Predictors of Adjuvant Radiotherapy Timing after Spine Surgery for Metastases

Introduction: Radiation following stabilization or decompression surgery for spinal metastases is generally standard of care; however, timing adjuvant radiation is still under debate. This study aims to elucidate factors associated with timing between surgery and radiation and help establish an optimal window for initiating radiation after spine surgery.

Methods: We conducted a retrospective review of patients who underwent radiation after spine surgery for metastases at a single-institution over 14-years. Patient demographics, medical comorbidities, performance status, metastatic disease burden, surgical approach and characteristics, post-operative outcomes, and adjuvant therapy were collected through chart review. Data were analyzed with multi-variable regression analysis using a gradient-boosted decision tree and random forest model, with forest importance used to measure predictiveness.

Results: 53 patients who completed radiotherapy after spine surgery for spinal metastases were included. 36 patients also underwent adjuvant systemic chemotherapy. Average patient age was 61.4 years. Median time of surgery after diagnosis of metastatic disease was 14 days. Median time from surgery to initiation of radiotherapy was 33 days. Median hospital length of stay was 9 days. Only 3 patients experienced wound complications. Surgeon preference and spine instrumentation were correlated with delayed initiation of adjuvant therapy. Factors most predictive for time between surgery and initiation of radiotherapy included: post-operative hospital length of stay (i = 0.106), patient characteristics including age (i = 0.093) and BMI (i = 0.084), preoperative ASA score (i = 0.065), and primary tumor location (i = 0.062). Gender (i = 0.001), spinal metastasis location (i = 0.001), and smoking status (i = 0.009) were the least predictive of adjuvant radiotherapy timing.

Conclusion : Timing of adjuvant radiotherapy is most predicted by medical comorbidities, patient health status, and primary disease characteristics. While the time period between surgery and radiation is often guided by surgeon preference and concern for wound healing, objective patient criteria may be used to determine optimal timing of post-operative radiotherapy.