Risk of thyroid cancer among Chernobyl clean-up workers in Ukraine

OPS 26: Radiation, EMF, cancer and mortality, Room 114, Floor 1, August 26, 2019, 4:30 PM - 5:45 PM Although much is known about the radiation-related risk of thyroid cancer in those exposed at young ages, less is known about the risk due to adult exposure. Among Japanese atomic bomb survivors and in some other higher dose groups there is little or no statistical evidence of a radiation dose-response for thyroid cancer among those exposed in adulthood. In contrast, a strong and significant dose-response was found in a case-control study of Belarusian, Russian and Baltic clean-up workers exposed as a result of the 1986 Chernobyl nuclear power plant accident. To improve the characterization of thyroid cancer risk following adult exposure, we conducted a nested case-control study (149 cases; 458 controls) in Ukrainian clean-up workers. Individual thyroid doses due to external irradiation, inhalation during the cleanup mission, and intake of I-131 during residence in contaminated settlements were calculated for all study subjects (total dose mean 199 mGy; range 0.15 mg to 9 Gy). Our preliminary findings suggest a non-significantly increased total radiation dose-response for thyroid cancer (excess relative risk [ERR] =0.40; 95% confidence interval: -0.05, 1.48; p=0.12). Time since exposure significantly modified this association so that less time since exposure was associated with a higher ERR/Gy. Further analyses are being conducted to characterize the dose-response relationships according to source of exposure and histological subtype.