Purpose: Proton beam therapy (PT) is of increasing interest especially in tumors in close proximity of critical structures like skull base meningioma. Treatment outcome and toxicity data collected in a prospective registry of a single institution are presented.
Methods: Between July 2013 and May 2018, 55 adult patients with meningioma with a median age of 55.7 y (20.1-79.6 y) were treated and were prospectively enrolled in the in-house registry ProReg. The cohort consisted of 15 male and 40 female patients. Histopathology included WHO °I (36, 65.5%) and WHO °II (8, 14.5%). Eleven patients (20%) received no biopsy. Twenty-two (40%) patients received definitive PT. Adjuvant PT was administered after gross total resection and subtotal resection in 8 (14.5%) and 25 (45.5%), respectively. The median total dose of PT was 54Gy (54-60Gy) applied in 27 (27-33) fractions. 
Results: The median follow-up time from the primary diagnose was 3 years (0.4 – 26.1 y) and after the end of PT  1 year (0-4.5 y). Local disease control was achieved in 52 patients (94.5%). Local recurrence occurred in 1 patient and 2 patients had local progress after treatment. All patients were alive at last follow-up. PT was well-tolerated. No new higher-grade (CTCAE ≥°3) acute toxicity occurred. Long-term follow-up after PT showed 1 new CTCAE °3 toxicity as increasing vision deficit due to tumor progression. 
Conclusion: Current data support good early tumor control and feasibility of PT in meningioma.

05 - Proton beam therapy for meningioma - treatment outcome and toxicity