Host: The Japan Radiation Research Society
Co-host: Asian Association for Radiation Research
Radiation protection standards rely heavily on data from the A-bomb Survivors, who were exposed primarily to instantaneous low-LET gamma radiation. Applications, however, are typically to chronic exposure to other radiations, such as indoor radon or high-LET internal emitters (e.g., Plutonium). Information on how to extrapolate risk estimates from one type of exposure to another is lacking. The Japanese Thorotrast and Japanese A-bomb Survivor cohorts provide a means to compare risks in effectively similar populations. Both cohorts have been followed for cause of death over many decades, and both cohorts have relatively reliable dosimetry. Restricting the A-bomb survivor cohort to the same gender and ages at time of exposure (males aged 20 to 40) as the Thorotrast cohort, we estimated subsequent risk of total mortality, solid cancer mortality, and liver cancer mortality. Based on 3,397 deaths in the A-bomb Survivor Cohort (207,314 person years) and 1,548 deaths in the Thorotrast Cohort (83,729 person years), the relative risk of death from all causes (exposed versus non-exposed) was 1.06 for the A-bomb cohort (p = 0.13) and 2.3 for the Thorotrast cohort (p < 0.001). Estimates of excess relative risk (ERR) per Gray for total mortality as well as that for death from solid cancer and death from liver cancer will be reported. Modification of the risk of cancer mortality by age at exposure will also be assessed.
