25 巻 (2015) 2 号 p. 83-89
This paper will review current radiological protection (RP). Risk concept has been proposed in the light of precautionary principle since 1950's, although RP philosophy has been historically built partly based on scientific evidence. RP uses the risk estimate of cancer obtained by epidemiological studies. Linear-Non-Threshold (LNT) models assume there is some probability no matter how low dose is received, since convinced evidence has not been established on radiation risk at low-dose and low-dose rate. How to apply the risk concept is a key issue in radiological protection. RP introduces three fundamental principles such as justification, optimization and dose limitation. Furthermore, RP uses a situation-based approach where planned, emergency and existing exposure situations are defined. In an existing exposure situation after the Fukushima accident, reference levels can be applied to drive risk reduction using protective actions such as evacuation and foodstuff restriction. The risk concept can explain why the dose limits used in a planned exposure situation should not be applied in terms of risk-tradeoff.