| Abstract |
X-rays and gamma radiation are well-established carcinogens with substantial evidence of carcinogenicity in humans from epidemiological research. In contrast, there is very little epidemiological research on the human health effects of beta radiation. Even less is understood about the effects of chronic exposure to beta-emitters, such as tritium, a low-energy radioisotope of hydrogen that is produced through nuclear fuel production. Radiation protection standards assign a relative biological effectiveness (RBE) of 1 for beta-emitters compared to gamma-emitters. However, a recent scientific review concluded that the RBE of tritium needs reevaluation. The goal of this proposed study was twofold. First, we proposed to estimate the RBE of tritium based on data from the existing literature. The ultimate goal was to apply an accurate RBE for tritium to examine the relationship between chronic, low-dose tritium exposure and cancer among a cohort of nuclear production workers at the Savannah River Site (SRS), the nation's only large-scale tritium production facility. Second, we proposed to utilize the information regarding the RBE of tritium to reevaluate the cancer mortality associated with other forms of radiation exposure in conjunction with tritium at the SRS facility. Worker information, including annual tritium and gamma radiation dose, is enumerated for 18,883 workers employed from 1951-1999. Using this data, we proposed to establish the distribution of the RBE of tritium with gamma as our reference form of radiation. Recognizing that quantification of a dose-response function for the tritium component of SRS workers will be highly imprecise due to the low magnitudes of tritium doses, we employed Markov Chain Monte Carlo estimation, a technique that allowed us to establish an a priori distribution based on data from laboratory studies and to test how well an epidemiologic dataset - the SRS cohort data - fits that distribution. Finally, we use these estimates to provide more accurate evaluation of the relationship between chronic, low-dose radiation exposure and cancer outcomes. The results of the research are relevant for a broad range of occupational and environmental exposures. |
