P12.01 Active beam scanning proton therapy for intracranial meningiomas: early treatment outcomes from Trento proton therapy center

Abstract

PURPOSE: To report preliminary results of active beam scanning proton therapy (PT) for intracranial meningiomas. MATHERIAL/METHODS: Twenty patients (pts) with meningiomas (histologically proven 16/20) were treated with PT between January 2015 and October 2016. Median age was 63 years (range, 43-82) while KPS ranged between 60 and 100 (median 80); 16 were female (80%), and 4 were male (20%). For patients who underwent surgery, 6 patients had a diagnosis of World Health Organization (WHO) Grade I, 6 of WHO grade II, and 4 of a WHO Grade III. In 4 patients diagnosis was based on the typical imaging appearance of a benign meningioma. All but one pts with grade II/ III lesions had a tumor pattern of meningiomatosis. Thirteen (65%) pts had skull base lesions. For benign meningiomas, total doses of 50-54 Gy(relative biologic effectiveness [RBE]) were applied. Grade II lesions, were treated with 60 GyRBE while grade III tumors received a boost up to 66 GyRBE in case of gross residual tumor. Four patients were treated as re-irradiation (range, 50.4-66 GyRBE). All the treatments were delivered at 1.8-2 GyRBE per fraction. All pts were treated with active beam scanning PT using 3-4 fields with single field optimization technique. Treatment planning was based on MRI. Eleven pts (55%) received also 68-Ga-DOTATOC-PET. Gross tumor volume ranged from 1 to 61 cc, while clinical target volume varied between 2 and 195 cc. Toxicity was assessed according to Common Terminology Criteria for Adverse Events version 4.0. Mean follow-up time was 6 months (range, 1-21). RESULTS: All pts completed the treatment without breaks. Registered acute side effects include grade 1 (15%) and grade 2 (20%) skin erythema, grade 2 (25%) alopecia, grade 1 (55%) fatigue, grade 1 (10%) and grade 2 (5%) conjunctivitis, grade 1 (15%) pain, grade 1 (15%) blurred vision, grade 1 (30%) headache, and grade 2 (10%) skin hyperpigmentation. There were no grade 3 or higher acute toxicities. Registered late side effects include grade 1 (5%) and grade 2 (30%) alopecia, grade 1 (10%) and grade 2 (10%) fatigue, grade 1 (15%) and grade 2 (5%) headache, grade 1 (5%) dizziness, grade 1 (10%) blurred vision, grade 1 (5%) and grade 2 (5%) pain, grade 1 (5%) dry eye, and grade 1 (10%) skin hyperpigmentation. During follow-up one pts (5%) who previously underwent 3 surgeries and 3 stereotactic radiation treatments developed radionecrosis (diagnosed at imaging) with no symptoms and no need of steroids. There were no grade 3 or higher late toxicities. Currently, absolute tumor control is 95%. One WHO III pts who previously underwent 2 surgeries and 1 stereotactic radiation treatment presented with both local and systemic tumor recurrence 5 months after PT. CONCLUSIONS: PT is feasible and safe treatment for pts with untreated, recurrent, or incompletely resected intracranial meningiomas. Longer follow-up is necessary to assess definitive efficacy.