Gamma Knife stereotactic radiosurgery for intracranial hemangiopericytomas

The purpose of this study is to determine the efficacy of Gamma Knife stereotactic radiosurgery (GK SRS) for intracranial hemangiopericytomas, and to investigate the optimal dose for successful tumor control without adverse effects. We evaluated 17 hemangiopericytomas of nine patients treated with GK SRS between 1999 and 2008. The mean tumor volume was 2.2 cm(3) (range 0.2-9.9 cm(3)), and the mean and median marginal doses were 18.1 and 20 Gy (range 11-22 Gy), respectively, at the 50% isodose line. Mean clinical and radiological follow-up periods were 49 and 34 months, respectively. Successful tumor control was achieved in 14 of 17 lesions (82.4%) at time of last follow-up after GK SRS. Actuarial local tumor control rates at 1, 2, and 5 years after GK SRS were 100%, 84.6%, and 67.7%, respectively. No adverse effects, such as radiation necrosis or marked peritumoral edema, were observed in any patient. Marginal dose (a parts per thousand yen17 Gy) was the only statistically significant factor for local tumor control on univariate analysis. Extended analysis using lesion data available from previous studies revealed that higher marginal dose (a parts per thousand yen17 Gy) was also significant (P = 0.028). GK SRS provides an effective and safe adjuvant management option for patients with recurrent or residual hemangiopericytomas. Our results suggest that doses higher than previously used (around 15 Gy) are desirable to achieve better local tumor control of hemangiopericytomas. Close radiological follow-up is also necessary for early detection of small recurrent lesions.