Development and validation of a recursive partitioning analysis-based pretreatment decision-making tool identifying ideal candidates for spine stereotactic body radiation therapy.

Abstract

This study was aimed at developing and validating a decision-making tool predictive of overall survival (OS) for patients receiving stereotactic body radiation therapy (SBRT) for spinal metastases. Three hundred sixty-one patients at one institution were used for the training set, and 182 at a second institution were used for external validation. Treatments most commonly involved one or three fractions of spine SBRT. Exclusion criteria included proton therapy and benign histologies. The final model consisted of the following variables and scores: Spinal Instability Neoplastic Score (SINS) ≥ 6 (1), time from primary diagnosis < 21months (1), Eastern Cooperative Oncology Group (ECOG) performance status = 1 (1) or ECOG performance status > 1 (2), and >1 organ system involved (1). Each variable was an independent predictor of OS (p<.001), and each 1-point increase in the score was associated with a hazard ratio of 2.01 (95% confidence interval [CI], 1.79-2.25; p<.0001). The concordance value was 0.75 (95% CI, 0.71-0.78). The scores were discretized into three groups-favorable (score = 0-1), intermediate (score = 2), and poor survival (score = 3-5)-with 2-year OS rates of 84% (95% CI, 79%-90%), 46% (95% CI, 36%-59%), and 21% (95% CI, 14%-32%), respectively (p<.0001 for each). In the external validation set (182 patients), the score was also predictive of OS (p<.0001). Increasing SINS<zaq;6> was predictive of decreased OS as a continuous variable (p<.0001). This novel score is proposed as a decision-making tool to help to optimize patient selection for spine SBRT. SINS may be an independent predictor of OS.