Two fractions staged Gammaknife radiosurgery for “large” cerebral metastases

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.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).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.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.The new 2-fractions-dose-staged GKRS concept seems to be a well-tolerated and effective treatment option for large cerebral metastases.