Populations Living near the Semipalatinsk Test Site: A New Cohort for Assessing Health Effects from Protracted Exposures to Low-to-moderate Doses of Radiation

Although numerous epidemiological studies have demonstrated an increased risk of cancer and non-cancer diseases associated with acute exposures to high doses of radiation, possible effects of protracted exposures to low-to-moderate doses of radiation remain to be investigated. Several epidemiological studies have been conducted for residents living near the Semipalatinsk Test Site in the former Soviet Union who were exposed to protracted low-to-moderate doses of both external and internal radiations. However, small population size and other limitations of the previous studies preclude a precise evaluation of the health effects. An international joint study of Kazakhstan and Japan was initiated in 2001 to investigate the health effects among residents of the exposed areas based on a new large-scale cohort of the Semipalatinsk populations. In the joint study, information was obtained on the name, date of birth, sex, residential history and vital status of individuals living in the former Semipalatinsk oblast and other exposed areas using archived and official data. By March 2009, data of 131,723 residents were collected, among which the vital status of 41,128 residents (30.7%) was ascertained. The completeness of the ascertainment depended on the place of residence with lower completeness for control areas mainly because of emigration. Although any analysis based on retrospective follow-up data is limited because of potential selection bias, the sub-population of our established cohort will be a useful resource for future prospective studies.