RISK OF DIGESTIVE TRACT CANCER IN THE MAYAK WORKER COHORT

INTRODUCTION: An exposure to occupational radiation affects the risk of mortality from cancer. Digestive tract cancers are the major group of all solid cancers. “Mayak” nuclear plant workers were exposed to protracted external gamma and internal alpha radiation in wide dose range. A cohort study of “Mayak” product association (“Mayak” PA) workers could produce the estimates of radiogenic risk of death from cancer.

METHODS:  Digestive tract cancer mortality (excluding liver cancer) has been analyzed. Workers hired 1948-1982 on main “Mayak” PA facilities were included to the epidemiological analyses using cohort study methodology with 1948-2008 follow-up. Background mortality was modeled in terms of gender, age attained, and smoking status. Poisson regression (Amfit) used to estimate the excess relative risk (ERR). 5 year lagged external and internal cumulative dose categorized to pre-defined strata used to assess the risk.

RESULTS:  The major factors affecting the background risk in the modeled digestive tract cancer mortality were: age, gender and smoking.  The shape of dose-response curve considered to be linear at whole dose range. There was less evidence of linear-quadratic or quadratic model. The lower bounds of 95% confidence intervals of some ERR point estimates under 0.3 Gy appeared to include negative values. However, there was no evidence of nonlinearity in a low dose area. Excess relative risk per 1 Gy of external gamma radiation dose was 0.14 (95%CI 0.06-0.26). There was no significant contribution to the radiation induced excess from the internal dose.

CONCLUSIONS:  The risk of the digestive tract cancer mortality, excluding liver cancer, was significantly increased due to external gamma radiation dose. The contribution of internal alpha radiation dose to the excess risk was not significant. Risk assessment under 0.3 Gy using linear extrapolation in a low dose area has it’s known limitations.