Clinical Outcomes in Patients with Recurrent Glioblastoma Treated with Proton Beam Therapy Reirradiation: Analysis of the Multi-Institutional Proton Collaborative Group Registry

Background As a means of limiting normal tissue toxicity, proton beam therapy (PBT) is an emerging radiation modality for glioblastoma (GBM) reirradiation. However, data for recurrent GBM treated with PBT-reirradiation is limited. Therefore, we analyzed treatment patterns, toxicities, and clinical outcomes of recurrent GBM patients treated with PBT-reirradiation using the multi-institutional proton collaborative group (PCG) registry. Materials/Methods Prospectively collected data for patients with recurrent GBM who underwent PBT while enrolled on PCG 01-009 (NCT01255748) were analyzed. We evaluated overall survival (OS), progression free survival (PFS) and toxicity. Toxicities were scored according to CTCAE v4.0. Descriptive statistics were used to report patient, tumor, and treatment characteristics. Multivariable analyses (MVA) for toxicity was conducted using logistic regression. The Kaplan-Meier method was used to calculate OS and PFS. MVA for OS and PFS was conducted using cox-proportional hazards models. SAS statistical software was used for analysis. Results We identified 45 recurrent GBM patients who underwent PBT-reirradiation between 2012 and 2018. Median time between initial GBM diagnosis and recurrence was 20.2 months. Median follow up time from PBT-reirradiation was 10.7 months. Median PFS was 13.9 months (95%CI: 8.23-20.0) and median OS was 14.2 months (95%CI: 9.6-16.9) after PBT-reirradiation. One patient experienced an acute grade 3 toxicity, four experienced late grade 3 toxicity (no ≥4 grade toxicities). MVA revealed that prior surgery was associated with a 91.3% decreased hazard of death (HR=0.087, 95%CI=0.02-0.42, p Conclusion This is the largest series to date reporting outcomes for PBT-reirradiation of recurrent GBM patients. Our analysis indicates that PBT is well tolerated and offers efficacy rates comparable to previously reported photon-reirradiation.