Assessment of radiation risks of solid cancer incidence among the liquidators of the Chernobyl accident (the cohort studies for the follow-up period 1986-1996)

The paper provides analysis of information about solid cancer incidence among liquidators of the Chernobyl accident accumulated in the Russian National Medical and Dosimetric Registry (RNMDR) from 1986 to the beginning of 1997. The RNMDR contains individual dosimetric data and results of annual medical examinations of liquidators living in the territory of the Russian Federation (174916 persons by the beginning of 1999). Consideration is given to male liquidators who had no cancer before entering the 30-km zone around the Chernobyl NPP and for whom information was available about date of birth, date of arrival to the zone, duration of stay in the zone and data of medical examinations. The number of liquidators meeting these requirements is 160564, which accounts for about 90% of all liquidators registered in the RNMDR. For most of liquidators (70%) the Registry database contains information on external radiation dose received during their stay in the 30-km zone. The mean dose in this study cohort is 0.1 Gy, the mean age at the time of the first arrival in the zone is 34 years and the total number of accumulated person-years is 1353935. The cohort of liquidators is briefly described and the cancer incidence rates are compared in liquidators and the population of Russia as a whole through calculation of the standardized incidence ratio (SIR). The excess relative risk per unit dose is also estimated (ERR/Gy). The risk values with 95% confidence intervals for all solid malignant neoplasms and cancers of respiratory organs and digestive system are estimated to be 0.91 (0.25; 1.57), 1.13 (-0.24; 2.40) and 0.85 (-0.3; 2.04), respectively.