Risk Factors for Radiotherapy Failure in the Treatment of Spinal Metastases

Study Design: Retrospective cohort study. Objective: To build a predictive model for risk factors for failure of radiation therapy, hypothesizing a higher SINS would correlate with failure. Methods: Patients with spinal metastasis being treated with radiation at a tertiary care academic center between September 2014 and October 2018 were identified. The primary outcome measure was radiation therapy failure as defined by persistent pain, need for re-irradiation, or surgical intervention. Risk factors were primary tumor type, Karnofsky and ECOG scores, time to treatment, biologically effective dose (BED) calculations using α/β ratio = 10, and radiation modality. A logistic regression was used to construct a prediction model for radiation therapy failure. Results: One hundred and seventy patients were included. Median follow up was 91.5 days. Forty-three patients failed radiation therapy. Of those patients, 10 required repeat radiation and 7 underwent surgery. Thirty-six patients reported no pain relief, including some that required re-irradiation and surgery. Total SINS score for those who failed reduction therapy was <7 for 27 patients (62.8%), between 7-12 for 14 patients (32.6%), and >12 for 2 patients (4.6%). In the final prediction model, BED (OR.451 for BED > 43 compared to BED ≤ 43; P =.174), Karnofksy score (OR.736 for every 10 unit increase in Karnofksy score; P =.008), and gender (OR 2.147 for male compared to female; P =.053) are associated with risk of radiation failure (AUC.695). A statistically significant association between SINS score and radiation therapy failure was not found. Conclusions: In the multivariable model, BED ≤ 43, lower Karnofksy score, and male gender are predictive for radiotherapy failure. SINS score was among the candidate risk factors included in multivariable model building procedure, but it was not selected in the final model. Level of Evidence: Prognostic level III.