Aetiological Factors in Thyroid Malignancy - Ionising Radiation (2)

The carcinogenic risk factor has been calculated to be one per cent per 1Gy (l00rad) in 20 years. The latent period is approximately 10 - 20 years, or even longer. Occasional cases have been reported in irradiated adults. 
Therapeutic sterilising doses of radiation to the thyroid (for example radiological treatment of laryngeal carcinoma or 131I treatment of Graves' disease) are not associated with cancer induction; in fact, such patients are liable to develop hypothyroidism.