To determine the long-term outcomes and prognostic factors in benign intracranial meningiomas treated with gamma knife stereotactic radiosurgery (GK-SRS).

Between 1992 and 2000, 162 patients with benign meningiomas were treated with GK-SRS at the University of Maryland Medical Center. Complete follow-up was available in 137 patients. All patients underwent magnetic resonance imaging (MRI)-based treatment planning. Serial MRIs and clinical exams were performed to assess tumor response. GK-SRS was the primary treatment in 85 patients (62%), whereas 52 patients (48%) had prior surgical resections. The median prescribed dose was 14 Gy (range, 4-25 Gy) to the 50% isodose line. The median tumor volume, treatment volume, and conformity index were 4.5 cc (range, 0.32-80.0 cc), 6.3 cc (range, 1.0-75.2 cc), and 1.34 (range, 0.65-3.16), respectively. The median follow-up for the entire cohort was 4.5 years (range, 0.33-10.5 years). The following factors were included in the statistical analysis for disease-free survival (DFS) and overall survival (OS): sex, age, dose, gross tumor volume (GTV), conformity index (CI), and dural tail coverage.

Serial MRI analysis was available in 121 patients (88.3%). Decrease in tumor size was observed in 34 patients (28.1%), whereas there was no change in 77 patients (63.6%), for a crude radiographic control rate of 91.7%. Increase in tumor size was seen in 10 patients (8.3%). New neurologic deficits attributed to the treatment developed in 10 patients (8.3%). The mean DFS and OS for the entire cohort are 4.6 years and 5.0 years, respectively. The 5-year actuarial DFS and OS were 86.2% and 91.0%, respectively. Univariate analysis revealed GTV, sex, CI, and dural tail treatment to be significant prognostic factors. Patients with GTV < or =10 cc also had longer survivals, with the 5-years DFS and OS of 91.9% vs. 68.0% (p = 0.038) and 100% vs. 59.7% (p = 0.0001), respectively. The 5-years actuarial DFS and OS for females vs. males were 90.2% vs. 74.2% (p = 0.0094) and 91.6% vs. 89.1% (p = 0.016), respectively. Patients with CI > or =1.4 achieved a longer DFS, with a 5-year DFS of 95.2% vs. 77.3% (p = 0.01). Patients who had the dural tail treated also had higher 5-year DFS (96.0% vs. 77.9%, p = 0.038). Patients with lower conformity (i.e., CI > or =1.4) tended to have the dural tail covered in the prescription isodose line (p = 0.04). The only factor significant in the multivariate analysis was for patients with GTV >10 cc, who had a worse DFS (hazard ratio 4.58, p = 0.05).

This report adds to the literature that supports the efficacy and safety of GK-SRS in the management of patients with benign intracranial meningiomas. Our report identified male patients, patients with a CI <1.4, and tumor size greater than 10 cc to have a worse prognosis. Patients who were treated with less conformal plans to cover the dural tail had better outcomes. Our data clearly demonstrate the need to adequately cover the dural tail in patients treated with GK-SRS for benign intracranial meningiomas.