Thirty years' experience with Gamma Knife surgery for metastases to the brain.

OBJECT: The aim of this study was to analyze factors influencing survival time and patterns of distant recurrences after Gamma Knife surgery (GKS) for metastases to the brain.
METHODS: Information was available for 1855 of 1921 patients who underwent GKS for single or multiple cerebral metastases at 4 different institutions during different time periods between 1975 and 2007. The total number of Gamma Knife treatments administered was 2448, an average of 1.32 treatments per patient. The median survival time was analyzed, related to patient and treatment parameters, and compared with published data following conventional fractionated whole-brain irradiation.
RESULTS: Twenty-five patients survived for longer than 10 years after GKS, and 23 are still alive. Age and primary tumor control were strongly related to survival time. Patients with single metastases had a longer survival than those with multiple metastases, but there was no difference in survival between patients with single and multiple metastases who had controlled primary disease. There were no significant differences in median survival time between patients with 2, 3-4, 5-8, or >8 metastases. The 5-year survival rate was 6% for the whole patient population, and 9% for patients with controlled primary disease. New hematogenous spread was a more significant problem than micrometastases in patients with longer survival.
CONCLUSIONS: Patient age and primary tumor control are more important factors in predicting median survival time than number of metastases to the brain. Long-term survivors are more common than previously assumed.