SURG-49. Gammatile Brachytherapy Safety and Efficacy in Recurrent Glioblastoma Patients: Outcomes from a Multi-Institutional Collaborative

Abstract INTRODUCTION Local control remains a major challenge in the surgical management of recurrent glioblastomas. Brachytherapy, such as Gammatile, offers a promising solution by delivering targeted radiation to the surgical bed. Here, we report the outcome of 60 consecutive recurrent glioblastoma patients who underwent resection/GT-implant. METHODS Clinical information was collected for consecutive, recurrent glioblastoma (isocitrate dehydrogenase wild-type) patients treated at the University of Minnesota, Honor Health, Robert Wood Johnson, Emory, Allegheny Health, East Carolina University, and Inova. Median progression-free and overall survival (mPFS and mOS) were calculated from the time of GT implant and stratified by methyl-guanine-methyl transferase (MGMT) status. RESULTS The study cohort comprised 47 male and 13 female subjects, with 1-3 previous glioblastoma recurrences. Karnofsky Performance Score (KPS) decreased post-resection/GT implant in 24 patients (41.2%); all experienced functional recovery, but to variable extents. Surgical/GT morbidities (6%) included hemorrhage, wound infection, and radiation necrosis (each at 1/60 or 2%). The median hospital stay was 2 days (range: 1- 21 days). 16.7% of the cohort required 30-day readmission, comparable to the expected readmission rate for craniotomy alone. There was no instance of rapid early recurrence, defined as tumor regrowth in the first MRI following surgical resection. Actuarial local control at one year was 92% and 80% for MGMT-methylated and -unmethylated patients, respectively (p=0.17). MGMT-methylated patients showed improved OS (mOS=14.7 mo) compared to unmethylated patients (mOS=7.9 mo, p=0.01). These results compare favorably to historical survival for these patient cohorts. Patients who showed a KPS decline after resection/GT-implant showed reduced OS relative to those with stable/improved KPS (mOS of 388 and 218 days, respectively, p=0.03). The number of tumor recurrences or prior bevacizumab did not prognosticate survival. CONCLUSION This multi-institutional experience supports the safety and efficacy of GT brachytherapy and provides a basis for selecting patients who would most benefit from this treatment.