RADT-89. MINIMALLY INVASIVE RESECTION WITH CS-131 BRACHYTHERAPY VS POSTOPERATIVE SRS FOR BRAIN METASTASES: LOCAL RECURRENCE OUTCOMES FROM A MATCHED COHORT

Abstract INTRODUCTION Metastatic brain tumors are often treated with resection followed by stereotactic radiosurgery (SRS), which carries risks of radiation necrosis and limited control of microscopic disease. Alternatively, minimally invasive keyhole craniotomy (MIKC) with intraoperative Cesium-131 brachytherapy (Cs-131BT) delivers immediate, cavity-directed radiation with minimal surrounding tissue exposure. A prospective study at Ochsner Medical Center (2019–2022) showed high local control and low toxicity with MIKC + Cs-131BT. We conducted a retrospective matched cohort study comparing recurrence and toxicity outcomes of MIKC + Cs-131BT to standard resection + SRS. METHODS Patients treated for brain metastases from 2019–2025 with resection followed by SRS were matched 1:1 to MIKC + Cs-131BT patients based on primary tumor type, age (±10 years), and tumor volume (±30%). Matching quality was evaluated using Wilcoxon signed-rank tests and Spearman correlation. Recurrence and radiation necrosis were compared using McNemar’s (matched pairs) and Fisher’s exact tests (overall incidence). Time-to-event outcomes were analyzed with Kaplan–Meier curves and log-rank testing. RESULTS 38 patients (19 matched pairs) were analyzed. Age and tumor volume were balanced between Cs-131BT and SRS groups (median 60 vs, 65 years, p = 0.68; 11 vs, 12 cm³, p = 0.47). Local recurrence occurred in 0 Cs-131BT and 2 SRS patients (p = 0.48), while distant recurrence occurred in 3 and 8 patients, respectively (p = 0.18). Radiation necrosis was seen in one patient in the SRS group. Overall recurrence rates were not significantly different by Fisher’s exact test. Time-to-distant recurrence favored Cs-131BT (HR = 0.49), though this did not reach statistical significance (p = 0.24). CONCLUSION This matched analysis found no statistically significant differences in recurrence or toxicity between MIKC + Cs-131BT and resection + SRS. However, favorable trends observed with Cs-131BT may reflect clinical benefits that the study was underpowered to detect. Larger prospective studies are warranted to validate these findings.