In fact, although the occurrence and progression of most thyroid cancers are slower than other tumors, it does not mean that surgical removal of the primary lesion can solve all the problems, and subsequent 131 iodine treatment is not only necessary, but also necessary as early as possible. Cancer cells are good at “lurking” A characteristic of thyroid cancer is that it is good at “lurking”. It has a long progression cycle in the thyroid tissue and is mostly bilateral, microscopic and multifocal, and is prone to local organ invasion and local lymph node metastasis. Therefore, it is necessary to perform 131 iodine to remove the residual thyroid gland after surgery. If distant metastases (such as lung metastases or bone metastases) or lymph node metastases that cannot be removed by surgery are found at the time of surgery, it is necessary to remove the metastatic lesions as soon as possible. In addition, after 131 iodine treatment, it is more beneficial to monitor thyroid cancer by whole body 131 iodine imaging and measuring serum thyroglobulin level. Studies have shown that the recurrence rate of thyroid cancer after surgical resection alone is three to five times higher than the recurrence rate of surgical resection plus postoperative radioactive 131 iodine clearance. 131 iodine clearance of residual thyroid tissue after thyroid cancer surgery can significantly reduce the chance of tumor recurrence and metastasis, as well as decrease the death rate. 131 iodine treatment is not as scary as imagined. Many patients are willing to receive 131 iodine treatment in order to eradicate the lesion, but they are hesitant to accept the legendary “atomic bomb” of radiation, whether it will destroy cancer cells as well as healthy cells in the body. Can their bodies withstand this seemingly powerful treatment, and what are the side effects of 131 iodine treatment? Will the treatment endanger family members? Will the patient’s reproductive function be affected after treatment? Although 131 iodine is a radioactive drug, the side effects of this treatment are far less than those of radiotherapy and chemotherapy, and do not cause serious side effects such as vomiting, hair loss, or hematuria. Studies have shown that 131 iodine itself releases a small amount of gamma rays, and because of its small amount of radiation, it has no adverse effects on the patient’s future marriage or fertility, and does not enhance the probability of tumors in other areas. During treatment, patients generally have only mild gastrointestinal reactions, swelling of the neck and swelling of the parotid glands, most of which will resolve on their own. Since many foods and medications can affect the effect of 131 iodine treatment, it is necessary to stop thyroid hormone replacement therapy during the preparation phase before hospitalization. 2. CT (because the contrast agent will affect the 131 iodine treatment) If the patient is confirmed to have thyroid cancer after surgery, he/she should visit nuclear medicine to have his/her condition evaluated by a professional nuclear medicine physician and decide whether the patient needs 131 iodine treatment. Do not be paralyzed by the disease and delay the best time for treatment.