Gamma Knife Radiosurgery Inhibits Angiogenesis of Meningiomas: In Vivo Rat Corneal Assay

OBJECTIVE: The aim of this study is to reveal inhibitory effect of gamma knife irradiation on angiogenesis of meningiomas using rat corneal angiogenesis assay. METHODS: A total of 72 rats were divided into three preliminary groups. Each group, consisting of 24 rats, was implanted to World Health Organization (WHO) grade I (typical), grade II (atypical), and grade III (malignant) meningioma. Each of these three preliminary groups of 24 rats, were then divided into four subgroups, each consisting of 6 rats and subsequently irradiated by gamma knife with dose prescriptions of 0, 14, 18, and 22 Gy. The numbers of vessels that developed around the micropockets of the corneas were counted and photographed on days 5, 10, 15, and 20. RESULTS: For WHO grade I meningiomas, 18 and 22 Gy doses (P < 0.001), and for grade II meningiomas, the 22-Gy (P 0.021) dose were found to inhibit tumor-induced angiogenesis compared with the radiation-free control group. For grade III meningiomas, there was no statistical difference with the control group in any of the doses applied. Our findings demonstrate that gamma knife irradiation may suppress the angiogenic activity of WHO grades I and II meningiomas but not of the grade III meningiomas. CONCLUSIONS: For the first time, this study provides an experimental data to show the antiangiogenic effect of gamma knife irradiation on meningiomas.