Objective: To evaluate results of stereotactic radiotherapy for the treatment of optic nerve sheath meningioma (OM) at Ramathibodi Hospital.

Material and Method: Twelve patients with primary OM were treated with stereotactic radiation between 1998 and 2005. Five patients underwent surgery and had no light perception before radiation. All patients except one were treated with fractionated stereotactic radiotherapy (FSRT). Mean average dose of FSRT was 55.7 Gy; 180 cGy/fraction. One patient was treated with 15-Gy stereotactic radiosurgery.

Results: With a median follow-up of 34 months, there was no visual improvement in the five patients who were completely blind before radiation. Visual acuity improved in four patients and remained stable in two patients. Four of six patients had improved visual field, and five of six decreased in proptosis. Follow-up images were available in six patients, showing minimal tumor regression in five and stable in one. No serious acute side effect was observed. Vision became worse in one patient, who developed vitreous hemorrhage two years after FSRT.

Conclusion: Stereotactic radiotherapy is an effective treatment for primary OM. It provides tumor control and visual preservation with low risk of complications. However, more patients and further follow-up are needed for long-term outcomes.

Keywords: Stereotactic radiotherapy, Optic nerve, Optic nerve sheath, Meningioma