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.

Werner Rühm (Chair), Helmholtz Zentrum München, Germany
Tamara Azizova (Member), Southern Urals Biophysics Institute, Russian Federation
Simon Bouffler (Member), PHE, UK
Mark P. Little (Member), National Institutes of Health, USA
Roy E. Shore (Member), New York University School of Medicine, USA
Linda Walsh (Member), University of Zurich, Switzerland
Gayle Woloschak (Member), Northwestern University, USA
Bernd Grosche (Corresponding Member), ex Federal Office for Radiation Protection (BfS), Germany
Michiaki Kai (Corresponding Member), Oita University of Nursing and Health Sciences, Japan
Kotaro Ozasa (Corresponding Member), Radiation Effects Research Foundation, Japan
Kazuo Sakai (Corresponding Member), Tokyo Healthcare University, Japan
Quanfu Sun (Corresponding Member), National Institute for Radiological Protection, China