[Influence of the distribution of the dose on carcinogenic effects of ionizing radiations of low lineal energy transfer on the thyroid tissue]

The frequency of thyroid nodules has been studied among 396 children irradiated for a hemangioma, from 1946 to 1973. 226Ra, 192Ir, 90Y, 32P, 90Sr, as well as X-rays had been used for treatments. The doses of radiation received by the thyroid of each child have been estimated retrospectively. The irradiations have been classified in two categories based on their duration: less than 30 min., and more than 30 min. The doses received with each of these two types of irradiation were summed for each patient. The risk of thyroid nodule increased as a function of the dose to thyroid only for the dose delivered with the short duration. This study emphases the importance of the role of the dose rate in the risk of radio-induced tumour.