Epidemiologic contributions to radiation risk assessment.

Over the last 60 years epidemiologic radiation studies have largely shifted from identifying the range of detriments from high radiation exposures to quantifying the magnitude and uncertainties of risks in the low-dose range. Similarly, my efforts began with relatively high-dose studies of cohorts from bygone eras: follow-up of children who were treated with x-ray for scalp ringworm, infants whose thymus glands were shrunk by radiation, and women who received x-ray therapy for breast infections. A follow-up study was conducted to estimate cataract risk among clean-up workers after the 1986 Chernobyl nuclear accident. At the Radiation Effects Research Foundation my goals in supervising research on the lifespan study (LSS) of atomic bombing survivors were to stimulate new research initiatives and to provide guidance on methodology and analyses. These included dose-response studies of circulatory diseases and cataract in survivors, and of metabolic and cardiovascular outcomes amongin uterosurvivors and F1offspring. A challenging NCRP committee task was to evaluate the degree of epidemiologic support for a linear nonthreshold model of radiation risk for solid cancer. A public health assessment for UNSCEAR concluded there was little likelihood of future detectable cancer risks from the Fukushima nuclear plant disaster in 2011. A recent ICRP effort has been to develop epidemiologic estimates of the dose rate effectiveness Factor by comparing cancer risk estimates from occupational and environmental radiation studies with mostly low cumulative photon radiation doses and/or low dose-rates (LDLDR) to those derived from the LSS. Continued observation of the Million Person Study and other cohorts exposed to LDLDR radiation has the potential to further improve estimates of potential risks from radiation exposure and should be pursued.