Appendix 11: Thyroid Cancer Excess Risks in Ukrainian and Belarusian Areas Affected by the Chernobyl Accident

Data are analysed for 684 settlements in Ukraine and 458 settlements in Belarus. In each of the settlements more than 10 measurements of the I content in human thyroids had been performed in the period May/June 1986. Based on the measurement data, average thyroid doses due to the Chernobyl accident were assessed for every birth year in the birth-year cohort 1968-85. Census data from 1979 and 1989, and mortality rates in the period 1986-89 were used to derive the population structure in 1986. Case data were numbers of operations of pathologically confirmed thyroid cancers in the period 1986-2001 taken from registries that include the place of residence at the time of the accident. The excess absolute risk (EAR) per thyroid dose in all 1142 settlements is estimated for females to 3.1 (95% CI: 2.6; 3.6) cases per 10 PY-Gy, and for males to 2.4 (95% CI: 2.0; 2.8) cases per 10 PY-Gy. The excess relative risk (ERR) per dose is for females 7.2 (95% CI: 5.3; 9.1) Gy, and for males 42 (95% CI: 13; 71) Gy. The estimates for Ukraine are significantly lower than for Belarus (p < 0.007). The EAR per dose decreases with increasing age at exposure and increases with time after exposure. The ERR per dose decreases with time after exposure. The results agree within the confidence limits with excess risks that have been reported for external exposures during childhood.