General Principles of Radiation Protection
For practical reasons, the ICRP adopted in the 1950s a linear no threshold (LNT) dose—response relationship, a model indicating that there will be some risk even at low doses, that has served as a base for radiation protection regulations. While the debat
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General Principles of Radiation Protection
For pragmatic reasons and mostly with the intent of regulation, the ICRP adopted in the 1950s a linear no-threshold (LNT) dose–response relationship—a model indicating that there will be some risk even at low doses—though this hypothesis is still not deemed proven. In the 1990s, the LNT model was modified by a dose-rate effectiveness factor (DDREF), to account for an apparent decrease in the effectiveness of low-LET radiation in causing a biological end-point (e.g., cancer) at low doses and dose rates, compared with observations made at high, acutely delivered doses [1]. Now, several studies suggest a lack of adherence to an LNT response, although the interpretation of the available evidence is controversial. Nonetheless, based on current scientific knowledge, the health effects associated with radiation exposure, i.e., stochastic effects, such as cancers, cannot be unequivocally attributed to radiation exposure [2, 3]. The various plausible dose response relationships between cancer risk and exposure, in the ranges of low and very low doses, are illustrated in Fig. 11.1. They are known as (a) supralinear; (b) linear non-threshold (LNT); (c) linear–quadratic; (d) threshold; and (e) hormetic [3] [“From Sources and Effects of Ionizing Radiation, 2012 Report to the General Assembly with Scientific Annexes, Annex A —Attributing health effects to ionizing radiation exposure and inferring risks, by UNSCEAR, ©2015 United Nations. Reprinted with the permission of the United Nations.”] At moderate and high doses, an increased frequency of occurrence of certain health effects can be confidently attributed to radiation exposure. There is sufficient evidence, knowledge, and scientific consensus regarding causal relationships, to be able to predict relatively accurately tissue reactions and their possible severity from exposures at high doses, and an increased risk of stochastic effects from exposures at moderate doses.
© Springer International Publishing Switzerland 2017 H. Domenech, Radiation Safety, DOI 10.1007/978-3-319-42671-6_11
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152 Fig. 11.1 Various possible dose–response relationships
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General Principles of Radiation Protection
Risk
a b c d
e Absorbed dose
Very low dose
Low dose
Moderate dose
In contrast to moderate and high doses, the confidence substantially decreases at lower doses. At lower doses—100 mGy or less—projections of the absolute number of cancer cases in a population have less and less information value and can be increasingly misleading. Thus, the following hypotheses cannot be convincingly verified or falsified [3] [“From Sources and Effects of Ionizing Radiation, 2012 Report to the General Assembly with Scientific Annexes, Annex A—Attributing health effects to ionizing radiation exposure and inferring risks, by UNSCEAR, ©2015 United Nations. Reprinted with the permission of the United Nations.”]: • The currently observed response in the moderate-dose range can be extrapolated linearly down to zero incremental dose above that from normal natural backg
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