After surgery and 131I treatment for invasive DTC, the role of external irradiation therapy in reducing the recurrence rate is unclear and is not recommended for routine use. External irradiation therapy may be considered in the following cases: (i) for local palliative treatment; (ii) with residual tumors visible to the naked eye that cannot be treated with surgery or 131I; (iii) painful bone metastases; and (iv) located in critical sites that cannot be treated with surgery or 131I (e.g., spinal metastases, central nervous system metastases, certain mediastinal or subserosal lymph node metastases, pelvic metastases, etc.). DTC is not sensitive to chemotherapeutic agents. Chemotherapy is only used as palliative treatment or as an attempted treatment after other means have failed. Doxorubicin (Adriamycin) is the only drug approved by the FDA for metastatic thyroid cancer, and its efficacy against lung metastases is superior to that of bone metastases or lymph node metastases.