Proton re-irradiation of unresectable recurrent brain gliomas: clinical outcomes and toxicity

Purpose: To assess the efficacy and tolerance of proton reirradiation in patients with unresectable recurrence of previously irradiated brain gliomas. Methods: Between February 2016 and December 2019, 44 patients with in-field recurrence after prior irradiation of brain gliomas were irradiated with intensity-modulated proton therapy. Seven patients (15.9%) originally had low-grade (WHO grade I-II) gliomas, nine patients (20.4%) had anaplastic astrocytoma (WHO grade III), and 28 patients (63.7%) had glioblastoma (WHO grade IV). All tumors were unresectable due to their localization. After a median time from the prior irradiation of 28.0 months [range, 12 to 173], patients received PT with 2.0 and 3.0 GyRBE per fraction, with median proton EQD(2) (alpha/beta=10) to a tumor of 55.0 GyRBE [range, 46.0 to 61.75]. Adjuvant chemotherapy (Temozolomide, or Procarbazine, Lomustine and vincristine, or Bevacizumab with Irinotecan) received 86.9% of the patients (n=40). Treatment-related toxicity was reported following CTCAE. Results: The median survival time was 12 months, with 1-year and 2-years overall survival (OS) amounting to 49.6% and 35.1%, respectively. The median progression-free survival (PFS) was 9 months, with 1- and 2-years PFS of 30.5% and 10.2%, respectively. Twenty-six patients died by the time of analysis; among them were 5 non-cancer deaths (19.2%), and 4 patients (15.4%) died of chemotherapy-associated severe toxicity. The incidence rate of radiation-induced necrosis was 6.8% (3 events). Conclusions: Based on our results, we suggest re-irradiation of recurrent brain gliomas with proton therapy is able to achieve reasonable tumor control. Low adverse events rate and promising outcomes make it a safe treatment option with curative intent, even in unresectable cases.