Session Item

To analyze a newly proposed prognostic model for patients with brain metastases treated with stereotactic radiosurgery (SRS) and compare to two alternate prognostic models (Score Index for Radiosurgery in Brain Metastases [SIR] and Basic Score for Brain Metastases [BS-BM]) in predicting overall survival (OS).

We analyzed the patients receiving Linac-based stereotactic radiosurgery between 2010 and 2020. Patient and oncologic factors including the changes in sizes of brain metastasis between the diagnostic and stereotactic magnetic resonance imaging (MRI) for SRS were collected. The associations between prognostic factors and OS were assessed using Cox proportional hazards model with backward elimination. The model consistency was checked by 500 bootstrap replications. Our prognostic score was calculated by evaluating the most statistically significant factors. Patients were grouped and compared according to our proposed score, SIR, and BS-BM.

Total 85 patients were included, and 67 (79%) of them had positive growth in the size of brain metastasis. The median follow-up duration was 20 months (interquartile range [IQR] 10-34 months). Overall survival for the whole cohort was 17 months (95% confidence intervals [CI], 12–22 months). We developed the prognostic model based on the most important predictors of OS: percentage change in lesion size per day between the diagnostic and stereotactic MRI (hazard ratios [HR] of ≥1% vs <1%, 2.33; 95% confidence interval [CI], 1.22–4.44), extracranial oligometastatic diseases (≤5 involvements) (HR, 0.27; 95% CI, 0.14–0.53), and the presence of neurological symptoms (HR, 2.91; 95% CI, 1.31–6.42). For our model, patients with scores 0, 1, 2, and 3 had a median OS of 3.7 (95% CI 0.8–not reached [NR]), 2.0 (95% CI 1.2–NR), 1.0 (95% CI 0.6–1.8), and 0.2 (95% CI 0.1–NR) years, respectively. Pairwise comparisons using Log-Rank tests showed statistically different survival except between score 0 and 1. The optimism-corrected c-index for the proposed model, SIR, and BS-BM were 0.681 (95% CI, 0.594–0.773), 0.560 (95% CI, 0.450–0.662), and 0.559 (95% CI, 0.461–0.657), respectively. 

Our model is useful to identify patients with brain metastasis treated with SRS with different OS. Its prognostic ability appeared slightly better than SIR and BS-BM in our cohort. However, further studies to validate our findings are needed.