Currently, the optimal treatment for thyroid cancer is internationally recognized as consisting of three parts: 1. Surgical removal of the primary and resectable metastases. 2.Destruction of residual thyroid tissue and occult metastases after surgery with radioactive 131 iodine. 3. Lifelong thyroid hormone suppression therapy to correct hypothyroidism and inhibit the recurrence and growth of tumor. Many people think that once thyroid cancer surgery is done, especially when the body condition feels good, everything is fine. According to foreign data, the recurrence rate is as high as 32.0% for surgery alone, 11.0% for surgery + oral thyroid hormone, and 2.7% for surgery + 131 iodine therapy + oral thyroid hormone. The mortality rate of surgery alone is 3.8 to 5.2 times higher than that of surgery + 131 iodine treatment, and the recurrence rate is 4 times higher than that of surgery + 131 iodine treatment. Therefore, for patients with thyroid cancer, regardless of whether they have conscious symptoms after surgery, 131 iodine should be routinely applied to remove residual thyroid tissue for long-term benefits; if metastasis occurs, 131 iodine should also be applied to destroy the metastatic foci. 131 iodine treatment for thyroid cancer is a biological missile type of treatment, in which the drug only reaches the diseased tissues and has less impact on other organs and tissues throughout the body, so it is a treatment method with few side effects and complications. Generally, in the first few days after taking the drug, there may be loss of appetite, poor mental health, swelling and pain in the neck, etc. Most of them are not serious and do not require special treatment, and will disappear on their own after a few days.