Cancer risks of protracted exposure in the Techa River Cohort using the two-step clonal expansion model.

The solid cancer mortality data in the Techa River Cohort in the Southern Urals region of Russia is analyzed. The cohort received protracted exposure in the 1950s from the release of radioactive material from the Mayak plutonium complex. The Extended Techa River Cohort includes 29849 people who resided along the Techa River between 1950 and 1960 and were followed from January 1, 1950 through December 31, 1999. The analysis is done within the framework of the biologically based two-stage clonal expansion (TSCE) model. It is found that about 2.6% of the 1854 solid cancer deaths can be related to radiation exposure. At age 63, which is the mean age of solid cancer deaths, the excess relative risk (ERR) and excess absolute risk (EAR) are equal to 0.76 Gy-1 (95%CI 0.23; 1.29) and 33.0 (104 PYR Gy)-1 (95%CI 9.8; 52.6) respectively. The change of the ERR with age is investigated in detail and an increase of risk with attained age is observed. Furthermore analyses of stomach and lung cancer risks are presented and the data is tested for possible signs of genomic instability