Object The authors evaluated the results they obtained using Gamma Knife surgery (GKS) in patients with orbital tumors. Methods This is a retrospective clinical evaluation of 202 patients with orbital tumors who were treated with GKS between September 1995 and October 2008. The series included 84 men and 118 women with a mean age of 39.5 ± 14.6 years (range 5–85 years). The diagnoses were determined based on pathological analyses in 113 patients and presumed based on characteristic clinical and imaging findings in 89 patients. There were 84 meningiomas, 38 epithelial tumors of the lacrimal gland, 23 schwannomas, 18 malignant choroidal melanomas, 12 optic nerve gliomas, 11 orbital metastases, 10 pseudotumors of the orbit, 3 retinoblastomas, and 3 cases of fibromatosis. The median target volume was 5.4 cm3 (range 0.04–35.6 cm3). The tumor margin dose ranged from 10 to 40 Gy. Results At a median follow-up period of 34.5 ± 14.7 months (range 12–114 months), tumor shrinkage was observed in 118 patients (58.4%) and stable tumor size in 71 patients (35.1%). Regularly scheduled neuroimaging studies demonstrated evidence of tumor progression in only 13 patients (6.4%): 9 of these patients underwent repeated GKS and 4 received surgical treatment. Visual acuity was preserved in 129 patients. Seventy-two patients experienced some degree of improvement in vision. Severe deterioration of visual acuity was found in 18 of 147 patients who had useful vision before treatment. Nineteen patients (9.4%) experienced transient conjunctival edema; no other serious acute side effect was observed. Conclusions Gamma Knife surgery provides an effective management strategy in patients with orbital tumors; it achieves excellent preservation of neurological function and is associated with few treatment-related complications.

Object The goal of this study was to assess the long-term results of Gamma Knife surgery (GKS) in patients harboring an optic nerve sheath meningioma (ONSM). Methods Thirty patients harboring an ONSM were treated with GKS between 1998 and 2003. Gamma Knife surgery was performed as the sole treatment option in 21 of these patients and resection had been performed previously in 9 patients. The mean volume of the tumor at the time of GKS was 3.6 cm3 (range 1.4–9.7 cm3), and the mean prescription peripheral dose was 13.3 Gy (range 10–17 Gy). The mean number of isocenters used to treat these lesions was 8 (range 5–14 isocenters). Results At a median follow-up of 56 months, visual acuity improved in 11 patients, remained stable in 13 patients (including 4 patients who were completely blind before GKS), and deteriorated in 6 patients. Follow-up images were available in all patients and showed tumor regression in 20 patients and stable tumor in 8 patients. Persistent imaging evidence of progression was only present in 2 patients. With the exception of reversible conjunctival edema in 4 cases, no other serious acute side effect was observed. Conclusions Gamma Knife surgery provides long-term tumor control for ONSM. The results of this study add substantial evidence that GKS may definitely become a standard treatment approach in selected cases of ONSM.

ObjectThe authors sought to assess the results of Gamma Knife surgery (GKS) in patients with vestibular schwannomas (VSs).MethodsSeventy-four consecutive patients (33 men and 41 women) were evaluated by means of serial imaging studies, clinical examinations, and questionnaires. Nineteen patients had undergone resection of their VS. Facial nerve function was normal in 63 patients (85.1%) before GKS, and 63.5% of them had useful hearing. The prescription peripheral dose varied between 10 and 14 Gy (mean 12.27 ± 0.96 Gy); the corresponding central dose was 21 to 30 Gy (mean 24.9 ± 2.18 Gy). The mean volume of the tumor at GKS was 10.79 ± 5.52 ml (range 0.11–27.8 ml). A mean of eight isocenters (range 3–17) was used for treating these lesions.At a median follow-up period of 68.3 months (range 30–122 months), tumor shrinkage was observed in 60 patients (81.1%), and the tumor size was stable in 11 (14.8%). Persistent neuroimaging demonstrated evidence of progression in only three patients (4.1%): two underwent repeated GKS after an interval of 18 months and one continues to be observed. Five patients experienced trigeminal dysfunction: in three the dysfunction was transient and in the other two the dysfunction persists. Three patients suffered facial palsy. Useful hearing was preserved in 34 patients. Thirteen patients experienced some degree of hearing improvement. Deterioration of hearing was found in 13 of 62 patients who had Class I or II hearing before treatment.Conclusions Gamma Knife surgery prevents tumor growth; it achieves excellent neurological function preservation and produces few treatment-related complications.

Objective: To study the relationship between dose-volume effect and complication in gamma knife radiosurgery of intracranial meningiomas. Method: By using an integrated logistic formula to establish mathematical models, the authors analyzed the relationship between treatment volume and logistic probability for 15 Gy, and the relationship between prescribed dose and treatment volume in 3% logistic probability. Furthermore, 37 meningiomas treated by gamma knife radiosurgery were analyzed retrospectively to investigate how the 3% isoeffect curve impacted on complication. Result: There was a linear relation between treatment volume and logistic probability for 15 Gy. The regression formula was f(x) = 0.0042x + 0.0007. The 3% isoeffect curve indicated that the prescribed dose was inversely proportional to the treatment volume. During 16.3 months follow-up on average, 18 cases below the 3% isodose curve were without complication, but in 19 cases above the 3% isodose curve, 5 cases suffered complications, the difference being statistically significant. Conclusion: Dose selection in gamma knife radiosurgery is volume dependent. The 3% isodose curve may possibly be the guideline in gamma knife radiosurgery of meningiomas.