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

OBJECTIVES: To identify risk factors associated with early distant radiographic progression in patients undergoing stereotactic radiosurgery (SRS) for brain metastases (BM).

METHODS: Following Institutional Review Board approval, data of 1427 patients (4283 BM lesions) who were treated by SRS at the Cleveland Clinic for 2000-2012 were collected. Local tumor progression (LTP), distant tumor progression (DTP), and radiographic radiation necrosis (RN) were the primary endpoints. Patient, imaging, radiosurgery, and tumor variables and follow-up data were collected.

RESULTS: The median number of targets was 2 (range, 1-17); 45% of the patients had a single lesion. DTP was observed in 10% at 3 months and 19% at 6 months. 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 (odds ratio [OR], 0.83, 95% confidence interval [CI], 0.40-0.85 and OR, 0.85, 95% CI, 0.45-0.86 respectively; P < 0.05). Younger age (<65 years; P < 0.001), higher number of lesions (>1; P < 0.001), cumulative intracranial tumor volume (CITV) <2.75 cc (P = 0.023), type of SRS (upfront and salvage vs. boost; P < 0.001), and tumor pathology (radiosensitive; P < 0.001), were independent predictors of early distant tumor progression following SRS.

CONCLUSIONS: The number of target lesions and low CITV are both independent predictors of early DTP following SRS for BM. Radiosensitive tumor histology, younger age (<65 years), and SRS without previous whole-brain radiation therapy (upfront or salvage) were also predictors of early DTP.