Thyroid cancer incidence among liquidators of the Chernobyl accident. Absence of dependence of radiation risks on external radiation dose.

The increase of thyroid cancer incidence rate among children living in the Chernobyl contaminated territories of Belarus, Russia and Ukraine has widely been accepted. Our current work deals with thyroid cancer incidence in the cohort of liquidators (99024 persons) living in 6 regions of Russia: North-West, Volgo-Vyatsky, Central-Chernozemny, Povolzhsky, North-Caucasus and Urals. In the period 1986-1998, a total of 58 thyroid cancer cases were detected in this cohort. We found a statistically significant increase of the thyroid cancer incidence rate in liquidators as compared to the baseline (male population of Russia) level (SIR=4.33, 95% CI: 3.29; 5.60). It was demonstrated that there is no dependence of incidence rates due to external radiation exposure (ERR/Gy=-2.23, 95% CI: -4.67; 0.22).