The Prognostic Role of Tumor Volume in the Outcome of Patients with Single Brain Metastasis After Stereotactic Radiosurgery

BACKGROUND: Patients with single brain metastasis (SBM) have better outcomes after stereotactic radiosurgery (SRS). We analyzed our SRS database to evaluate possible prognostic factors in patients with SBM. METHODS: A total of 584 patients with SBM were treated with SRS at our institution (2000-2012). Study end points were overall survival (OS), and distant and local intracranial progression-free survival (DPFS and LPFS, respectively). Multivariable analysis was performed to develop prognostic models. RESULTS: Median OS was 10.8 months. A total of 196 patients (36.7%) had distant progression and 102 patients (19.2%) had local progression. New SBM prognostic indices (SPIs) were devised for OS, DPFS, and LPFS. Graded prognostic assessment, neurologic symptoms (P=0.01), and tumor volume (P=0.02) were independently associated with OS. The SPI for OS was defined: unfavorable (OS, 7.3 months), intermediate (OS, 10.6 months), and favorable (OS, 19.8 months). For DPFS, age (P=0.0029), tumor volume (P=0.0002), and previous whole-brain radiotherapy (P=0.027) were prognostic and were used to define SPI for DPFS: favorable (6-month cumulative incidence failure=CIF], 10.9%), intermediate (6-month CIF, 16.7%), and unfavorable (6-month CIF, 26.0%) (P < 0.001). For LPFS, graded prognostic assessment (P=0.0012) and tumor volume (P=0.0004) were significant, and defined 2 groups in the LPFS SPI: unfavorable (6-month CIF, 12.3%) and favorable (6-month CIF, 6%) (P < 0.001). CONCLUSIONS: This is the largest series of patients with SBM treated with SRS analyzed for OS, LPFS, and DPFS. SPI was devised for end points. Tumor volume had a significant association with all 3 end points. Neurologic symptoms, age, and previous whole-brain radiotherapy were also found to be prognostic.