閾値連動型放射線防護のための新ツール

The current system of radiological protection (SRP) is based on the linear no-threshold (LNT) hypothesis for radiation-caused cancer and other forms of health detriment. Now there is overwhelming evidence of a dose-rate-dependent population threshold (abbreviated t) absorbed dose for cancer induction. Thus, the SRP needs to be updated to account for the threshold, and tools for doing so are provided in this article. These tools include the organ/tissue-T-related, threshold{t}-based, equivalent dose H{t}T (e.g., in sieverts), which is evaluated using the threshold-based radiation weighting factor wR,t. A second tool is the population equivalent dose threshold HT,t. When used in radiation exposure limitation, its value is assigned for a reference group, reference organ/tissue characteristics, and reference exposure scenario (high dose rate), so that the equivalent dose limit H{t}T,lim is expressed as H{t}T < H{t}T,lim ≤ HT,t (high dose rate). A third tool is the organ/tissue-specific exceedance equivalent dose "ΔH{t}T= H{t}T- HT,t≥ 0 Sv," which is summed to get the total-body exceedance (TBEX). For many different radiation exposure scenarios, TBEX will be zero (Sv), unlike for the effective dose E. With an updated SRP based on a modern-science-related population threshold dose for radiation-caused health detriment, use of the LNT-based effective dose E and the as low as reasonably achievable principle would no longer be credible.