Thyroid cancer is broadly divided into differentiated type and undifferentiated type, and papillary carcinoma is the differentiated type. Differentiated type has the function of iodine 131 uptake, so it is used clinically to treat differentiated thyroid cancer, especially bloodstream metastases (lung and bone). I. Indications 1. Patients with stage III and IV (TNM stage) differentiated thyroid cancer; 2. All patients younger than 45 years old with stage II differentiated thyroid cancer; 3. Most patients older than 45 years old with stage II differentiated thyroid cancer with tumor diameter greater than 2CM less than or equal to 4CM; 4. Patients with selective stage I differentiated thyroid cancer, in addition to those with multiple tumor lesions, lymph node metastasis, and Patients with extra-thyroidal or vascular infiltration (mostly stage III); 5. Patients with aggressive type of pathology (hypercellular, islet cell or column cell type). Contraindications Age less than 20 years is not recommended (under 30 years is not preferred); III degree hypoalbuminism; pregnant and lactating women; patients with severe cardiac, hepatic and renal insufficiency; patients with extreme enlargement of the thyroid gland with symptoms of compression; severe infiltrative proptosis; hyperthyroidism crisis.