Abstract
Differentiated thyroid cancer (DTC) generally carries an excellent prognosis, with surgery and radioactive iodine (RAI) forming the cornerstone of management. However, a subset of patients develops loco-regional advanced, recurrent, or RAI-refractory disease requiring additional local treatment modalities. External beam radiotherapy (EBRT) has historically played a limited role in DTC because of concerns regarding toxicity and lack of definitive survival benefit. Nevertheless, advances in radiation delivery techniques and improved understanding of disease biology have refined its role in carefully chosen high-risk patients. Comparison of the 2015 and 2025 American Thyroid Association (ATA) guidelines demonstrates that although there has been no major expansion in indications for EBRT, recent recommendations emphasize a more individualized and response-adapted approach. Modern techniques such as intensity-modulated radiation therapy (IMRT) and stereotactic body radiotherapy (SBRT) are increasingly incorporated into treatment strategies for unresectable disease, gross residual tumor, extranodal extension, soft tissue invasion, isolated unresectable nodal recurrence, and isolated RAI-refractory metastasis. Evidence suggests that EBRT may improve loco-regional control in selected patients, although overall survival benefit remains unproven. Concurrent chemoradiotherapy may further enhance local control in advanced disease but at the expense of increased toxicity. Additionally, for persistent loco-regional disease, repeated RAI therapy appears to provide limited benefit, further supporting selective use of EBRT in carefully chosen cases. This review summarizes the evolving role of radiation therapy in DTC and highlights the differences between the 2015 and 2025 ATA guidelines.

Key words: differentiated thyroid cancer, external beam radiotherapy, IMRT, SBRT, ATA guidelines, radioactive iodine, loco regional recurrence