Analysis of thyroid cancer data from the Ukraine after 'Chernobyl' using atwo-mutation carcinogenesis model

The thyroid cancer data of children in the northern regions of the Ukraine after the reactor accident at Chernobyl were combined with thyroid dose mea surements in the same regions and analysed using a two-mutation carcinogene sis model. The best fit was obtained for radiation acting as an initiating agent, i.e. on the first mutation of the model. The observed relatively hig h increase of thyroid cancer incidence after 1990 in children exposed to ra diation released after the reactor accident could be ascribed to the high t hyroid doses and the relatively low background thyroid cancer incidence in children. The maximum annual incidence is predicted to occur fairly soon af ter the reactor accident, i.e. about 10 years. For adults, the predicted re lative increase of annual thyroid cancers is much lower than for children y ounger than 20 years. The modelling results are used to derive risk estimat es for radiation-induced thyroid cancer. These risk estimates are dependent on age at exposure, follow-up time and the background thyroid cancer incid ence. The calculated excess absolute risk for a population of all ages is a bout one-third of that currently used by ICRP, but for children the calcula ted absolute risks are about a factor of 3 higher than derived in other epi demiological studies. The model results indicate that the excess absolute r adiation risk per unit dose for children is about the same as or a little l ower than that for adults.