NCRP SCIENTIFIC COMMITTEE 1-14

NCRP SCIENTIFIC COMMITTEE 1-14 ON

PUBLIC DOSE LIMITS FOR IONIZING RADIATION

By Edgar D. Bailey

Earlier this year the National Council on Radiation Protection and Measurements (NCRP) established a new Scientific Committee to prepare an NCRP Statement to address the application of a recommendation contained in NCRP Report No. 116 (Limitation of Exposure to Ionizing Radiation). The recommendation is “that whenever the potential exists for exposure of an individual of the public to exceed 25 percent of the annual effective dose limit as a result of irradiation attributable to a single site, the site operator should ensure that the annual exposure of the maximally exposed individual, from all man-made exposures (excepting that individual’s medical exposure), does not exceed 1 mSv on a continuous basis.” The recommendation continues “Alternatively, if such an assessment is not conducted, no single source or set of sources under one control should result in an individual being exposed to more than 0.25 mSv annually.” This statement was the outgrowth of a similar recommendation contained in NCRP Statement No. 6 (Control of Air Emissions of Radionuclides), which envisioned an individual who might be simultaneously exposed to emissions from more that one source of radioactive air emissions.

Recently there has been a great deal of discussion, as well as some controversy, regarding the applicability of this recommendation, especially in the context of the design of shielding for medical X-ray facilities. Scientific Committee 9, which is preparing a revision of an NCRP shielding report, had included this recommendation in drafts of its report. Reportedly at least one state is already requiring an annual public dose limit of 0.25 mSv in new shielding designs. The health physics and medical physics community had expressed a great deal of concern and apprehension about whether the NCRP annual public dose limit of 1 mSv or 0.25 mSv should be the design objective for new X-ray facilities, and how a change to 0.25 mSv would apply to existing facilities. Due to the (undefined and unevaluated) conservatisms inherent in present shielding evaluations, various individuals have opined that diagnostic X-ray imaging facilities designed to a 1 mSv annual public dose limit would, in fact, actually ensure that no individual would receive an annual effective dose in excess of 0.25 mSv. At the heart of the controversy are the costs associated with the increased shielding and, in many cases, the feasibility of retrofitting existing facilities in the absence of a demonstrated safety need.

Scientific Committee 9 has removed reference to a 0.25 mSv annual limit from the current version of its draft report, leaving the applicability of this recommendation somewhat in limbo.

The purpose of Scientific Committee 1-14 is to clarify the recommendation on the NCRP public dose limit, particularly as it relates to X-ray facilities and other facilities that do not involve releases of radionuclides.

The membership of the committee includes Richard J. Vetter (Chairman), S. James Adelstein, Edgar D. Bailey, Carl J. Paperiello, J. Thomas Payne, R. Julian Preston, Warren K. Sinclair, and Paul Slovic.

The first meeting of the committee was held in Arlington, Virginia, on April 13, 2004, in connection with the 40^th Annual Meeting of the NCRP. At that meeting an aggressive schedule was put forward to prepare a formal NCRP Statement on the issue and the implementation of the recommendation within the next six months. The next meeting of the committee was tentatively scheduled for July 15 and 16, 2004, in Washington, D. C. At that meeting the committee plans to finalize its work on the Statement and submit it for review and approval by the NCRP Council prior to adoption.