Introduction: Vertebral compression fracture (VCF) is increasingly being observed post-spine SBRT. A recent SINS classification was developed to segregate patients into the unstable, potentially unstable and stable risk categories but has yet to be clinically validated. The aim of this study was to determine the risk of VCF post-spine SBRT, and identify if SINS in addition to SBRT specific clinical and dosimetric factors were predictive for VCF.
Methods: We retrospectively scored 167 spinal segments in 100 patients treated with spine SBRT according to SINS specific criteria. In addition, we evaluated the presence of paraspinal extension, prior-radiation, dose per fraction (=20Gy vs <20 Gy), age and histology. The median total dose was 24 Gy (range, 8-35Gy), and number of fractions 3 (range, 1- 5 fractions). Baseline spine magnetic resonance imaging (MRI) and computed tomography (CT) at baseline were compared to subsequent imaging at q2-3 monthly intervals. Post-operative patients and patients who recurred prior to any VCF were excluded.
Results: Patients were classified by SINS as stable (57%) or potentially unstable (43%) at baseline. The median follow-up was 7.4 months (range, 0.4–37.3 months). Nineteen fractures (11%) were identified, and 12 (63%) were de novo and 7 (37%) were fractures that had progressed (FP). The mean and median time to fracture post-SBRT were 3.3 and 2 months, respectively (range, 0.5-21.6 month). The one-year fracture-free probability (FFP) was 87.3%. Multivariate analysis confirmed that alignment (p=0.0003, HR 0.09), lytic lesion (p 0.007, HR 0.082), primary histologic type, and dose per fraction >20Gy (p 0.004, HR 8.2) were the only significant predictors of VCF.
Conclusions: Presence of deformity and lytic tumor were the only predictive factors of VCF based on the original SINS criteria. Patients treated with =20 Gy in a single fraction and spinal metastases from liver and lung primaries were also at a higher risk of VCF.
Patient Care: Helping to clinically validate SINS criteria and trying to predict the group of patients at high risk of fracture after SBRT.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Understand the SINS classification, 2)Identify potential causes to new vertebral body fracture after spinal radiation