Gamma knife treatment strategy for metastatic brain tumors.

From 1993 to 2011, a total of 3,095 patients with brain metastases underwent Gamma Knife radiosurgery (GKS) at Tokyo Women's Medical University. Follow-up information on 2,283 of these patients was available for retrospective analysis. The cases were separated into three groups according to the treatment period, the model of the Gamma Knife used, main goals of treatment, and technical nuances of radiosurgery. In the latest cohort of patients treated with the Leksell Gamma Knife model 4C with automatic positioning system, an optimized treatment strategy was applied. It was based on highly selective dose planning, with the use of multiple small isocenters located within the bulk of the mass, which was done for prevention of the excessive irradiation of the perilesional brain and avoidance of its posttreatment edema. In cases of large cystic tumors, selective coverage of the contrast-enhancing capsule with chain-like application of multiple small isocenters was done. Introduction of the new treatment strategy did not affect the 1-year tumor control rate, which was consistently >90 %. However, it did result in a statistically significant reduction of severe posttreatment peritumoral brain edema (from 15.5 % to 6.3 %; P < 0.0001). In conclusion, recent technical and methodological achievements of GKS seemingly do not affect its high efficacy in cases of brain metastasis with regard to tumor control. However, it may result in a prominent reduction of treatment-associated -morbidity, which is particularly important in patients with large and/or critically located neoplasm.