Volume-staged gamma knife surgery for the treatment of large skull base meningioma surrounding the optical apparatus: A snowman-shape design

BackgroundIn cases of meningioma surrounding the optical apparatus, this study sought to reduce the incidence of radiation-induced optical neuropathy resulting from gamma knife surgery (GKS) by dividing the treatment volume into 2 or 3 fractions.MethodsFour patients with a large skull base meningioma (1 male and 3 females; median age: 42 years; range: 33-43 yrs) were treated using volume-staged GKS. In stage I, the large basal part of the tumor (13.2 mL; range: 3.9-54.7 mL) was treated with a marginal dose of 13.5 Gy (range: 12-15 Gy). In stage II, treatment focused on the smaller upper portion of the tumor located close to the optical apparatus (4.3 mL; range: 1.5-16.2 mL), and the marginal dose was 9 Gy (range: 8-10 Gy).ResultsAll patients tolerated the treatments well, and tumors regressed over a median follow-up period of 100.5 months (range: 42-122 mos). Specifically, a 34-46% reduction in tumor volume was observed. All four patients presented improvements in the neurological deficits observed prior to GKS treatment, albeit to varying degrees. No adverse effects of radiation or new visual deterioration were observed during the follow-up period. Furthermore, no evidence of new endocrine dysfunction or new cranial nerve neuropathy was observed within a follow-up period of 100.5 months.ConclusionThe application of volume-staged GKS using snowman-shape design appears to be an effective approach to control tumor growth when treating benign meningiomas surrounding the optical apparatus. This approach enables the application of higher radiation dosages to facilitate tumor control while still preserving optic nerve function.