Definitive Radiotherapy for the Treatment of Gross Disease in Unresected Differentiated Thyroid Cancer.

While surgery (with or without radioactive iodine (RAI)) is the mainstay of locoregional control in differentiated thyroid cancer (DTC), patients with unresectable disease present a clinical challenge. Uncontrolled disease in the neck can lead to substantial morbidity and mortality in DTC and obtaining locoregional control is vital to preserving quality of life and longevity. High dose definitive radiotherapy (RT) for gross disease in DTC is understudied. This study examines the efficacy of definitive RT in this setting. From an IRB-approved registry of head and neck cancer cases treated at a tertiary care center over a period of 8 years (2014-2022), patients with incompletely resected or unresectable DTC including papillary, follicular, mixed, medullary, and poorly differentiated types were identified. All patients were treated to the neck and/or thyroid regions with visible gross disease to a definitive dose of radiation. The primary endpoint was local control within the radiated portal with a secondary endpoint of locoregional control within the neck. A total of 31 patients were identified, of whom 74.2% were Caucasian. Fourteen were female (45.2%), and 17 (54.8%) were male. The median age was 68 years (range 26-90) and the median follow-up was 31 months. Histologically, 19 (61.3%) cases were papillary, 4 (12.9%) were follicular, 2 (6.5%) were mixed, 3 (9.7%) were medullary, and 3 (9.7%) were poorly differentiated. Among patients with non-medullary DTC 18 (69.2%) received prior RAI. Twelve patients were treated with radiation at initial diagnosis, while 19 patients were treated at the time of recurrence; two patients received concurrent chemotherapy. Twenty-eight patients (90.3%) were treated with IMRT and 3 (9.7%) were treated with SBRT. The median dose to the gross disease was 66 Gy (range 30-70.4) in 32 fractions (range 5-35). Overall, 5 patients (16.1%) experienced a locoregional failure after RT and all experienced failure in the RT portal. The actuarial infield control/locoregional control of radiation therapy at 3 and 5 years was 84.8% and 74.2%, respectively. Overall survival at 3 and 5 years was 68.5% and 47.4%, respectively. Among patients who had a locoregional failure after RT, 2 patients were salvaged with systemic therapy, 2 patients with surgery, and 1 patient with SBRT re-irradiation (40 Gy/5 fractions). The patient salvaged with SBRT remains without disease 8 months post-RT. Definitive radiotherapy is a highly effective strategy to obtain durable control of unresected DTC. It should be standard for unresected disease and considered as a viable alternative for patients with borderline resectable disease for whom resection would be highly morbid. [ABSTRACT FROM AUTHOR]