Risk of radiogenic thyroid cancer in the population of the Bryansk and Oryol regions of Russia after the Chernobyl accident (1991–1998)

Abstract

The manuscript presents results of the radiogenic thyroid cancer risk analysis in the Bryansk and Oryol regions among children and adolescents at exposure (0–17 years of age). A total of 170 cases of thyroid cancer were diagnosed from 1991 to 1998. Of these, 106 cases were in the Bryansk and 64 in the Oryol region. The size of the exposed population under study is 374 447 persons in the Bryansk region and 207 592 persons in the Oryol region (data of the 1989 census). The mean thyroid dose from incorporated isotopes of 131I for children and adolescents at exposure is 0.071 Gy in the Bryansk region and 0.013 Gy in the Oryol region. The method of maximum likelihood for nonstationary Poisson series of events was used for risk calculation. The analysis focuses on the relationship between thyroid cancer incidence and thyroid dose due to incorporated iodine radioisotopes. The calculations were based on personal data about disease cases and demographic and dose information for the population points in the regions under study. Statistically significant excess of thyroid cancer incidence above the spontaneous rate was obtained for children and adolescents of the Bryansk region. The excess relative risk per unit dose of 1 Gy (ERR1Gy) with 95% confidence intervals is 11.9 (7.2, 16.6). For children and adolescents of the Oryol region between 1991 and 1998 statistically significant excess risk was not detected: 6.5 (−20.2, 30.2). The value of the standardized ratio of spontaneous thyroid cancer incidence in the region to the general incidence in Russia is 3.5 with 95% confidence intervals (2.8, 4.2) for the Bryansk region. For the Oryol region this ration is 5.3 (4.0, 6.6). The excess of spontaneous incidence observed in the study areas is primarily due to regional differences in incidence and registration features (screening effect). The attributive risk of induction of radiogenic cancers among children and adolescents in the Bryansk region is 46%. This mean that one of every two thyroid cancers detected in the Bryansk region between 1991 and 1998 are radiation induced. © 2002, Elsevier B.V.