**Abstract**

Differentiated thyroid cancer is treated by surgery, radioiodine treatment, and Thyroid Stimulating Hormone (TSH) suppression. The role of external beam radiotherapy is mainly palliation of radio-iodine non avid metastatic lesions and in inoperable tumors. Metastasis involving weight-bearing bones and vertebral metastasis with impending spinal cord compression are primarily treated by external radiation. External Beam Radiotherapy improves loco-regional control in patients with gross residual disease after surgical resection. Patients with extra-thyroidal disease and positive margins are treated by adjuvant external beam radiotherapy, especially when the post op radio-iodine scan is negative. External beam radiotherapy is the treatment of choice for radio-iodine non avid inoperable loco-regional recurrence. SRS alone or surgery followed by SRS is the preferred treatment for solitary brain metastasis. Whole brain radiotherapy is the treatment of choice for multiple brain metastatic disease.

**Keywords:** differentiated thyroid cancer, external beam radiotherapy, iodine refractory disease, thyroid stimulating hormone (TSH), metastatic disease

### **1. Introduction**

Differentiated thyroid cancer (DTC) is treated by surgery, thyroid stimulating hormone (TSH) suppression, and radioiodine therapy according to the risk stratification [1, 2]. External Beam Radiotherapy (EBRT) is used in selected patients in the adjuvant setting. EBRT is mainly used in the palliation of radio-iodine non-avid metastatic disease and inoperable tumors. There are no prospective randomized trials on EBRT in DTC. The available evidence is from single institution retrospective studies, systematic reviews, and meta-analysis. In this chapter, we discuss the role of EBRT in localized and metastatic DTC. **Figure 1** summarizes the role of EBRT in differentiated thyroid cancer.

**Figure 1.** *The role of EBRT in differentiated thyroid cancer.*
