Hypofractionated Radiosurgery for Perioptic Meningiomas: Current Practice, Principles, and Treatment Quandary

Perioptic meningiomas, defined as those in contact or adjacent (within a 2 or 3 mm distance) to the anterior optic pathways (AOP, optic nerves, and chiasm), are challenging lesions to manage with radiation ablative therapies due to the vicinity to the radiation-sensible optic apparatus. Because of the perceived risk of damaging the AOP with single-session stereotactic radiosurgery, hypofractionated radiation delivery regimens have been introduced since the last two decades. Hypofractionated radiosurgery involves the delivery of an ablative radiation dose in 2–5 large fractions at 24- or 12-h intervals and allows the surgeon to combine the high conformality and targeting accuracy of SRS platforms with the radiobiological advantages of dose fractionation. Various studies have investigated the safety and efficacy of hypofractionated radiosurgery for the treatment of perioptic meningiomas using the Gamma Knife, the CyberKnife, and linear accelerators. Overall, those studies have confirmed that hypofractionated stereotactic radiosurgery is effective in controlling the growth of perioptic meningiomas and is safe to the anterior optic pathways, though follow-up assessment periods and number of patients included remain limited. The aim of this chapter is to review the literature about stereotactic hypofractionated radiosurgery for the treatment of perioptic meningiomas. These outcomes are compared with those of alternative therapies including conventionally fractionated radiation therapy and single-session radiosurgery. Finally, the radiation tolerance of the optic pathways when using the different radiation delivery regimens is discussed.