At present, the internationally recognized gold standard for the treatment of differentiated thyroid cancer is “surgery + isotope iodine-131 therapy + TSH hormone suppression therapy”, and the main advantages of iodine-131 therapy for differentiated thyroid cancer after surgery are as follows -131 can target the residual thyroid (cancer) tissues after surgery, and the rays released by it can produce ionizing radiation biology effect on postoperative hidden cancer foci and metastases, thus killing these functional tissues and reducing the risk of tumor recurrence and metastasis by 95%. 2.Iodine-131 whole body scan using SPECT/CT 3-7 days after treatment helps to search for metastases throughout the body, especially CT helps to clarify the anatomical location of the lesions, the size of the lesions and their relationship with surrounding organs, which is beneficial to the disease staging and prognosis assessment. 3. After iodine-131 treatment, the normal source of serum thyroglobulin (Tg) in the body is gradually depleted as the residual thyroid tissue is destroyed. Tg measurement (and iodine-131 whole-body scan) is usually performed after 3-6 months to monitor the recurrence or metastasis of thyroid cancer, which is extremely sensitive and specific for disease assessment. 4. After iodine-131 treatment, it is beneficial to improve the uptake of iodine-131 by metastases (commonly metastases in cervical lymph nodes, lung and bone) and enhance the biological effect of ionizing radiation, thus ultimately improving the efficacy of iodine-131 treatment for metastases of thyroid cancer.