Task Group 91
Radiation Risk Inference at Low-dose and Low-dose Rate Exposure for Radiological Protection Purposes
The detriment-adjusted nominal risk coefficients recommended by ICRP have been based, to a large extent, on data obtained from the atomic bomb survivors in Japan. Because their exposure was a single acute exposure, and because it was thought that the most plausible biological model for the dose response relationship should be linear quadratic (which implies a larger slope at high doses than a low doses), many international and national relevant bodies, such as UNSCEAR, BEIR and also ICRP have used over the years a Dose and Dose-Rate Effectiveness Factor (DDREF) for estimates of these coefficients at low doses. A value of 2 was used by ICRP for low-dose and low-dose rate exposures, which are typical in radiation protection. With more epidemiological information becoming available and with modern techniques of Bayesian analysis, UNSCEAR has recently re-evaluated all the available information using Bayesian techniques and has estimated risk coefficients that are similar to the ICRP estimates using high doses and a DDREF value of 2. However, in their 2006 report the BEIR committee (BEIR VII) also using a Bayesian approach recommended a DDREF of 1.5.
The Task Group will review the currently available information on the estimation of risk coefficients and recommend:
(1) Whether it is desirable to continue to estimate risk at low doses by assessing the slope of the dose response at high doses and then applying a DDREF reduction factor. The alternative is to adopt the UNSCEAR approach of inferring the risk coefficients at low doses by using all available information and techniques of Bayesian analysis for estimating the best expert judgment.
(2) Whether such coefficients are applicable to acute, protracted and prolonged exposure or need a particular correction.
The Task Group will prepare a position paper including recommendations for further action, for consideration by Committee 1 and the Main Commission.
|Helmholtz Zentrum München, Germany|
|Southern Urals Biophysics Institute, Russian Federation|
|Professor Roy E. Shore|
|Radiation Effects Research Foundation (RERF), Japan|
|Northwestern University, USA|
|Dr Bernd Grosche|
|Federal Office for Radiation Protection (BfS), Germany|
|Dr Michiaki Kai|
|Oita University of Nursing and Health Sciences, Japan|
|Dr Kazuo Sakai|
|National Institute of Radiological Sciences (NIRS), Japan|