PTC accounts for more than 90% of DTCs. The first treatment for DTC is surgery, and the extent of surgery depends on the patient’s risk level. Patients with stage II or higher risk should be treated with 131 iodine after subtotal thyroidectomy. Postoperative thyroid bed with residual thyroid tissue visualization should be treated with 131I to remove the residual thyroid tissue if the following conditions are met: 1. Patients with metastatic DTC. 2. Patients whose tumor has grown outward beyond the scope of thyroid tissue, regardless of the size of the primary focus. 3.Patients whose primary tumor is larger than 4cm even without any other risk factors. 4.Patients with primary tumor of 1-4 cm, not breaking through the thyroid envelope, with lymph node metastasis, or other high-risk factors (such as incomplete excision of primary foci, mismatch between thyroglobulin level and postoperative imaging results, etc.), or patients who belong to moderate to high risk by combining age, tumor size, lymph node status and histological pattern of tumor. 5. Patients with a single tumor lesion less than 1 cm, or patients with multiple tumors all lesions less than 1 cm, without any other high-risk factors, are not recommended for 131I removal therapy.