[Results of fractionated targeted proton beam therapy in the treatment of primary optic nerve sheath meningioma]

Introduction: Optic nerve sheath meningioma (ONSM) is a common benign neoplasm arising from the arachnoid tissue encapsulating the optic nerve and affects mainly middle aged women. It is a slow-growing tumor for which there is still no consensus on treatment.

Purpose: To evaluate the safety and efficacy of fractionated targeted proton beam therapy (PBT) in the treatment of ONSM and to define its role in the treatment of these tumors.

Methods and materials: We performed a retrospective analysis of 15 patients (13 women and 2 men), mean age 41.8 years, presenting with primary ONSM, followed at the Fondation Ophtalmologique Adolphe de Rothschild (Paris) between September 2006 and August 2013. After a multidisciplinary consultation, all were treated with PBT at a total dose of 52.2 Gy Eco, in fractions of 1.8 Gy Eco, at the Institut Curie (Paris). Patients underwent standardized follow-up including ophthalmologic examinations, visual field testing and imaging every 6 months. Study parameters were post-treatment visual acuity, tumor size on MRI, and treatment side effects

Results: We separated the patients into 3 distinct groups: patients treated by PBT after an observation period (4/15), patients treated by PBT after primary surgery (5/15) and patients treated by PBT as primary treatment (6/15). Visual acuity improved in 3 cases, deteriorated in 1 and remained stable in 11 cases. Tumor size on MRI remained stable in 100 % of cases following PBT. No serious adverse effects were recorded after a mean follow-up of 22.4 months (8-79 months).

Conclusion: Our experience confirms the efficacy and the safety of proton beam therapy in patients with ONSM. PBT presents a promising alternative to surgery and conventional radiotherapy in the treatment of the MGNO. It seems to be effective in controlling tumor size and stabilizing visual function, at the cost of very low toxicity. Additional studies are needed to accurately determine the decision-making criteria and the ideal timing of this treatment.