Dynamics of thyroid cancer incidence in Russia following the Chernobyl accident: eco-epidemiological analysis

The paper presents the analysis of thyroid cancer incidence in the territories of Russia most contaminated after the Chernobyl accident. In the work data on incidence in the Bryansk, Kaluga, Orel and Tula regions (5298 thousand persons) are used. Information on incidence has been obtained from regional oncological dispensaries (state health institutions involved in diagnosis and treatment of malignant neoplasms). Altogether, 2599 cases of thyroid cancer are considered from 1982 to 1995. Of them, 62 cases were among children and adolescents and 143 among the population who were children and adolescents at the time of the accident in 1986. The study is performed for both sexes. The work uses the approach based on comparison of distributions of thyroid cancer cases by age at diagnosis and age at exposure. It has been shown that since 1991 the age structure of the incidence has changed significantly with the growing proportion of cases among children and adolescents. The change in the structure occurred due to the radiation factor, specifically as a result of exposure of thyroid to incorporated 131l. A dependence of risk of cancer on age at exposure has been derived. For children of 0-4 years at exposure the risk of induction of radiogenic thyroid cancer is 6-10 times higher than in adults. On the average, the risk coefficient in children and adolescents at the time of exposure is about 3 times higher that in adults. The analysis of time trend in thyroid cancer incidence has shown that the incidence rate observed in the period from 1991 to 1995 in the age groups to 25 years would be expected to be maintained in the near future.