(P036) The Significance of Different Dose Fractionations in the Management of Optic Nerve Sheath Meningioma

Veronica A. Finnegan, MD, Seung Hahn, MD, Anna Shapiro, MD, Luis Mejico, MD; SUNY Upstate Medical University

Background: Optic nerve sheath meningiomas (ONMs) typically present with unilateral vision loss, visual disturbance, and/or eye pain or pressure. The diagnosis is usually made by clinical and imaging findings without biopsy. ONMs are generally not amenable to surgery due to morbidity, visual deterioration. For this reason, radiation is often used as primary treatment. Different dose fractionations have been used, without clear consensus on optimal treatment. The number of fractions can also be influenced by accessibility to treatment centers and is a significant factor for patients in rural areas treated with conventional-dose fractionation, which requires over 5 weeks of treatment.

Materials and Methods: A retrospective review of patients treated with radiation therapy (RT) for ONMs was performed to analyze tumor control, symptom improvement, and treatment complications according to different dose fractionations. Patients had documented vision testing before and after treatment, which was performed by a neuro-ophthalmologist.

Results: Data were collected on 8 patients, 2 of whom had bilateral disease, for a total of 10 cases treated for ONM between 2006 and 2012. Vision loss was the presenting symptom in eight cases, one patient had eye pain, and the other was asymptomatic and was found to have an abnormal eye exam with increased optic nerve pressure. The patient who was asymptomatic had biopsy consistent with meningioma. Median follow-up was 43 months. Six optic nerve tumors were treated by conventional fractionation (≤ 2 Gy/fraction to a total dose of 45–54 Gy). They were considered standard fractionation. Four cases were treated with hypofractionated radiotherapy using 25 Gy in five fractions. All patients had local control based on the most recent imaging with MRI. In follow-up vision testing by neuro-ophthalmologic evaluation, 6 of 10 eyes achieved long-term vision improvement. Three patients had stable vision, and one had worse. With conventional fractionation, three of six had improvement, two were stable and one was worse. For the hypofractionated radiotherapy group, four of four had initial improvement, and three had long-term improvement. One patient developed radiation retinopathy 3 years after treatment, resulting in vision loss. In this case, the retina received full dose due to extension of the tumor. Six of nine patients, excluding the one who was asymptomatic, had resolution of subjective symptoms. Vision in the contralateral eye was unaffected in the majority of cases and actually improved in one patient, possibly due to radiotherapy to the area of involvement of the optic chiasm.

Conclusion: RT for ONM is an effective treatment to prevent visual deterioration and often improves visual loss that has already happened. Our study indicates that hypofractionated radiation is at least as effective as conventional radiation in preventing visual loss but seems to be more effective for improving visual changes caused by ONM. Hypofractionated radiation can be safely applied to patients with limited access to radiation centers. This should be further tested in a nationwide large-scale study in the future.