Control of growth of vestibular schwannomas with low-dose Gamma Knife surgery

Object. The treatment of solitary vestibular schwannomas by performing Gamma Knife surgery is well established. It has been reported that decreasing the surface dose reduces patient morbidity, especially facial weakness and numbness. The authors of this retrospective study examine patient data from a single center to determine if low-dose (<= 14 Gy) GKS controls tumor growth as effectively as higher doses (> 14 Gy). Methods. Based on the formula for ellipsoid volumes, the tumor volumes were calculated using measurements from MR images obtained at follow up in patients treated at the authors' center. Follow-up data were available in 159 patients with a mean age of 59.5 +/- 14.2 years at treatment. Fifty-six percent of the patients were women and 53.5% of the tumors were located on the right side of the brain. The mean tumor volume was 3.3 +/- 4.3 cm(3) with 10% of the tumors having volumes larger than 8 cm(3). After GKS, smaller tumors (>= 40% decrease in volume) were observed in 44.8% of patients treated with a low dose and in 48.8% treated with a high dose. Enlarged tumors (>= 40% increase in volume) were seen in 5.2% of the patients receiving a low dose and 2.3% of those receiving a high dose. These differences were not statistically significant. Patients who had been followed up for longer than 5 years after treatment had median residual volumes of only 28.2% of the starting volume in the low-dose group and 26% in the high-dose group, This difference was statistically not significant. Conclusions. No statistically significant differences were observed between tumors given low-dose radiation treatment and those given high-dose radiation treatment.