Gamma knife stereotactic radiosurgery for patients with glioblastoma multiforme

OBJECTIVE: Stereotactic radiosurgery (SRS) has become an effective therapeutic modality for the treatment of patients with glioblastoma multiforme (GBM). This retrospective review evaluates the impact of SRS delivered on a gamma knife (GK) unit as an adjuvant therapy in the management of patients with GBM. METHODS: Between August 1993 and December 1998, 82 patients with pathologically confirmed GBM received external beam radiotherapy (EBRT) at the University of Maryland Medical Center. Of these 82 patients, 64 with a minimum follow-up duration of at least 1 month are the focus of this analysis. Of the 64 assessable patients, 33 patients were treated with EBRT alone (Group 1), and 31 patients received both EBRT plus a GK-SRS boost (Group 2). GK-SRS was administered to most patients within 6 weeks of the completion of EBRT. The median EBRT dose was 59.7 Gy (range, 28-70.2 Gy), and the median GK-SRS dose to the prescription volume was 17.1 Gy (range, 10-28 Gy). The median age of the study population was 50.4 years, and the median pretreatment Karnofsky performance status was 80. Patient-, tumor-, and treatment-related variables were analyzed by Cox regression analysis, and survival curves were generated by the Kaplan-Meier product limit. RESULTS: Median overall survival for the entire cohort was 16 months, and the actuarial survival rate at 1, 2, and 3 years were 67, 40, and 26%, respectively. When comparing age, Karnofsky performance status, extent of resection, and tumor volume, no statistical differences where discovered between Group 1 versus Group 2. When comparing the overall survival of Group 1 versus Group 2, the median survival was 13 months versus 25 months, respectively (P = 0.034). Age, Karnofsky performance status, and the addition of GK-SRS were all found to be significant predictors of overall survival via Cox regression analysis. No acute Grade 3 or Grade 4 toxicity was encountered. CONCLUSION: The addition of a GK-SRS boost in conjunction with surgery and EBRT significantly improved the overall survival time in this retrospective series of patients with GBM. A prospective, randomized validation of the benefit of SRS awaits the results of the recently completed Radiation Therapy Oncology Group's trial RTOG 93-05.