Pulsed Reduced Dose Rate Re-Irradiation for Patients with Recurrent Grade 2 Gliomas

Patients with grade 2 glioma exhibit highly variable survival. Re-irradiation for recurrent disease has limited mature clinical data. We report treatment results of pulsed reduced dose rate (PRDR) radiation for patients with recurrent grade 2 glioma. A retrospective analysis of 58 patients treated with PRDR from 2000-2021 was performed. Radiation was delivered in 0.2 Gy pulses every three minutes encompassing tumor plus margin. Survival outcomes and prognostic factors on outcome were Kaplan Meier and Cox regression analyses. The median survival from date of initial surgery was 8.6 years (95% CI 5.5-11.8 yrs). 69% of patients showed malignant transformation to grade 3 (38%) or grade 4 (31%) glioma. Overall survival following PRDR was 12.6 months (95% CI 8.3-17.0 mo) and progression free survival was 6.2 months (95% CI 3.8-8.6 mo). Overall response rate based on post PRDR MRI was 36%. In patients who maintained grade 2 histology at recurrence, overall survival from PRDR was 22.0 months with five patients remaining disease free, the longest at 8.2 and 11.4 years. PRDR was generally well tolerated. To our knowledge, this is the largest reported series of patients with recurrent grade 2 gliomas treated with PRDR radiation for disease recurrence. We demonstrate promising survival and acceptable toxicity profiles following re-irradiation. In the cohort of patients who maintain grade 2 disease, prolonged survival (>5 years) is observed in selected patients. For the entire cohort, 1p19q co-deletion, KPS, and longer time from initial diagnosis to PRDR were associated with improved survival.