RTHP-35. RE-IRRADIATION USING PULSED REDUCED DOSE RATE RADIATION THERAPY IN PATIENTS WITH GRADE 2 GLIOMAS

Abstract BACKGROUND The time course of progressive grade 2 glioma can span nearly a decade. However, much less is known about re-irradiation in this cohort than in high grade patients. Pulsed reduced dose rate (PRDR) radiation therapy is a method of radiation delivery, which may spare normal tissues by slowing the rate of radiation delivery to allow repair. METHODS We identified consecutive patients from an institutional database initially diagnosed with grade 2 glioma from 2001 to 2017 who underwent pulsed reduced dose rate radiation therapy. Radiation was delivered in 20 cGy pulses every three minutes, most commonly with a 3D conformal, three field technique, encompassing gross disease with a 1–2 cm margin. Kaplan Meier method was utilized to analyze patient outcomes. RESULTS 35 patients with grade 2 glioma were identified. The median survival from the date of the first surgery was 103 months (95% CI 78–129 mo). 71% underwent at least a second resection and 86% of patients receiving chemotherapy. 80% of patients underwent transformation to grade 3 (51%) or grade 4 (29%) glioma. Overall survival from PRDR was 9.8 months (95% CI 4.5–14.5mo) and progression free survival was 6.2 months (95% CI 5.1–7.4) in all patients. Overall response rate was 37%. In patients who remained grade 2 histology, overall survival was 13.3 months and two patients remain disease free at 83 and 34 months with overall response of 71%. Four seizures were documented, otherwise treatment was well tolerated. CONCLUSIONS Progressive grade 2 glioma can progress and evolve over nearly the course of a decade. This study demonstrates the efficacy of re-irradiation in prolonging survival in these patients by delaying progression. In patients who remain with grade 2 disease, prolonged salvage of their disease appears possible.