Fractionated Radiotherapy for Optic Nerve Sheath Meningiomas

Optic nerve sheath meningiomas (ONSM) are rare tumors of the meninges that surround the optic nerve as it enters the orbit. If left untreated, these benign tumors lead to progressive compression of the optic nerve and vascular compromise resulting in visual loss. Surgical resection of ONSM is associated with a high morbidity due to injury to the vascular supply of the optic nerve, with up to 94% of patients reporting worsened vision post-operatively. Fractionated radiotherapy is a non-invasive alternative to surgery for the treatment of ONSM that has demonstrated improved outcomes. The reported long-term tumor control rates approach 100%, with greater than 80% vision preservation or improvement after treatment. Recently, improved technology for delivery of radiotherapy, including stereotactic and three-dimensional conformal radiotherapy has emerged. The literature suggests that the modality of radiotherapy does not affect the outcomes as long as conformal targeting with a total dose of 50 Gy to 54 Gy and a fractional dose of less than 2.0 Gy is used. Radiosurgery is not generally used for ONSM due to the high toxicity to the optic nerve when high-dose single fraction radiation is given. Therefore, conformal fractionated radiotherapy appears to be the most effective treatment for ONSM, and should be used as a primary therapy unless there is a specific indication for surgical intervention.