Efficacy and Safety of Proton Beam Therapy for Primary Optic Nerve Sheath Meningioma

PURPOSE: Management of optic nerve sheath meningiomas (ONSM) remains challenging. Photon radiation therapy (PhRT) is the most common treatment for sight-threatening ONSM. Proton beam therapy (PBT) is less commonly used because it is more expensive and because there are questions about its efficacy specifically in relation to ONSM. PBT has the theoretical advantage of reducing radiation exposure to adjacent structures. We report the visual outcome of patients with primary ONSM managed at the Fondation Ophtalmologique Adolphe de Rothschild, Paris, France, and treated with PBT at the Centre de Protonthérapie, Institut Curie, Orsay, France. METHODS: We conducted a retrospective review of all patients with primary ONSM who received PBT (either by itself or following surgery) between January 2006 and January 2019. Neuro-ophthalmic examinations were performed at presentation and after radiotherapy, and, when applicable, after surgery. Meningiomas were measured at the time of diagnosis and at each follow-up MRI examination. RESULTS: Sixty patients (50 women, 10 men; mean age, 45.2±11.1y) were included, of whom 29 underwent surgery. At presentation, 52 (87%) of them had decreased vision (average visual acuity: 0.6 logMAR). Fundus examination showed optic disc swelling (n=27; 46.5%), optic disc pallor (n=22; 37.9%), optic disc cupping (n=2; 3.4%), opto-ciliary shunt (n=8; 13.8%), or choroidal folds (n=5; 8.6%). Otherwise, it was unremarkable (n=7; 12.1%). After treatment, visual function was stable overall. Fundus examination showed pallor (n=47; 83.9%), swelling (n=3; 5.4%), or cupping (n=2; 3.4%) of the optic disc, or was unremarkable (n=5; 8.9%). The visual field of 8 patients worsened, while 3 developed asymptomatic retinal hemorrhages. Tumor shrunk significantly in 8 patients at 1 year after PBT and remained stable in size in all others. Patients with opto-ciliary shunts had significantly worse visual outcome than other patients. Retinal abnormalities were observed in 11 patients during follow-up. CONCLUSION: PBT alone or in association with surgery appears to be a safe and efficient treatment for ONSM, reducing the tumor size and stabilizing visual function. The risk of developing radiation retinopathy seems to be higher when patients had upfront surgery.