Not all patients with postoperative thyroid cancer can be treated with iodine isotope therapy. Papillary and follicular carcinomas have the iodine-absorbing function of normal thyroid cells, so metastases from these two types of cancer can be treated with iodine isotope therapy, while undifferentiated and medullary carcinoma cells do not have the iodine-absorbing function, so they cannot be treated with iodine isotope therapy. Not all patients with postoperative thyroid cancer need iodine isotope therapy. In November 2009, the American Thyroid Association (ATA) published in its official journal THYROID a revised version of its guidelines for the diagnosis and treatment of thyroid cancer, in which iodine-131 ablation should be recommended for patients with thyroid cancer who have any of the following conditions. The following are the circumstances: known distant metastases to lung, bone, etc. (M1); intraoperative visualization of the tumor breaking through the thyroid envelope and invading the subcutaneous soft tissue, larynx, trachea, esophagus, recurrent laryngeal nerve, prevertebral fascia, or encircling the carotid artery and mediastinal vessels (regardless of tumor size, T4); primary tumor more than 4 cm in diameter (T3); tumor not breaking through the thyroid envelope and between 1 -4 cm, but with proven lymph node metastasis or other intermediate or high risk of recurrence and death. These include: surgical pathology suggesting microscopic tumor invasion of the soft tissues surrounding the thyroid, highly invasive histological manifestations (e.g., hypercellular, columnar cell, insular cell, diffuse sclerosis, hypofractionated carcinoma, follicular carcinoma, eosinophilic carcinoma, etc.) or vascular invasion, incomplete tumor resection, and hypothyroglobulinemia.