131 iodine treatment for thyroid cancer is mainly aimed at differentiated thyroid cancer with suspected cancer remaining after radical resection. Although the malignancy of thyroid cancer is not high, it is often not easily detected in the early stage. By the time it is diagnosed as thyroid cancer, local or distal metastasis has often occurred. In some cases, metastases are the first thing found in the medical records, rather than the primary tumor. Since thyroid cancer is not sensitive to chemotherapy, it is a consensus in the industry that chemotherapy should not be used for thyroid cancer. In case of local or distal metastases, radical resection may not be complete or may not be possible, so high-dose 131I therapy is the best treatment for thyroid cancer after removal of the thyroid gland. Although the rate of iodine uptake is low, it is still higher than other tissues in the body. Especially after elimination of thyroid gland (or clear nail), the iodine uptake of some lesions can be increased due to the elimination of thyroid tissue. Therefore, the treatment has a better targeting property. In fact, the high cure rate and low recurrence rate of nail cancer are very closely related to the advent of this technology. After oral administration, 131 iodine is absorbed by the intestine and travels with the bloodstream to all parts of the body. Therefore, 131 iodine enters all sites where there are metastases, and the metastases with vigorous proliferation are also particularly sensitive to radiation, which is enough to become the basic condition for 131 iodine treatment of metastases of thyroid cancer. This is the basic condition for the treatment of metastatic thyroid cancer. Foreign countries started to apply 131 iodine treatment for metastases of differentiated thyroid cancer in the 1940s, and in China, 131 iodine treatment for metastatic thyroid cancer started in the late 1950s and early 1960s, and now this treatment method has been gradually accepted by clinicians and patients. Indications (1) Differentiated thyroid cancer with metastases with iodine uptake: (2) Differentiated thyroid cancer with local residual lesions after surgery: (3) Differentiated thyroid cancer with lymph node infiltration under microscope or metastases at microscope level cannot be excluded: (4) Differentiated thyroid cancer with metastases not taking 131 iodine after high dose 131 iodine treatment after surgery, possibly because the lesions have been (5) Differentiated thyroid metastatic carcinoma, recurrence after 131 iodine therapy: (6) The patient is in good general condition, with no abnormal liver or kidney function and white blood cells not lower than 3000. Start time: Usually we recommend patients to start iodine 131 therapy in January after surgery. By doing so, it not only leaves enough time for the incision to heal, but also depletes the iodine in the body, so that the thyroid cancer cells are in a state of starvation for iodine. Special reminder …… to abstain from iodized salt between the time of surgery and the start of iodine 131 treatment!