RADT-74. SURGICALLY TARGETED RADIATION THERAPY FOR RECURRENT GRADE IV GLIOMAS: INITIAL RESULTS FROM A MULTICENTER PROSPECTIVE COHORT STUDY

Abstract BACKGROUND Recurrent Grade IV gliomas are difficult to treat, particularly in patients who have already received definitive radiotherapy. Surgically targeted radiation therapy (STaRT) using Cesium-131 (Cs-131) collagen-tile brain brachytherapy (GammaTile®, GT Medical Technologies, Tempe, Arizona, USA), delivers immediate, localized radiation to the surgical cavity at higher doses than conventional adjuvant therapies, potentially improving clinical outcomes. METHODS The prospective observational registry (NCT04427384) is a multicenter study that evaluates clinical outcomes that measures effectiveness and safety of patients receiving brain tumor resection and STaRT. Herein, prospectively collected data from 122 patients with recurrent Grade IV glioma treated at 27 USA institutions were analyzed. Baseline demographic, clinical, and operative data were collected, including isocitrate dehydrogenase (IDH) mutation, O6-methylguanin-DNA methyltransferase (MGMT) promoter methylation status, extent of resection, and treatment-related toxicity. Patients were followed longitudinally to assess survival, recurrence, and toxicity. Kaplan-Meier curves and Cox regression were used for survival analysis. RESULTS The cohort included 71 males and 51 females (median age 61) and preoperative Karnofsky Performance Scale (KPS) of 80, but recovered by one month. Most patients (91.8%) had prior radiotherapy (median dose 60 Gy). Gross total resection was achieved in 66.7% of cases. A 12.2% toxicity rate occurred within 30 days; one patient experienced Grade 4 toxicity, there were no Grade 5 events. Median follow-up was 7.5 months, with overall median survival from STaRT of 13.6 months. IDH-mutant patients had longer survival than IDH wild-type (18.9 versus 13.1 months; p=0.045). MGMT methylation status was not associated with survival differences. Six- and 12-month progression-free survival rates were 74.6% and 56.6%, with local control (LC) at 91.8% and 87.7%, respectively. CONCLUSIONS STaRT was well-tolerated, demonstrating promising survival and LC outcomes, with median survival from STaRT exceeding published operative series. These results support further investigation of STaRT as part of a multimodal strategy for recurrent glioblastoma.