Thyroid morphological and functional tests were carried out on 396 patients who were recalled because their thyroid gland had been exposed during hemangioma irradiation in childhood 11-43 years before (median, 22 years). The irradiations have been classified into two categories based on their duration: short duration, from a few seconds to a few minutes (<tex-math>${}^{90}{\rm S}$</tex-math> and X rays), and long duration, from 30 min to several hours (<tex-math>${}^{336}{\rm Ra},{}^{192}{\rm Ir}$</tex-math>, and32 P). The risk of a thyroid nodule increased significantly with the total dose received by the thyroid; it was linked to the dose delivered in the short duration (excess relative risk per Gy = 10), but not to that delivered in the long duration. The risk of a simple diffuse goiter, which also increased with the dose received by the thyroid, did not depend on the duration of the irradiation. In conclusion, this study emphasizes the role of the dose rate in the risk of thyroid nodule, the detection of which does not appear to be improved by plasma thyroid marker determination.

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