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Federal Register / Vol. 86, No. 156 / Tuesday, August 17, 2021 / Proposed Rules
Radiation that was established by NAS
for the purpose of advising the U.S.
government on the relationship between exposure to ionizing radiation and human health. 28 The BEIR VII report focused on health effects from low doses of radiation below 10 rem or 100
mSv 29 and updated the findings of the previous report of low dose radiation, the 1990 BEIR V.
The BEIR VII committee analyzed epidemiologic data and biological data, including a study of the survivors of the Hiroshima and Nagasaki atomic bomb attacks and studies of cancer in children. The BEIR VII committee found that the preponderance of information indicates that there will be some risk, even at low doses and that there is no compelling evidence to indicate a dose threshold below which the risk of tumor induction is zero. 30 The BEIR VII
committee further found when the complete body of research on this question is considered, a consensus view emerges. This view says that the health risks of ionizing radiation, although small at low doses, are a function of dose. 31 The BEIR VII
committee concluded that current scientific evidence is consistent with the hypothesis that there is a linear, nothreshold dose-response relationship between exposure to ionizing radiation and the development of cancer in humans. 32
Following the publication of BEIR V, the NCRP updated its radiation protection recommendations in its 1993
report, NCRP Report No. 116, Limitation of Exposure to Ionizing Radiation. Although the NCRP
acknowledged that it could not exclude the possibility of no health risk from low doses, the NCRP expressed its reliance on the LNT model as the basis for several of its recommendations, Based on the hypothesis that genetic effects and some cancers may result from damage to a single cell, the Council assumes that, for radiation-protection purposes, the risk of stochastic effects is proportional to dose without threshold, throughout the range of dose and dose rates of importance in routine radiation protection. Furthermore, the probability of response risk is assumed, for 28 Id.,
at vii.
its report, the BEIR VII committee defined low dose as doses in the range of near zero up to about 100 mSv 0.1 Sv of low-linear energy transfer radiation. NAS BEIR VII at 2. The NCRP
has considered a very low dose to be a dose below 1 rem or 10 mSv. NCRP, Implications of Recent Epidemiologic Studies for the Linear Nonthreshold Model and Radiation Protection, Commentary 27 April 24, 2018, at 66.
30 NAS BEIR VII at 10.
31 Id.
32 Id., at 323.

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radiation protection purposes, to accumulate linearly with dose.33

In 2001, the NCRP published Report No. 136, Evaluation of the LinearNonthreshold Dose-Response Model for Ionizing Radiation, which reported the work of the NCRPs Scientific Committee 16. Scientific Committee 1
6 was charged with reassessing the weight of scientific evidence for and against the linear-nonthreshold doseresponse model, without reference to policy implications. 34 The NCRP
Report No. 136 explained that the existence of the LNT model for low radiation doses must be extrapolated from data showing adverse health effects from high radiation doses and that there were differing sets of data that both showed evidence for and against the LNT model. Nevertheless, the NCRP
noted that radiation imparts its energy to living matter through a stochastic process, such that a single ionizing track has a finite probability of depositing enough energy in traversing a cell to damage a critical molecular target within the cell, such as DNA. 35 After a comprehensive review of many studies, the NCRP concluded that although other dose-response relationships for the mutagenic and carcinogenic effects of low-level radiation cannot be excluded, no alternate dose-response relationship appears to be more plausible than the linear-nonthreshold model on the basis of present scientific knowledge. 36
In a May 2017 article published in the International Journal of Radiation Biology, the NCRPs president, Dr.
John D. Boice, Jr., supports the continued use of the LNT model. Dr.
Boice states that the LNT model, at least at the current time, has been useful in radiation protection, e.g., a safety culture exists that encompasses the principle of as low as reasonably achievable ALARA considering financial and societal issues, and in this context, notes that worker exposures have dropped dramatically 33 NCRP, Limitation of Exposure to Ionizing Radiation, Report No. 116 1993, at 10 emphasis in the original.
34 NCRP, Evaluation of the Linear-Nonthreshold Dose-Response Model for Ionizing Radiation, Report No. 136 2001, at 1.
35 Id., at 208.
36 Id., at 7. See also id., at 4849 The NCRP also stated therefore, if radiation-induced cancer results directly from the induction of mutations involved in the oncogenic pathway, the data reported do not support the existence of a threshold.; and id., at 77 The NCRP also noted that the majority of studies report linear doseresponse relationships in the lower dose range with the coefficient being quite similar to the alpha coefficient of the in vitro linear-quadratic doseresponse curves..

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over the years. 37 Given that epidemiological studies may not demonstrate the validity of the LNT
model for low doses below 100 mSv, Dr. Boice further states that the use of the LNT model combined with the technical and professional judgment of a competent regulator provides a prudent basis for the practical purposes of radiological protection. 38 In his conclusion, Dr. Boice emphasized that the LNT model is not an appropriate mechanism to assess radiological risk but is the most appropriate model currently available for a system of radiological protection when coupled with the appropriate regulatory and technical judgment.39
In a study funded by the NRC, the NCRP reevaluated the LNT model based on new studies completed since the publication of NCRP Report No. 136 in June 2001. In April 2018, the NCRP
released Commentary 27, Implications of Recent Epidemiologic Studies for the Linear-Nonthreshold Model and Radiation Protection, which provides a detailed assessment of currently available epidemiological evidence and concludes that the LNT model with the steepness of the dose-response slope perhaps reduced by a DDREF dose and dose rate effectiveness factor factor should continue to be utilized for radiation protection purposes. 40 The Commentary explains that while the LNT model is an assumption that likely cannot be scientifically validated by radiobiologic or epidemiologic evidence in the low-dose range, the preponderance of epidemiologic data is consistent with the LNT assumption, although there are a few notable exceptions. 41 The Commentary concludes that the current judgment by national and international scientific committees is that no alternative doseresponse relationship appears more pragmatic or prudent for radiation protection purposes than the LNT
model on the basis of available data, recognizing that the risk for doses 37 J. Boice, Jr., The linear nonthreshold LNT
model as used in radiation protection: An NCRP
update, International Journal of Radiation Biology, Vol. 93, No. 10 2017, at 1080 Boice.
38 Id.
39 Id., at 1089.
40 NCRP, Implications of Recent Epidemiologic Studies for the Linear Nonthreshold Model and Radiation Protection, Commentary 27 April 24, 2018, at 139. The acronym DDREF refers to the dose and dose-rate effectiveness factor, and is used to extrapolate the risk of cancer induction from high doses received acutely, and thus measurable, to those low doses, which cannot be measured and are the focus of the LNT model. Id., at 20 2223, and 34.
41 Id., at 140.

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