Thyroid cancer often occurs with multiple lesions at the same time. Even the most skilled surgeons can only remove the thyroid gland and cancerous tissues visually, and there may still be microscopic lesions left after surgery, and these residual thyroid cells and cancer cells (nail bed sites and metastases) can be eliminated by iodine-131. Furthermore, thyroid cancer grows slower than other malignant tumors. Within 3 to 5 years, it is difficult to determine whether the cancer has recurred or metastasized by ultrasound or CT alone without ECT iodine-131 whole body scan or blood sampling for thyroglobulin assay, but the patient may already have smaller cancer lesions in her body. In clinical practice, it is often found that patients with thyroid cancer who have not taken iodine-131 have a whole body scan after taking small doses of iodine-131 orally 3 to 5 years after surgery, and it is often found that metastatic or recurrent foci have appeared in the lymph nodes of the patient’s neck or in the thyroid bed area, while the TG level in the patient’s body is elevated, and most of the foci can be eliminated after high-dose iodine-131 treatment. Adverse effects of iodine-131 treatment Iodine-131 treatment is completed by drinking a small amount of iodine and swallowing it with a mouthwash, which is as easy as taking a sip of water without any discomfort. There are no major side effects like chemotherapy or radiotherapy. After taking a large dose of iodine-131 orally, there are usually only mild systemic reactions for a short period of time (about 1 week), including mild gastrointestinal reactions, swelling of the neck and parotid glands, weakness, loss of appetite, nausea, and dry mouth. Most of these reactions will resolve on their own, and some patients with severe reactions will also resolve after symptomatic treatment, with no effect on the patient’s daily life and work. Bone marrow suppression is extremely rare, and a few patients may have a transient decrease in peripheral blood count, while most of them may return to normal spontaneously. Iodine-131 treatment principle Iodine 131 has an effective half-life of 3.5-4.5 days in the thyroid tissue, releasing beta rays (99%) and gamma rays (1%). beta rays have a relatively short effective exposure distance of about 1 cm and are basically concentrated in the thyroid gland after administration, so they generally have no significant effect on surrounding organs and tissues and other people. After a few hours of concentrated exposure of the thyroid gland to beta radiation for a longer period of time, swelling of the thyroid gland occurs, vacuoles appear in the follicular cells and the nucleus is abnormal, and death occurs after a few days. Review of thyroid cancer after iodine-131 Because there is a possibility of recurrence or metastasis after thyroid cancer surgery, even for patients who are cured after taking iodine-131 ECT scan, they should be reviewed once every six months to one year, and if there is no problem in the review, they should be reviewed again in the second year, and if it is confirmed to be normal again, they can be reviewed every five years afterwards. The review items are thyroid ultrasound, ECT iodine-131 whole body scan, blood thyroglobulin level and thyroid function, especially the iodine-131 scan and TGA measurement are the main items to decide the patient’s further treatment plan. Iodine-131 therapy and pregnancy Most scholars believe that the incidence of leukemia in patients with DTC treated with iodine-131 is similar to the incidence in the natural population. However, high-dose iodine-131 therapy should not be given frequently. casara et al. studied l064 women of childbearing age treated with iodine-131 for DTC. Of these, 111 had one or more pregnancies after treatment, and 134 babies were born, none of which were found to be significantly abnormal. Sarkar et al. followed 40 patients with DTC who received an average of 17.4 GBq (200 mCi) of iodine-131 for 6 to 20 years and found no difference in the incidence of infertility, miscarriage, preterm delivery, or genetic defects from the general population. Schlumberger et al. observed 2133 pregnancies in 1877 female DTC patients of childbearing age and analyzed the effect of radioiodine treatment on pregnancy, receiving iodine-131 doses of 1.1 to 3.7 GBq (30 mCi to 100 mCi), and found that there was a high rate of miscarriage in pregnancies within 1 year after treatment, but the preterm, stillbirth, low birth weight or congenital anomalies The incidence of preterm delivery, stillbirth, low birth weight or congenital anomalies did not differ from normal subjects. Whether the increased rate of miscarriage within 1 year is due to abnormal thyroid function or is related to iodine-131 treatment needs to be further investigated, therefore, pregnancy should be required 1 year after high-dose iodine-131 treatment. Stop thyroid hormone replacement therapy; avoid iodine-rich foods (such as kelp, nori, sea fish, sea cucumber, shark fin, abalone, etc.); take non-iodized salt; avoid enhanced CT within 2 months before treatment.