Clinical Outcomes After Proton Therapy Reirradiation for Recurrent Malignant Glioma: Analysis From the Prospective Proton Collaborative Group Registry.

PURPOSE

Optimal treatment for recurrent glioma after prior radiation therapy (RT) is not well established. Proton therapy (PT) is increasingly used for reirradiation (ReRT); however, treatment outcomes, toxicities, and prognostic factors for PT-ReRT remain poorly defined.

METHODS AND MATERIALS

The prospective, multi-institutional Proton Collaborative Group registry was queried for patients with malignant glioma who underwent PT-ReRT between July 2011 and December 2023; only patients with at least one follow-up encounter were included. Overall survival (OS) and progression-free survival were assessed using the Kaplan-Meier method, and Cox proportional hazards regression was used for uni- and multivariable analyses (univariable analysis and multivariable analysis).

RESULTS

The study cohort included 143 patients, the median follow-up was 11.2 months, and the median time interval (TI) from prior RT (median 58.5 Gy, IQR, 54-60 Gy) to PT-ReRT (median 44.6 Gy, IQR, 39.4-55.9 Gy) was 42.4 months. Median progression-free survival and OS were 8.1 and 11.2 months, respectively. On univariable analysis, improved OS was associated with oligodendroglioma and astrocytoma histology compared to glioblastoma, TI >60 months, Eastern Cooperative Oncology Group performance status 0, and ReRT dose ≥50 Gy. On multivariable analysis, improved OS remained associated only with oligodendroglioma and TI >60 months. Acute and late grade 3 toxicity occurred in 7% and 4%, respectively. Acute grade 3 toxicity was associated with poor performance status. Incidence of radiographic radiation necrosis was 19%.

CONCLUSIONS

In the largest series of glioma PT-ReRT reported to date, retreatment was well tolerated with variable outcomes based on clinical prognostic factors. Toxicity rates were similar compared to photon-based literature despite a high median ReRT prescription dose.