Stereotactic radiosurgery for atypical and anaplastic meningiomas.

Atypical and anaplastic meningiomas frequently recur in the relatively short-term after surgery. We have followed such postoperative cases by short-interval repeated MRI and have performed stereotactic radiosurgery (SRS) for progressive tumors as a salvage therapy. The objective of this report was assessment of the degree of tumor control, the risk of complications, and the presence of variables that predict outcome in patients treated with SRS for high-grade meningiomas. We reviewed 12 high-grade meningioma patients with 30 lesions treated by Linac-based SRS at Kyoto University Hospital between 1997 and 2002. They included 10 atypical meningiomas and 2 anaplastic ones according to the WHO classification. A mean tumor volume was 4.40cc and a mean marginal dose of SRS was 18.0 Gy (12-20 Gy). After a mean follow-up period of 43.4 months (6-84 months), 13 lesions had progression tumor within the SRS field and 6 lesions had out of the SRS field. Nine of 14 lesions, which were treated by SRS with a marginal dose of less than 20 Gy, had local recurrence in the SRS field. In contrast, four of 16 lesions, which were treated with marginal dose of 20 Gy, had local recurrence in the SRS field. The marginal dose <20 Gy was a statistically significant factor for a short-term progression in high-grade meningiomas (P = 0.0139). Five-year progression-free survival ratio in lesions treated with SRS below 20 Gy and 20 Gy were 29.4% and 63.1%, respectively. In conclusion, based on our findings, we suggest that recurrent high-grade meningiomas be treated by SRS with a marginal dose exceeding 20 Gy.