Adjuvant Gamma Knife radiosurgery following surgical resection of brain metastases: a 9-year retrospective cohort study

Given the potential morbidity of whole brain radiation therapy (WBRT), there has been an increasing trend to defer WBRT and deliver Gamma Knife stereotactic radiosurgery (GKS) to cerebral metastatic lesions. We analyzed our experience delivering GKS to the tumor cavity following surgical resection of brain metastases and compared our results to patients receiving WBRT after surgical resection of a metastatic lesion. We performed a retrospective review of patients undergoing surgical resection of at least one brain metastasis between December 1999 and December 2008. Both univariate and multivariate Cox proportional hazards regression were utilized to analyze the influence of various prognostic factors on survival. Twenty-five patients had a metastatic lesion resected followed by adjuvant GKS to the resection cavity while another 18 had surgical resection followed by WBRT. Aside from a disparity in gender distribution (72% of GKS patients were female while women only constituted 28% of the WBRT group), no significant differences existed between groups. The median survival for patients receiving GKS was 15.00 months as compared to 6.81 months among those receiving WBRT (P = 0.08). Univariate Cox regression analysis identified the number of metastases (HR 1.65, 95% CI 1.07-2.54, P = 0.02) and regional recurrence (RR 5.23, 95% CI 1.78-15.38, P = 0.003) as poor prognostic factors. Multivariate regression analysis showed that regional recurrence (HR 5.17, 95% CI 1.69-15.78, P = 0.004) was again strongly associated with worse survival. Although limited by the retrospective nature of our study and lack of some clinical measures, patients undergoing GKS to the resection cavity had a trend towards longer median survival.