LMAP-11 CYSTIC BRAIN METASTASES OUTCOMES FOLLOWING GAMMA KNIFE RADIOTHERAPY

Abstract

Abstract BACKGROUND The response of cystic brain metastases (BMets) to radiotherapy is poorly understood, with conflicting results regarding local control (LC), overall survival (OS), and treatment-related toxicity. This study aims to examine the role of Gamma Knife (GK) in managing cystic BMets. METHODS Volumetric analysis was conducted to measure tumor and edema volume at the time of GK and follow-up MRI studies. We evaluated the association of 4 variables with survival using Cox regression analysis and used the Kaplan-Meier method to estimate median survival times (MST). RESULTS Between 2016 and 2021, 54 patients with 83 cystic BMets were treated with GK at our institution. Lung cancer was the most common pathology (51.9%), followed by breast (13.0%). The mean target volume was 2.7 cc (range, 0.1-39.0 cc) and the mean edema volume was 13.9 cc (range, 0-165.5 cc). The median prescription dose of single fraction and fractionated GK was 20 Gy (range, 14-27.5 Gy). With a median follow-up of 8.9 months, MST was 11.1 months, OS was 33.3%, and the one-year LC rate was 75.9%. GK was associated with decreased tumor and edema volumes over time, although 68.5% of patients required steroids post-GK. Patients whose tumors grew beyond baseline following GK received significantly more pre-GK whole-brain radiation therapy (WBRT) than those whose tumors declined following GK. Higher age at diagnosis of BMets and pre-GK systemic therapy were associated with worse survival, with an MST of 7.8 months in patients who received it compared to 23.3 months in those who did not. CONCLUSIONS Pre-GK WBRT may select for BMets with increased radioresistance. This study highlights the ability of GK to control cystic BMets with the cost of high post-treatment steroid use.