(5) and (h)(6) and 1020.32(j)(4)
20
5
100
180
18,000

1
There are no capital costs or operating and maintenance costs associated with this collection of information.

B. Estimate of Burden

As described in the assessment of the cost impact of the proposed amendment (Ref. 33), it is estimated that there are about 20 manufacturers of fluoroscopic x-ray systems who market in the United States. Each of these manufacturers is estimated to market about 10 distinct models of fluoroscopic x-ray systems. Immediately following the effective date of the proposed amendments, for each model of fluoroscopic x-ray system that manufacturers continue to market, each manufacturer would have to supplement the user instructions to include the additional information required by the proposed amendments.

Manufacturers already develop, produce, and provide x-ray system user manuals or instructions containing the information necessary to operate the systems, as well as the specific information required to be provided by the existing standard in current § 1020.30(h). Therefore, it is assumed that no significant additional capital,

operating, or maintenance costs will occur to the manufacturers in connection with the provision of the newly required information. The manufacturers already have procedures and methods for developing and producing the user's manuals, and the additional information required by the proposed requirements is expected to only add a few printed pages to these already extensive manuals or documents.

The burden that will occur to manufacturers from the new requirements for information in the user's manuals will be the effort required to develop, draft, review, and approve the new information. The information or data to be contained within the new user instructions will already be available to the manufacturers from their design, testing, validation, or other product-development documents. The burden will consist of gathering the relevant information from these documents and preparing the additional instructions from this information.

It is estimated that about 3 weeks of professional staff time (120 hours) would be required to gather the required information for a single model of an x-ray system. It is estimated that an additional 6 weeks (240 hours) of professional staff time would be required to draft, edit, design, layout, review, and approve the new portions of the user's manual or information required by the proposed amendments. Hence FDA estimates a total of 360 hours to prepare the new user information that would be required for each model.

For a given manufacturer, FDA anticipates that every distinct model of fluoroscopic system will not require a separate development of this additional information. Because it is thought highly likely that several models of fluoroscopic x-ray systems from a given manufacturer will share common design aspects, it is anticipated that similar means for meeting the proposed requirement for display of exposure time, air kerma rate, and cumulative air kerma and the requirement for the last-image-hold feature will exist on multiple models of a single manufacturer's products. Such common design aspects for multiple models will reduce the burden on manufacturers to develop new user information. Hence the average time required to prepare new user information for all of a manufacturer's models will be correspondingly reduced. It is assumed that the applicability of the new user information developed to multiple models will reduce the average burden from the 360 hours to about 180 hours per model under the assumption that each set of user information for a given equipment feature design will be a applicable to at least two different models of a manufacturer's fluoroscopic systems. Under this assumption, the total estimated time for preparing the new user information that would be required is 36,000 hours, as shown in table 4 of this document.

In each succeeding year the burden will be less, as the reporting requirement will apply only to the new models developed and introduced by the manufacturers in that specific year. FDA assumes that every two years each manufacturer will replace each of its models with a newer model requiring new user information. The multiple system applicability of this information is accounted for by also assuming that each new model only requires 180 hours of effort to develop the required information. These assumptions result in an estimated burden of 18,000 hours for each of the years following the initial year of applicability of the proposed amendments, as shown in table 5 of this document.

In compliance with the PRA (44 U.S.C. 3507(d)), the agency has submitted the information collection provisions of this proposed rule to OMB for review. Interested persons are requested to send comments regarding information collection to the Office of Information and Regulatory Affairs, OMB (see
ADDRESSES
).

VI. Analysis of Impacts

A. Introduction

FDA has examined the impacts of this proposed rule under Executive Order 12866, the Regulatory Flexibility Act (5 U.S.C. 601-612), and the Unfunded Mandates Reform Act of 1995 (Public Law 104-4) (UMRA). Executive Order 12866 directs agencies to assess all costs and benefits of available regulatory alternatives and, when regulation is necessary, to select regulatory approaches that maximize net benefits (including potential economic, environmental, public health and safety, and other advantages; distributive impacts; and equity). The agency believes that this proposed rule is consistent with the regulatory philosophy and principles identified in the Executive order. In addition the proposed rule is economically significant under Executive Order 12866 and is major under the Congressional Review Act. Therefore the proposal is subject to review under the Executive order.

The Regulatory Flexibility Act requires agencies to analyze regulatory options that would minimize any significant impact on small entities. An analysis of available information suggests that costs to small entities are likely to be significant, as described in the following analysis. FDA believes that this proposed regulation will likely have a significant impact on a substantial number of small entities, and it conducted an initial regulatory flexibility analysis (IRFA) to ensure that any such impacts were assessed and to alert any potentially impacted entities of the opportunity to submit comments.

Section 202(a) of the UMRA requires that agencies prepare a written statement of anticipated costs and benefits before proposing any rule that may result in an expenditure by State, local, and tribal governments, in the aggregate, or by the private sector, of $100 million in any one year (adjusted annually for inflation). The UMRA does not require FDA to prepare a statement of costs and benefits for the proposed rule because the proposed rule is not expected to result in any 1-year expenditure that would exceed $100 million adjusted for inflation. The current inflation-adjusted statutory threshold is about $110 million.

The agency has conducted preliminary analyses of the proposed rule, including a consideration of alternatives, and has determined that the proposed rule is consistent with the principles set forth in the Executive order and in these statutes. The costs and benefits of the proposed rule have been assessed in two separate preliminary analyses that are described in section VI of this document and that are available at the Dockets Management Branch (see
ADDRESSES
) for review. As reviewed below, these preliminary analyses have an estimated upper limit to the annual cost of $30.8 million during the first 10 years after the effective date of the proposed amendments. The analysis of benefits projects an average annual amortized pecuniary savings in the first 10 years after the effective date of at least $320 million, with an estimated 90 percent confidence interval spanning a range between $88.35 million and $1.160 billion. FDA believes this analysis of impacts complies with Executive Order 12866, and that the proposed rule is a significant regulatory action as defined by the Executive order. Because of the preliminary nature of these cost and benefit analyses and estimates, FDA requests comments on any aspect of their methodologies, assumptions, and projections. Comments may be

submitted to the Dockets Management Branch (see
ADDRESSES
).

B. Objective of the Proposed Rule

The primary objective of the proposed rule is to improve the public health by reducing exposure to and detriment associated with unnecessary ionizing radiation from diagnostic x-ray systems, while maintaining the diagnostic quality of the images. The proposed rule would meet this objective by requiring features on newly manufactured x-ray systems that physicians may use to minimize unnecessary or unnecessarily large doses of radiation that could result in adverse health effects to patients and health care personnel. Such adverse effects from x-ray exposure can include acute skin injury and an increased potential for cancer or genetic damage. The secondary objectives of this proposed rule are to bring the performance standard up to date with recent and emerging technological advances in the design of fluoroscopic x-ray systems and to assure appropriate radiation safety for these designs. The proposed amendments would also align the performance standard with performance requirements in current international standards that were developed since the original publication of the performance standard in 1972. In several instances, the international standards contain more stringent requirements on aspects of system performance than the current U.S. performance standard. The proposed changes would ensure that the different safety standards are harmonized to the extent that systems meeting one standard will not be in conflict with the other. Such harmonization of standards lessens the regulatory burdens on manufacturers desiring to market systems in the global market.

The proposed amendments would require particular x-ray equipment features reducing unnecessary radiation exposure and thereby yielding net benefits. The amendments are necessary because the market will not ensure that these equipment features will be adopted without a government mandate for such features. Purchasers in health care organizations have no incentive to demand the more expensive x-ray equipment that would be required by these new amendments because they perceive no institutional economic advantage in doing so as benefits accrue mainly to patients. Furthermore, purchasers are more responsive to physician attention to an immediate need for diagnostic and interventional efficacy from the equipment than to a prospective capability to reduce radiation-associated risk to patients many years in the future. Patients, also focused on their immediate medical needs, will not demand this equipment because they lack information and knowledge about long-term radiation risk and about the highly technical nature of x-ray equipment. Hence these proposed amendments are necessary to realize the net benefits described in the following analysis.

C. Risk Assessment

The risks to health that will be addressed by these amendments are the adverse effects of exposure to ionizing radiation that can result from procedures utilizing diagnostic x-ray equipment. These adverse effects are well known and have been extensively studied and documented. They are generally categorized into two types—“deterministic” and “stochastic.” Deterministic effects are those that occur with certainty in days or weeks or months following irradiation whose cumulative dose exceeds a threshold characteristic of the effect. Above the threshold, the severity of the resulting injury increases as the radiation dose increases. Examples of such effects are the development of cataracts in the lens of the eye and skin “burns.” Skin is the tissue that often receives the highest dose from external radiation sources such as diagnostic or therapeutic x-ray exposure. Depending on the magnitude of the dose, skin injuries from radiation can range in severity from reddening of the skin and hair loss to more serious burn-like effects including localized tissue death that may require skin grafts for treatment or may result in permanent impairment. Stochastic effects are those that do not occur with certainty, but if they appear, they generally appear as leukemia or cancer one or several decades after the radiation exposure. The probability of the effect occurring is proportional to the magnitude of the radiation dose in the tissue.

The primary risk associated with radiation is the possibility of patients developing cancer years after exposure, and the magnitude of this cancer risk is generally regarded to increase with increasing radiation dose. Consistent with the conservative approach to risk assessment described by the National Council on Radiation Protection and Measurements (Ref. 32), we assume a linear relationship between cancer risk and dose. The slope of this relationship depends on age at exposure and on gender. Our benefits analysis presented in section VI.H is based on linear interpolations of cancer-mortality risk per dose derived from BEIR V table 4-3 (Ref. 22) values reduced by a dose-rate effectiveness factor of 2 for solid cancers (Ref. 30). The values used in our analysis are represented in the following graph in figure 1 of the excess lifetime-probability for death per dose associated with radiation exposure.

BILLING CODE 4160-01-S

EP10DE02.058

BILLING CODE 4160-01-C

FDA underscores the overarching uncertainty in these projections with the following statement adopted from CIRRPC Science Panel Report No. 9 (Ref. 30):

The estimations of radiation-associated cancer deaths were derived from linear extrapolation of nominal risk estimates for lifetime total cancer mortality from doses of 0.1 Sv. Other methods of extrapolation to the low-dose region could yield higher or lower numerical estimates of cancer deaths. At this time studies of human populations exposed at low doses are inadequate to demonstrate the actual level of risk. There is scientific uncertainty about cancer risk in the low-dose region below the range of epidemiologic observation, and the possibility of no risk cannot be excluded.

We project that the equipment features that would be required by three of the proposed amendments will promote the bulk of radiation dose reduction and hence cancer risk reduction: (1) Displays of radiation time, rate, and dose values; (2) more filtration of lower-energy x rays; and (3) improved geometrical efficiency of the x-ray field achieved through tighter collimation. We assume that the display amendment would reduce dose on the order of 16 percent. This assumed value is one-half of a 32 percent dose reduction observed for several x-ray modalities in the United Kingdom (UK) between 1985 and 1995. We assume that one-half of the UK dose reduction was due to technology improvements alone, whereas the other half stemmed from the quality assurance use of reference dose levels and patient dose evaluation. The 16 percent dose reduction that we project for the display amendment thus presumes facility implementation of a quality assurance program making use of the displayed values. This analysis and other assumptions—6 percent dose reduction for the filtration amendment, 1 to 3 percent dose reduction for the collimation amendment—are detailed in Ref. 29. We invite comment on these assumptions.

Until recently, the principle radiation detriment for patients undergoing x-ray procedures was the risk of inducing cancer and, to a lesser extent, heritable genetic malformations. Since 1992, however, approximately 80 reports of serious radiation-induced skin injury associated with fluoroscopically-guided interventional therapeutic procedures have been published in the medical literature or reported to FDA. Many of these injuries involved significant morbidity for the affected patients. FDA's experience with reports of such adverse events leads the agency to believe that the number of these injuries is very likely underreported, given the total number of interventional procedures currently performed. Additionally, there is the lack of any clearly understood requirement or incentive for health care facilities to report such injuries. With the advance of fluoroscopic technology and the proliferating use of interventional procedures by practitioners not traditionally specializing in the field, and therefore not completely familiar with dose-sparing techniques, FDA expects an increasing risk of radiation burns that warrants the changes to the x-ray equipment performance standard through the proposed amendments.

D. Constraints on the Impact Analysis

It is FDA’s opinion that the proposed amendments would offer public health benefits that warrant their costs. However, the agency has had difficulty thus far accessing pertinent information from stakeholders to help quantify the impact of the proposal and alternatives. In view of the limited information available with which to develop estimates of the costs and benefits, FDA solicits comments, data, and opinions as to whether the potential health benefits of the proposed amendments would justify their costs. FDA will use all information and comments received to revise the impact assessment in reaching a final determination as to the appropriateness of the proposed amendments.

The principal costs associated with the proposed amendments would be the increased costs to manufacturers to produce equipment that will have the features required by the amendments. FDA has made an estimate of potential cost. The cost estimate is based on a number of assumptions designed to assure that the potential cost is not underestimated. FDA anticipates that the actual costs of these amendments to be significantly less than the upper-limit estimate developed. Manufacturers of diagnostic x-ray systems are urged to provide detailed comments on the anticipated costs of these amendments that will enable refinement of these cost estimates.

The benefits that are expected to result from these amendments are reductions in acute skin injuries and radiation-induced cancers. The proposed amendments would have two types of impact that reduce patient dose and associated radiation detriment without compromising image quality.

The first type of change involves several newly required equipment features that would directly affect the intensity or size of the x-ray field. These are the requirements addressing x-ray beam quality, x-ray field limitation, limits on maximum radiation exposure rate, and MSSD for mini C-arm fluoroscopic systems. Almost all of the changes that directly affect x-ray field size or intensity would bring the performance standard requirements into agreement with existing international voluntary standards. To the extent that these requirements are included in voluntary standards that have a growing influence in the international marketplace, the radiological community has already recognized their benefit and appropriateness. Moreover, harmonization within a single international framework would obviate the expense for manufacturers to produce more than one line of products for a single global marketplace.

The second type of change that would be required by these amendments involves the information to be provided by the manufacturer or directly by the system itself that may be utilized by the operator to more efficiently use the x-ray system and thereby reduce patient dose. There is wide support for and anticipation of these new features by many knowledgeable users of fluoroscopic systems. Similar requirements were recently included in a new international voluntary standard.

E. Baseline Conditions

The cost of the proposed amendments to the x-ray equipment performance standard would be borne primarily by manufacturers of fluoroscopic systems. The cost for one of the nine proposed amendments would also affect manufacturers of radiographic equipment and is discussed in detail in Ref. 28. Therefore, this discussion will focus primarily on fluoroscopy (i.e., the process of obtaining dynamic, real-time images of patient anatomy).

X-ray imaging is used in medicine to obtain diagnostic information on patient anatomy and disease processes or to visualize the delivery of therapeutic interventions. X-ray imaging almost always involves a tradeoff between the quality of the images needed to do the imaging task and the magnitude of the radiation exposure required to produce the image. Difficult imaging tasks may require increased radiation exposure to produce the images unless some significant technological change provides the needed image quality. Therefore, it is important that users of x-ray systems have information regarding the radiation exposures required for the images that are being produced in order to make the appropriate risk-benefit decisions.

Equipment meeting the new standards in the proposed amendments would provide image quality and diagnostic information identical to equipment

meeting current standards. Therefore, the clinical usefulness of the images provided would not change. The amendments would not affect the delivery of x-ray imaging services because the reasons for performing procedures, the number of patients having procedures, and the manner in which procedures are scheduled and conducted would not be changed as a result of the amendments. In addition, nothing in these amendments would adversely affect the clinical information or results obtained from these procedures. These amendments would result in x-ray systems having features that automatically provide for more efficient use of radiation or features that provide the physicians using the equipment with immediate information related to patient dose, thus enabling more informed and efficient use of radiation. These amendments would provide physicians using fluoroscopic equipment with the means to actively monitor patient radiation doses and minimize unnecessary exposure or avoid doses that could result in radiation injury.

Estimates of the annual numbers of certain fluoroscopic procedures performed in the United States during the years 1996 or 1997 were developed, as described in Ref. 29, using data from several sources. These estimates of the annual numbers of specific procedures were used in the estimates of benefit from the proposed amendments. No attempt was made to account for changes in the annual numbers of procedures in future years, due to the large uncertainties in making such projections. FDA also estimates that over 3 million fluoroscopically guided interventional procedures are performed each year in the United States. These procedures are described as “interventional procedures” because they accomplish some form of therapy for patients, often as an alternative to more invasive and risky surgical procedures. Interventional procedures may result in patient radiation doses in some patients that approach or exceed the threshold doses known to cause adverse health effects. The high doses occur because physicians utilize the fluoroscopic images throughout the entire procedure, and such procedures often require exposure times significantly longer than conventional diagnostic procedures to guide the therapy.

FDA records indicate that about 12,000 medical diagnostic x-ray systems are installed in the United States each year. Of these, 4,200 are fluoroscopic system installations. The proposed amendments would apply only to those new systems manufactured after the effective date, therefore affecting the 4,200 new fluoroscopic systems installed annually and a small fraction of radiographic systems that do not currently meet the proposed standard for x-ray beam quality.

In modeling the x-ray equipment market in the United States for the purpose of developing estimates of the cost of these amendments, FDA estimates that there are approximately a total of 40 manufacturers of diagnostic x-ray systems in the United States and half of these (20) market fluoroscopic systems and radiographic systems. It is assumed that manufacturers of radiographic systems typically market 20 models of radiographic systems, while manufacturers of fluoroscopic systems market 10 different models of fluoroscopic systems.

F. The Proposed Amendments

As described in section II of this document, the proposed regulations may be considered as nine significant amendments to the current performance standard for diagnostic x-ray systems and other minor supporting changes to the standard. The nine principal amendments may be grouped into three major impact areas: (1) Amendments requiring changes to equipment design and performance that would facilitate more efficient use of radiation and provide means for reducing patient exposure, (2) amendments improving the use of fluoroscopic systems through enhanced information to users, and (3) amendments facilitating the application of the standard to new features and technologies associated with fluoroscopic systems.

Amendments requiring equipment changes include changes in x-ray beam qual

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A02-30550. Public record. Not legal advice.