Some parents ask in the clinic if they want to have I131 therapy after surgery. It is true that a significant number of children with thyroid cancer need this adjuvant treatment after surgery. This treatment has two main purposes: on one hand, it is to remove potential or hidden local cancer foci and metastases. For thyroid cancer with residual locally advanced tumors or metastases, I131 isotope therapy can destroy the residual intraoperative lesions or metastases, especially for distant metastases, I131 isotope therapy plays a very important role; on the other hand, I131 therapy can remove On the other hand, I131 treatment can remove residual thyroid tissue from the body so that the doctor can know whether there is recurrence and metastasis of thyroid cancer based on the HTg level in the blood. To some extent, I131 is equivalent to chemotherapy. However, I131 has fewer side effects and does not cause significant damage to major organs of the body, no bone marrow suppression, no significant gastrointestinal reactions, and generally no decrease in white blood cells or discomfort such as hair loss or vomiting. The main side effect of I131 treatment is damage to parotid tissue. A small number of patients have dry mouth after treatment. Some patients may also experience neck swelling and pain after initial I131 treatment. This is mainly due to the inflammatory response of the residual thyroid tissue during treatment, which mostly resolves with symptomatic treatment. Although some scholars believe that I131 treatment has the risk of secondary tumors, most studies have shown that postoperative I131 treatment for thyroid cancer in children has not resulted in secondary malignancies such as leukemia, so it is generally considered that reasonable I131 treatment is safe and effective. Generally, I131 therapy is required for tumor diameter R1.5 cm; tumor diameter less than 1.5 cm but multifocal; tumor involving thyroid envelope or extra-glandular organs; lymph node metastasis; and distant metastasis. The dose and frequency of I131 treatment will depend on the patient’s specific condition and sensitivity to I131. Children with thyroid cancer with lymph node metastasis in the neck but no distant metastasis will require I131 treatment about three times after surgery. Overall, thyroid cancer that is sensitive to I131 has better treatment results, but this method is not a substitute for surgery! Even for a tumor about 2cm in size, relying only on I131 treatment, at least 6 times more treatments are needed. Therefore, for thyroid cancer, if you can remove it surgically, you should try to remove it cleanly. When children are ready to receive I131 treatment after thyroid cancer surgery, they should stop eating seafood and other seafood for one month before treatment, stop taking thyroxine tablets and avoid eating iodized salt in their diet; after I131 treatment, they should supplement thyroxine tablets as soon as possible, review thyroid function regularly and adjust the dose of thyroxine tablets according to TSH, T3 and T4 levels in blood. When thyroxine tablets are first started, thyroid function should be retested in 1-2 months, and after thyroid function is adjusted to a satisfactory level, it can be retested once every six months. It is also necessary to avoid overexertion in daily life.