P18.03.a hypofractionation with optimized stereotactic radiosurgery planning for skull base perioptic meningiomas

Abstract BACKGROUND Skull base perioptic meningiomas are challenging for stereotactic radiosurgery (SRS). The therapeutic window between tumor control and normal tissue complication is extremely narrow in these tumors, especially of large volume and/or in close proximity to the optic apparatus (OA). To minimize the risk of radiation toxicity, we optimized our SRS plans in terms of both steeper dose fall-off and dose-volume constraints for OA and delivered hypofractionation treatment. MATERIAL AND METHODS Thirty-one patients had been treated with hypofractionated SRS using the CyberKnife for perioptic meningiomas > 10 cm3 in volume (median 18.9 cm3). Tumor locations were cavernous sinus (n=7), petroclival (n=6), and tentorial edge (n=6). Optimization in SRS planning was carried in two aspects: 1) for steeper dose fall-off, multiple virtual shells outside the target were introduced and appropriate dose limits (formulated from our own Gamma Knife data) were applied; and 2) to minimize the risk of optic neuropathy, dose-volume constraints for OA (from AAPM TG101) were applied. SRS was delivered in five daily fractions with a median cumulative dose 27.8 Gy. RESULTS With a median follow-up of 33 months, tumor control was achieved in 28 of 31 patients (90.3%). Treatment response on MRI included partial response (volume decrease > 20%) in 17 patients, stable in 11, and progression (volume increase > 20%) in 3. Neurological symptoms improved in 10 patients, unchanged in 20, and worsened in 1. CONCLUSION Our current results show a promising role of hypofractionated SRS with optimization in steeper dose fall-off and dose-volume constraints for OA for large-sized skull base perioptic megningiomas in terms of both tumor control and neurological outcomes.