131 Clearance therapy is indicated for DTC metastases (including local lymph node metastases and distant metastases) that cannot be surgically removed but have iodine uptake. The aim of treatment is to remove the lesion or to provide partial palliation of the disease. The efficacy of clearance therapy is directly related to the degree of 131 uptake by the metastases and the retention time of 131I in the lesions, and is also influenced by the patient’s age, the size and location of the metastases, and the radiosensitivity of the lesions to 131. Younger patients have a greater likelihood of obtaining a cure, and small metastases in soft tissues and lungs are easily cleared; metastases that have formed substantial masses or bone metastases with combined bone destruction are often poorly treated with focal clearance, even if the lesion is clearly ingested with 131. Advanced age, concomitant other serious diseases or intolerant of pre-treatment hypothyroidism should not be treated with 131 focal clearance. Metastases located at critical sites (e.g. intracranial or paraspinal, intra-airway, paragonadal metastases, etc.) are not suitable for 131 focal clearance therapy if they are inoperable, even if the lesions take up 131 significantly, and should be treated by other methods.