P09.05.b Particle Re-Irradiation for the Treatment of Recurrent Intracranial Meningiomas

BACKGROUND Recurrent intracranial meningiomas have no unique treatment. Particle re-irradiation (reRT) is one of the therapeutic options available and the present study aims at investigating its oncological outcomes. MATERIAL AND METHODS A retrospective analysis was conducted on patients with recurrent intracranial meningiomas treated with both proton and carbon ion reRT from 2016 to 2024. Local control (LC) and overall survival (OS) were evaluated with the Kaplan-Meier method. For prognostic factors analysis the Log-Rank test for testing curve equality was performed and p-value was reported. Toxicity was registered according to Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. RESULTS 20 patients were included, with 11 patients receiving carbon ion reRT and 9 patients receiving proton reRT. With a median follow-up of 22.8 months (range, 4.2-96.2), 5 patients experienced a local relapse after particle reRT. The 1- and 2-year LC was 88.2%, while 5-year LC was 52.3%. A statistically significant difference in terms of median LC was found between grade I and grade II/III meningiomas (40.6 vs 28.4 months, p = 0.0035). OS at 1 and 2 years were respectively 89.5% and 83.1%. There were no grade 3 or higher acute and late toxicities. Four patients developed radiation-induced brain necrosis (RBN), two patients an asymptomatic grade 1 RBN and two patients a grade 2 RBN positively treated with dexamethasone. CONCLUSION Particle reRT is a safe and promising option for recurrent intracranial meningiomas. Multidisciplinary approach is highly recommended.