POSITIVE BEAM LIMITATION REQUIREMENT IS ELIMINATED IN FINAL RULE ON X-RAY SYSTEMS; FDA SETS LIMITS ON EXPOSURE RATE IN PROPOSED FLUOROSCOPY AMENDMENT

The positive beam limitation (PBL) requirement is eliminated from FDA's performance standard for diagnostic x-ray systems and their major components in a final rule published May 3 that makes several modifications to the standard. FDA is removing the PBL requirement despite notable opposition. The agency announced its intent to make PBL optional in an October 1989 proposal for modifications to the x-ray standard ("The Gray Sheet" Oct. 30, 1989, p. 15). The proposal ran counter to the opinion of the agency's technical electronic products radiation safety standards committee (TEPRSSC), which recommended in 1987 that the requirement be retained. In addition, about half of the comments FDA received on the PBL portion of the 1989 proposal opposed the removal of the requirement. Explaining reasons for eliminating PBL in the 1989 proposal, FDA said that the provision was "more than half the cost impact of the entire performance standard." The agency also noted "evidence that the originally anticipated dose saving to be accomplished by PBL could have been accomplished without PBL." In the preamble to the final rule, FDA responds to the comments it received in opposition to the removal of the requirement. For example, some comments said that many facilities do not have well-trained operators, therefore, PBL is needed to guarantee proper collimation. FDA responds that "equipment features cannot substitute for adequately trained personnel," adding that "PBL does not prevent inappropriate use or operation of a system or always guarantee appropriate collimation." Some comments said that if PBL were not required, the systems would disappear from the marketplace due to low demand and high cost. Explaining why it does not agree, FDA says that "many facilities appreciate the speed and convenience provided" by some PBL systems. The amendment "merely recognizes, in some situations, the cost of a PBL may not be justified by the benefit, and FDA will allow alternatives." Two comments speculated on the "assumed motivation" for FDA's proposal, suggesting that the changes were made "due to problems enforcing the performance standard" and that manufacturers, unable to design "reliable" PBL systems, were exerting pressure on FDA for the proposed change. The agency denied these claims, stating that they have "received no pressure to revise the performance standard, although occasional suggestions have been received." FDA continues: "The proposal to amend resulted from an internal review of the effectiveness of the performance standard, in which FDA attempted to provide an objective analysis of the benefits and costs associated with each section of the performance standard. This process involved outside participation through requests for comments and public discussion at an advisory committee meeting." Other modifications to the standard include the deletion of the bulk of the section entitled "Assembly and Reassembly of Diagnostic X-ray Systems." The section outlined requirements regarding the use of certified and uncertified components in the manufacturing or refurbishing process. The removal of this section was outlined in the 1989 proposal. Explaining the elimination of the section in the preamble, FDA notes that the "differences between specifications for certified and uncertified components" in the section "were minor except for the requirement for" PBL on "general purpose radiographic systems." In light of the elimination of the PBL requirement, "this major difference no longer exists," FDA notes. Therefore, the removal of the assembly/reassembly section should not have a large impact. However, FDA is retaining one portion of the assembly/reassembly section that addresses exceptions to report requirements. Specifically, the portion provides guidance on how the requirements for reporting of component assembly are applied during repair. According to FDA, the information is still "relevant," but is "more logically" contained in the "Certification by Assembler" section, where it has been moved in the final rule. One part of the proposal that was not adopted in the final rule is the reduction of the minimum illuminance requirement to 100 lux. Instead, FDA decided to leave the 160 lux requirement unchanged after receiving "compelling" comments. One such comment suggested that with PBLs becoming optional, keeping the requirement of 160 lux would become more important, "since the light field will become the primary means for adjusting the x-ray field size." Also in the proposal, FDA had proposed changing all measurements to the International System of Units (SI). Responding to submitted comments, FDA agreed to retain the use of traditional units in parentheses next to the SI units "to minimize confusion and allow continued use of current instruments." On a related point, FDA dismissed, for the time being, a recommendation to adopt the exposure quantity "air kerma" and its SI unit, the "gray," in order to comply with measurements set forth by the National Council on Radiation Protection and Measurement. FDA asserts that to implement such a change also would require increasing the limits in the standard for exposure rate by approximately 15%. FDA says it will "consider such a change in a future proposal." Also on May 3, FDA published proposed amendments to the x-ray performance standard regarding "the limits established for maximum radiation emission for fluoroscopic x-ray systems during high- level control and other modes of operation." The revisions, which were proposed due to concern regarding the potential for "excessively high" exposure levels, were endorsed by TEPRSSC ("The Gray Sheet" Nov. 19, 1990, p. 9). As it currently stands, the standard has a two-tiered system for limits on entrance exposure rate (EER) for normal fluoroscopy with automatic exposure rate control (AERC). If the system has a high-level mode of operation, the EER limit is 5 roentgens/minute; if it does not, the limit is 10 R/min. In the proposed amendments, FDA replaced the two limits with a single limit of 10 R/min. FDA also says it intends to set a limit on the maximum EER permitted during the high-level control mode. In the existing standard, no limit was established on maximum patient EER in the high-level mode, allowing for exposure rates and high radiation output for which a clinical need "has not been demonstrated," according to FDA. FDA currently proposes to limit the maximum EER to 20 R/min. FDA also proposes that any fluoroscopic system capable of operating at greater than 5 R/min. have an AERC mode of operation. According to FDA, this will free "the physician to concentrate on the clinical aspects of the examination, without concern for equipment technique factors."