3566 - Advancing the Value of Stereotactic Body Radiation Therapy (SBRT) in Unresectable and RAI Refractory Thyroid Cancer: A Locoregional Treatment

Purpose/Objective(s):

Utility of SBRT in management of unresectable or recurrent RAI refractory thyroid cancer involving the thyroid bed and regional neck.

SBRT is well established as an efficacious intervention for metastasis directed therapy, but currently the NCCN guidelines do not list SBRT for the management for unresectable thyroid cancer. In our cohort this was employed as a late salvage after multiple initial therapies failed for disease control and to delay initiation of or change in systemic therapy. Though thyroid cancer is not exactly rare in the general population, this cohort represents a small subset of presenting patients. Even still we present 27 patients with 28 lesions who underwent SBRT to the thyroid bed and regional neck for unresectable, RAI refractory or recurrent thyroid cancer.

Materials/Methods:

Under institutional IRB approval a retrospective cohort study was performed. Our local radiation oncology information system (ROIS) was queried for ICD-10-CM diagnosis code C73(malignant neoplasm of thyroid gland). Patients who received SBRT (=5Gy per fraction) to thyroid bed and/or neck were identified and relevant data points were extracted from the EMR. Survival analysis was accomplished via Kaplan-Meier estimation

Results:

ROIS query identified 413 unique treatments delivered to 181 patients, 27 of which received SBRT to 28 lesions of the thyroid bed and neck between 2019 and 2025. 14 female and 13 male patients with an average age of 69 at time of treatment harbored 20 papillary carcinomas, 3 anaplastic carcinomas, 2 Hurthle cell carcinomas, 1 follicular carcinoma, 1 medullary carcinoma and 1 differentiated high-grade thyroid carcinoma. Average number of prior therapies was 3 (range 0-7). 19 patients had undergone one or more RAI treatment, 2 had prior conventionally fractionated external beam radiation to 66Gy and 3 underwent definitive SBRT. The median dose delivered was 35Gy (range 25-40Gy) in 5fx. 10 lesions experienced infield failure with median time to failure of 38.7mo. Median follow up was 20.46mo (range 1-75mo) with a median overall survival of 61.3mo for the observation period. Three patients were lost to follow up and 6 died during the observation period. Of the 6 that died, 5 were secondary to progressive systemic disease and 1 due to unrelated hemorrhagic stroke. Of the 27pts there was one reported G3 toxicity of dysphagia.

Conclusion:

The use of SBRT in unresectable or recurrent RAI resistant thyroid cancer is an effective modality for the management of these complex patients with acceptable toxicity and durable local control. Application of SBRT to this treatment paradigm provides a valuable tool to arrest disease progression and alleviate systemic therapy burden. Recognition of SBRT as an efficacious late-stage treatment option for these difficult patients provides a valuable addition to the radiotherapy armamentarium.