Two fractions staged Gammaknife radiosurgery for "large" cerebral metastases

Background: Gammaknife radiosurgery (GKRS) is a valuable option to control cerebral metastases. However, the risk (adverse radiation effect (ARE))-benefit (local control (LC)) ratio switches when the target is too large.Objective: In order to balance this ratio, two fractions staged GKRS protocol was conducted for "large" cerebral metastases. The aim of this study is to evaluate the outcome (LC, ARE).Methods: A total of 39 large cerebral metastases in 35 patients were treated. The initial mean tumor volume was 14.6 cc [6.1; 35.8]. The prescription margin dose was 12 Gy on the 50% isodose line, with 2 weeks between them. A majority of primary cancer were from lung (43%), melanoma (20%) or breast (17%) origin. The mean age was 63 years old (31-89). Mean Graded Prognostic Assessment (GPA) was 2. Results: At the second fraction, mean tumor volume was 10.3 cc [1.9-27.4]. The mean percentage of volume variation for decreasing lesions was 29%. At last follow-up, mean tumor volume was 7.4 cc [0-25.2]; 34 lesions decreased volume (mean 35%). A decreased volume of more than 45% after first stage GKRS was able to predict a long-term local response to staged GKRS treatment. Local control rate at 6 months and 1 year was 87.3% and 75% respectively. The rate of ARE was 7.7%. No predictive factor of local control or ARE was found in a univariate analysis.Conclusion: The new 2-fractions-dose-staged GKRS concept seems to be a well-tolerated and effective treatment option for large cerebral metastases.