366 Cumulative Intracranial Tumor Volume and Number of Brain Metastasis as Predictors of Developing New Lesions after Stereotactic Radiosurgery for Brain Metastasis

Abstract

Abstract INTRODUCTION The aim of our study was to identify risk factors associated with distant radiographic progression in patients undergoing stereotactic radiosurgery (SRS) for brain metastases (BM). METHODS Following IRB approval, data of 1427 patients (4283 BM lesions) who were treated using SRS at Cleveland Clinic from 2000–2012 were collected. Distant tumor progression at 3 and 6 months were the primary end points and correlated to patient related variables. Logistic regression and competing risk models were used for data analysis. RESULTS >The median number of targets was 2 (range 1–17) with 45% of patients having a single lesion. 45.9% of patient had lesions >2 cm in size and median total intracranial tumor volume was 2.6 cc (range 0.03-83cc). Overall, 4% and 9% of patients had local progression in 3 and 6 months, respectively. Distant progression was observed in 10% and 19% at 3 and 6 months. Patients with 2–4 target lesions were more likely to develop new lesions compared to those with single lesions at 3 months (OR: 0.84, P < 0.001) and 6 months (OR: 0.87, 0 = 0.014). Similarly, patients with 5–10 target lesions for SRS were more likely to develop new lesions at both 3 and 6 months compared to those with 2–4 lesions (OR: 0.83, CI: 0.40-0.85 and OR:0.85, CI: 0.45-0.86 respectively, P < 0.05). Higher number of lesions (>5), cumulative intracranial tumor volume (CITV) (= 2.75 cc), radiographic progression after SRS, type of SRS (boost versus upfront and salvage) and tumor pathology (radio resistant) were independent predictors of distant tumor progression following SRS. CONCLUSION Number of target lesions (>5) and CITV ( = 2.75 cc) are both independent predictors of distant tumor progression following SRS for BM at first and second follow up (3 and 6 months after SRS). Radio sensitivity of tumor and addition of WBRT are also predictors of distant intracranial progression.