
<b>Thyroid</b>

The thyroid gland may be inadvertently irradiated while cancer in another structure is being treated. The thyroid is an organ that is usually susceptible to exposure to ionizing radiation, both by virtue of its ability to concentrate radioiodine (internal radiation) and by routine medical usage: Chest Xray, Dental Xray, X-irradiation of cervical lymph nodes etc. (external radiation). Iodine-131 is widely used for the therapy of Graves' disease and thyroid cancers, of which the disadvantage is radiation-induced hypothyroidism but not complications of thyroid tumor. The thyroid gland is comparatively radioresistant, however, the data obtained from Hiroshima, Nagasaki and Marshall islands indicates a high incidence of external radiation-induced thyroid tumors as well as hypothyroidism. The different biological effects of internal and external radiation remains to be further clarified. Interestingly, recent reports demonstrate the increased number of thyroid cancer in children around Chernobyl in Belarus. There was an increased incidence of thyroid dysfunction and thyroid neoplasia when compared to the general population, in children who received neck irradiation for cancer.