Development of a Prognostic Model for Overall Survival in Patients With Extracranial Oligometastatic Disease Treated With Stereotactic Body Radiation Therapy

Purpose: Patients with oligometastatic disease (OMD) can experience durable disease control with ablative therapy to all sites of disease. Stereotactic body radiation therapy (SBRT) is an important modality in the management of OMD, although a validated prognostic model for OMD treated with SBRT is currently lacking. The purpose of this study was to develop a prognostic model for overall survival (OS) in patients with OMD treated with SBRT. Methods and Materials: A multi-institutional database of patients with extracranial OMD treated with SBRT was used for model development. The final prognostic model was generated in a training set using recursive partitioning analysis representing 75% of the population. Model performance was evaluated in the reserved test set. Results: The analysis included 1033 patients. The median OS for the entire cohort was 44.2 months (95% confidence interval [CI], 39.2-48.8 months). The variables used in the regression tree, in order of importance, were primary histology, lung-only OMD on presentation, the timing of OMD presentation, and age at the start of SBRT. A full 5-category risk stratification system based on the terminal nodes possessed fair to good discriminative power with a Harrell concordance statistic of 0.683 (95% CI, 0.634-0.731) and a time-dependent area under the receiver operating characteristic curve of 0.709 (95% CI, 0.706-0.711) in the test set, with good calibration. A simplified risk stratification system consisting of 3 risk categories was also proposed for greater ease of use with comparable performance. Conclusions: A clinical prognostic model for OS in patients with extracranial OMD treated with SBRT has been developed and validated.