External Radiotherapy for Locoregional Control in Thyroid Carcinoma

Most patients with well-differentiated thyroid cancers (WDTC) are adequately treated with surgery, radioactive iodine, and TSH suppression by thyroxine. External radiotherapy (ERT) is reserved for selected cases and for older patients. Some of the indications for ERT to neck include adjuvant treatment for gross or microscopic disease after surgery, palliation of locally advanced unresectable tumor, or as salvage for recurrent disease which is not amenable to surgery or does not uptake radioactive iodine. High radiation dose of at least 60Gy is required for locoregional control of gross or microscopic residual disease. As even patients with recurrent or metastatic disease can have long survival, it is important to minimize late radiation-induced morbidity without compromising local control. Modern ERT technique like intensity-modulated radiotherapy allows high radiation dose to be delivered to the large, complex target volume while protecting the adjacent critical normal structures like the trachea, larynx, esophagus, and cervical spinal cord.