Quality of radiosurgery for single brain metastases with respect to treatment technology: a matched-pair analysis

Objective A comparison of treatment parameters and quality of clinical outcome in patients with single brain metastases treated with two different technologies for radiosurgery (Gamma Knife and CyberKnife). Methods Treatment parameters were statistically analyzed. Clinical outcome was assessed by matched-pair analysis based on the treatment device, differences in dose prescription, and the date of the treatment. Patients were matched according to their tumor size, age, gender, primary cancer, and Radiation Therapy Oncology Group score. Survival post-radiosurgery, local and distant tumor control, and complications were analyzed. Predictive factors were investigated. Results 423 single brain metastases were treated with Gamma Knife and 73 with CyberKnife. Tumor volumes were similar. The parameters minimum tumor dose, maximum tumor dose, prescription isodose volume, conformality index, homogeneity index, volume of tissue receiving a dose of 10 Gy or more were significantly larger in Gamma Knife group. Sixty-three patients were good matches. These showed the same pattern in parameters. Concerning the outcome analysis, only overall survival differed significantly between groups, twice as long with CyberKnife (P < 0.03). According to pooled data, dose was predictive of local failure, whole brain radiation therapy and chemotherapy were predictive of toxicity, the Radiation Therapy Oncology Group score was predictive of survival after radiosurgery, and date of treatment was predictive of overall survival. No factor predicted new brain metastases, including whole brain radiation therapy. Conclusions The most important result of this study was the finding that the obvious differences in treatment-related parameters between Gamma Knife and CyberKnife had no impact on the quality of the clinical outcome after radiosurgery. Survival time increased chronologically, presumably due to an intensified anti-cancer therapy in the more recent era of the CyberKnife treatments.