ZAP-X Stereotactic Radiosurgery for Optic Nerve Sheath Meningioma: A Case Report.

Primary optic nerve sheath meningiomas (ONSMs) are benign tumors and are a common cause of optic neuropathy due to compression of the optic nerve. Management of this tumor can be surgery or radiotherapy, but radiotherapy is the preferred treatment modality due to the risk of damage to the vasculature and resulting vision loss in surgery. The ZAP-X (ZAP Surgical Systems, Inc., San Carlos, CA) is currently the newest cranial stereotactic radiosurgery (SRS) platform. There are no reports describing its use or outcomes for ONSM. We present the case of the first documented patient to undergo ZAP-X SRS for the treatment of a primary ONSM.  The patient was a 68-year-old woman with a 0.27 cm3 enhancing lesion centered along the left optic nerve near the orbital apex with unilateral fluid distention of the left optic nerve sheath. The treatment plan consisted of six isocenters placed in the target and with a prescription dose of 2500 cGy in five fractions at the 61% isodose line. The maximum dose to 0.035 cm3 (D0.035cc) of the left and right optic nerves was 1454.9 and 26.4 cGy, respectively. Conformity and gradient indexes were 1.638 and 3.451, respectively. The patient tolerated the procedure well with no complications. Six months post-treatment, the patient had completely resolved left eye pain and pressure, with significantly reduced proptosis and a 44% reduction in tumor volume with no vasogenic edema. This case presents the successful use of ZAP-X SRS for the treatment of ONSM. Although requiring further investigation, such studies are needed to define the long-term efficacy of the platform.