Late morphological and functional changes in thyroid gland following radioiodine damage and associated with external radiation

The late morphologic and functional changes in the thyroid gland after iodine-131 injury alone and in combination with external irradiation were studied. Different activities of the radionuclide were introduced in groups of experimental animals for 30 days, in the form of nuclear division products. External irradiation was applied with a single dose of 300 r. The kinetics of the radioisotope in the gland showed a decrease in the iodine-fixing function, under the influence of the radiation factor. In the later terms the impairement in the functional activity of the thyroid gland was demonstrated by changes in the gas exchange level, the changes being more pronounced after combined external and internal radiation treatment. The morphologic investigations showed increased hazard of development of tumors after irradiation of the gland with 1000 rad from incorporated iodine-131 and 300 rad external irradiation. Malignant neoplasms may equally develop after isolated external treatment with the afore-mentioned radionuclide doses. (author)