Iodine-131 nail clearing for highly differentiated thyroid cancer (papillary and follicular carcinoma) is also called “internal radiotherapy”. Surgery for thyroid cancer can only remove the thyroid gland or cancerous tissues visually, but not completely under the microscope, i.e. a small amount of thyroid cells or possible cancer cells remain after surgery. Moreover, iodine-131 nail cleansing also provides convenience for future follow-up and treatment. Indications and contraindications of iodine-131 nail scavenging For postoperative patients, the size of the lesion, external invasion, lymph node metastasis, distant metastasis and patient’s will should be determined based on pathological results combined with comprehensive clinical assessment. According to the CNNC guidelines for thyroid cancer, iodine-131 treatment may not be recommended for patients with differentiated thyroid cancer with foci less than 1 cm in diameter, foci confined to the thyroid gland or without extra-thyroid invasion, no vascular invasion (follicular carcinoma), and no lymph node or distant metastasis. However, if the thyroid gland has been completely resected, iodine-131 can be performed to clear the nail in order to facilitate future follow-up. Iodine-131 clearance is recommended for patients with one of the following conditions: lesions larger than 4 cm in diameter, obvious extrathyroidal invasion, known or suspected lymph node metastases or distant organ metastases, or extensive vascular invasion (follicular carcinoma). In addition to the above two conditions, those who meet one of the following conditions choose to recommend or review follow-up for further evaluation of iodine 131 nail scavenging: primary tumor 1-4 cm, primary tumor 2-4 cm (follicular carcinoma), extra-thyroidal microinvasion, multiple foci, abnormal postoperative TG, and age >45 years at diagnosis of thyroid cancer. However, iodine 131 nail clearance is still recommended if more than one of the above factors are present at the same time. Iodine-131 therapy is contraindicated during pregnancy, lactation, and planned short-term (within 1 year) pregnancy. Precautions for iodine-131 treatment Eugenol or thyroid tablets must be stopped for 4-6 weeks prior to iodine-131 treatment in order to elevate the TSH in the body to facilitate the uptake of iodine-131 by the lesion. A low iodine diet (avoiding seafood and iodine-rich foods and medications) for 4-6 weeks prior to Iodine-131 treatment is also required to increase the uptake of Iodine-131 by the lesion. Due to the high level of radioactivity in the patient’s body after oral Iodine-131 treatment, hospitalization is required for high dose Iodine 131 treatment. Family members are not allowed to accompany the patient during the inpatient isolation period.