Fractionated Stereotactic Radiation Therapy for Orbital Optic Nerve Sheath Meningioma – a Single Institution Experience and a Short Review of the Literature

Optic nerve sheath meningioma (ONSM) is a rare orbital tumor that generally induces a slow progressive visual loss in affected patients. Radiotherapy (RT) has currently become the first choice to treat ONSM. In this study our experience in ONSM treatment with fractionated stereotactic radiotherapy (FSRT) is reported. Five patients with diagnosis of orbital ONSM were treated between April 2007 and December 2009 at the Radiation Oncology department of our institution. All patients underwent history and physical, and ophthalmic examinations. Orbital MRI was performed before and 6 weeks after treatment; thereafter every 6 months for the first 2 years. By previous stereotactic localization of the target, RT was delivered with 28 daily fraction of 1.8 Gy by multiple non coplanar arcs dynamically conformed by a micro multileaf-collimator. At diagnosis, in all 5 patients, visual acuity limitations of different degrees were found, while exophthalmos was present in 2, diplopy in 2, orbital pain in 1, and proptosis in 1. In all patients pre-treatment MRI showed an orbital mass involving the optic nerve. After radiotherapy, previous symptoms improved in all patients. However, after RT the MRI consistently showed a stationary status compared to the MRI before RT. At a median follow up of 26 months (range 9-37) all patients had a subjective and/or objective better visual performance than before RT without any evidence of disease progression. No late side effects were recorded. Accordingly to the current literature, our experience confirms the efficacy and the safety of FSRT in patients with orbital ONSM.