30 Radiotherapy Approaches and Clinical Outcomes in Brain Metastases in Differentiated Thyroid Cancer

Brain Cancer Canada Travel Award Recipient BACKGROUND Brain metastases (BrM) from differentiated thyroid cancer (DTC) are rare. We analyzed the outcomes of patients with DTC BrM treated with radiotherapy (RT) at our institution. METHODS Patient characteristics and treatment details were retrospectively collected for patients treated January 2013-December 2023. RESULTS Among 37 patients, median age at BrM diagnosis was 64 years (range 33-87); 59% were male. Papillary histology was most common (89%); 42% of tumors with known molecular profile harbored BRAF V600E mutation. Lenvatinib was the commonest agent of the 79% of patients who received systemic therapy. Initial brain-directed approach was Gamma Knife stereotactic radiosurgery (SRS) in 21 patients (57%), whole-brain RT (WBRT) in 30%, and focal RT on a linear accelerator in 13% (3/5 postoperative). Median survival was 22 months (range 1–135) from BrM diagnosis: 22 months for SRS/focal RT and 8.9 months for WBRT. Median time to local/distant brain progression was 12 months (range 1-46), 6.5 months (range 1-31), and 27 months (range 18-31), for the entire cohort, SRS, and focal RT, respectively. Most (54%) WBRT patients lived <6 months; of 5 patients who lived >6 months, median time to any brain progression was 30 months (range 7-46). Local failure was seen in 7.7% of SRS/focal RT patients and 2/7 WBRT patients with >2 months of imaging follow-up. CONCLUSIONS Our study represents the largest cohort of DTC BrM treated with radiotherapy. SRS offers durable local control. While most patients treated with WBRT are at end-of-life, WBRT offers long-term survivors durable brain control.