Stereotactic intensity-modulated radiotherapy for skull base meningioma using the HybridArc with Novalis STx system

Skull base meningiomas are often difficult to remove completely with preserved nerve function and may require radiation therapy. However, the Gamma Knife is unsuitable for large tumor volume or the optic nerve, which is difficult to identify on imaging. We report the results of stereotactic radiotherapy with HybridArc using Novalis STx for skull base meningiomas. We retrospectively examined 28 patients with skull base meningioma who underwent stereotactic radiotherapy (54 Gy/30 fractions) with HybridArc. The 28 patients, nine males and 19 females, were aged 31–83 years (mean 58.4 years), and the tumor volume was 2.6–97.1 mL (mean 29.7 mL). HybridArc irradiation was performed with D95 54 Gy/30 fractions for all patients with a median follow-up period of 36.0 months (range: 12–78 months). Tumor control rates at 1, 2, and 5 years after radiotherapy were 92.6%, 89.1%, and 82.8%, respectively. Only one non-atypical meningioma remained uncontrolled; thus, the tumor control rate for non-atypical meningioma at 1, 2, and 5 years was 94.1%. Tumor control rates for atypical meningioma at 1, 2, and 5 years were 85.7%, 71.4%, and 53.6%, respectively, significantly worse than for non-atypical meningiomas (P = 0.0395). Radiation injury was observed in two cases (7.1%). Visual field defects were observed in 16 patients, and diplopia in 6. Visual field and diplopia improvements were achieved in 5 and 2 patients, respectively (with overlap). Stereotactic radiotherapy (54 Gy/30 fractions) with HybridArc using Novalis STx is a safe and effective approach for relatively large skull base meningiomas.