Main Session
Sep 27
PQA 01 - Gastrointestinal Cancer and Central Nervous System

2138 - Hypofractionated Proton Reirradiation for Recurrent Glioblastoma: Clinical and Dosimetric Outcomes from a Large Single Institution Series

03:00pm - 04:00pm ET
Poster Hall - Exhibit Hall A
Screen: 10
POSTER

Presenter(s)

Lauren Linkowski, MD, BS Headshot
Lauren Linkowski, MD, BS - Hospital of the University of Pennsylvania, Philadelphia, PA

L. C. Linkowski1, I. Messing2, M. Berger2, C. Hollawell2, C. Friedes2, D. A. Alexander1, X. Wang3, A. Desai4, R. E. Phillips4, D. M. O'Rouke5, N. Amankulor6, C. Jackson6, H. G. Hubbeling2, G. Kurtz2, S. J. Bagley7, J. D. Bradley1, S. Mohan8, M. Alonso-Basanta1, and E. S. Lebow1; 1Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 2Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, 3Department of Biostatistics and Epidemiology, University of Pennsylvania, Philadelphia, PA, 4Division of Neuro-Oncology, University of Pennsylvania, Philadelphia, PA, 5Hospital of the University of Pennsylvania, Department of Neurosurgery, Philadelphia, PA, 6Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, 7University of Pennsylvania, Philadelphia, PA, 8Department of Radiology, University of Pennsylvania, Philadelphia, PA

Hypofractionated Proton Reirradiation for Recurrent Glioblastoma: Clinical and Dosimetric Outcomes from a Large Single Institution Series

 

Abstract

 

Purpose/Objective(s): Management of recurrent glioblastoma remains challenging, and no therapy has been proven to prolong survival. Reirradiation is often limited by cumulative dose to critical structures. We evaluated clinical outcomes, toxicity, and cumulative dosimetry associated with hypofractionated proton reirradiation among patients with recurrent glioblastoma.

 

Materials/Methods: We retrospectively identified patients with recurrent glioblastoma treated with hypofractionated reirradiation courses of 35 Gy in 10 fractions. Cumulative composite dosimetry was calculated using EQD2 (α/β = 2) for organs at risk (OARs). Overall survival (OS) was estimated using Kaplan Meier methods. Cox proportional hazards modeling was performed to identify factors associated with OS. A contemporaneous cohort treated with hypofractionated photon reirradiation was identified for comparison.

 

Results: A total of 89 patients were treated with hypofractionated proton reirradation for recurrent glioblastoma between 2015 and 2025 with median follow up of 7.2 months. Median age was 58 years (IQR 48–68), and 48% underwent reresection prior to reirradiation. Composite dosimetry demonstrated that the initial radiation course accounted for the majority of cumulative OAR dose, with proton reirradiation contributing limited additional exposure. Median OS from reirradiation in the proton cohort was 8.3 months (95% CI 6.27–9.47), with 6 and 12 month OS of 62.6% and 24.9%, respectively. On multivariable analysis, increasing age was independently associated with worse OS. A comparator cohort of 49 patients treated with photon reirradiation was identified. OS did not differ between proton and photon reirradiation cohorts. 8 (5.8%) patients experienced Grade 3 or 4 radiation necrosis. No Grade > 4 toxicities were observed.

 

Conclusion: To our knowledge, this study represents the largest reported experience of hypofractionated proton reirradiation for recurrent glioblastoma and is the first to integrate dosimetric evaluation and a photon comparator. Hypofractionated proton reirradiation was feasible and associated with favorable toxicity outcomes, supporting its use as a retreatment option. Prospective studies are needed to further define optimal patient selection.