Thyroid tumors requiring iodine 131 therapy: 1. distant metastases such as lung and bone; 2. tumors breaking through the true perithelium of the thyroid gland; 3. tumors not breaking through the perithelium but having lymph node metastases, poor pathological subtypes of papillary carcinoma (high cell, columnar cell, diffuse sclerosis, etc.), multiple carcinoma foci, vascular invasion, non-papillary carcinoma (follicular, hypofractionated); 4. postoperative assessment of high risk of recurrence and metastasis. Other conditions of high risk. For those who are older than 45 years old and whether the tumor diameter exceeds 2cm or 3cm, whether these cases must be treated with iodine 131 therapy needs to be combined with clinical risk assessment and cannot be considered as indications for iodine 131 therapy.