On July 25, the Nuclear Regulatory Commission (NRC) published a final policy statement on the protection of cesium-137 chloride (CsCl) Sources. The NRC policy recognizes that the CsCl sources enable three specific classes of applications that benefit society: 1) blood irradiation, 2) biomedical and industrial research, and 3) calibration of instrumentation and dosimetry. Incorporating ASH’s recommendations, the NRC lists hematology and bone marrow transplantation in the biomedical research uses of CsCl sources. The policy also states that although these sources are adequately protected under the current NRC requirements, design improvements could be made that further mitigate or minimize the radiological consequences. The NRC also intends to monitor development of alternative forms of cesium-137.
Most importantly, and as ASH had pointed out, the NRC recognizes that for most research, there are no alternatives to Cs-137 irradiation because of the unique properties of Cs-137 radiation, such as high dose rates with uniform fields of linear energy transfer. No alternative technologies that can effectively replace CsCl sources for biomedical research have yet been developed. Based on decades of use, including trial use of certain x-ray machines for irradiation, the biomedical research community considers the Cs-137 irradiators optimal for providing effective, reliable, dependable, economical, and experimentally reproducible means of required health care equipment needed for research. The NRC policy adopts ASH’s position that the results of previous research with Cs-137 irradiators cannot be compared to results obtained from other types of irradiation due to differences in the energy spectra and dose distribution of the radiation sources. Conversion factors between biomedical experimental results of x-ray versus gamma-rays do not exist. The use of alternative technologies would necessitate extensive research to re-validate research models of diseases that have already been established using irradiation devices containing Cs-137.
The NRC policy also recognizes that blood irradiation is medically essential to prevent transfusion-associated Graft-Versus-Host disease and the vast majority of hospitals use only irradiated blood. The CsCl blood irradiators are used to irradiate over 90 percent of all irradiated blood because CsCl blood irradiators are the most reliable and efficient blood irradiation devices currently available.
ASH is pleased that the NRC staff’s analysis and conclusions echoed the Society’s concerns. ASH thanks all members who participated in developing comments on this important issue.
For more information, additional background on the NRC policy and ASH’s involvement, please click here.
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