Three-year insights from a proton therapy centre: Evolving strategies in ependymoma treatment planning.

Background: Treatment of posterior fossa ependymoma with proton therapy (PT) is challenging due to the proximity to the brainstem and potential risk of brainstem toxicity. Materials and methods: This retrospective study included patients with intracranial ependymoma treated with PT or a hybrid proton-photon (PT-XT) approach at our centre between July 2020 and December 2023 with a minimum 12 month follow-up. Treatment approach was determined based on tumour relationship to the brainstem. Patient and tumour characteristics and treatment planning approaches were evaluated, and dosimetric data between PT and PT-XT approaches were compared. Outcomes including symptomatic brainstem injury (SBI) and asymptomatic radiographic changes (ARC) were assessed. Results: Fourteen patients were included, of which nine had posterior fossa ependymoma, with five treated using a hybrid PT-XT planning approach and four with PT alone. The hybrid PT-XT approach involved delivering 75 % of the treatment (0-45 Gy(RBE)) with PT and the remaining portion (45-59.4 Gy) with XT, addressing concerns regarding increased relative biological effectiveness of PT in the brainstem. While all plans adhered to the European Particle Therapy Network D Conclusion: Tailored planning approaches, depending on location and relationship to the brainstem, are essential when treating ependymoma patients. A hybrid PT-XT approach, is feasible in well-selected patients, demonstrating acceptable target coverage, brainstem doses, and to date no occurrence of symptomatic brainstem injury.