1. What is radioactive iodine (isotope) therapy and how is radioactive iodine therapy a treatment method. 1) Internal use therapy of radioactive iodine is: one of the isotopes of radioactive iodine called 131-iodine is taken in (liquid) capsules containing this isotope to treat thyroid disease. (2) Internal application therapy of radioactive iodine is: Treatment of thyroid disease by taking advantage of the property that thyroid cells can take up more than 60% of the radioactive iodine that enters the body. 3) The radioactive iodine gathered in the thyroid gland emits rays that slowly destroy the cells that produce thyroid hormones. 4) The treatment of GD is that the cells that produce thyroid hormone become less and the thyroid function normalizes. (5) The treatment of thyroid cancer is: to destroy cancer cells and metastases. 2) Nature of radioactive iodine: Iodine exists in large quantities in many known seafood products such as kelp, and is gathered in the body by the thyroid gland to become a raw material for synthesizing thyroid hormones. The 131-iodine used in radioactive iodine internal therapy has the same properties as the iodine contained in food, which is aggregated by the thyroid gland in the body and produces beta rays that destroy thyroid cells. The beta rays emitted by radioactive iodine have a range of (1 to 2 mm), and the organs adjacent to the thyroid gland cannot be damaged by them. Moreover, the treatment dosage is so small that it is metabolized in the body in a very short period of time and the body is not damaged. 3. History and safety: Internal radioactive iodine therapy was first introduced in 1941, when it was administered in the United States. Since then, more and more people have been receiving this treatment method, and there have been no current reports of leukemia and thyroid cancer caused by the treatment dosage of radioactive iodine. Nowadays, 80% to 90% of GD patients in the United States are treated with radioactive iodine. In Japan, the number of patients treated with this method has been increasing since 1998, and the number of patients in specialized medical institutions is enough for outpatient clinics.