Vertebral fracture following primary stereotactic body radiation therapy for spinal bone metastases: a decade of experience

OBJECTIVE The aim of this retrospective study was to comprehensively evaluate the factors that contribute to and protect against the occurrence of vertebral fracture (VF) following stereotactic body radiation therapy (SBRT) for the treatment of spinal bone metastasis (SBM). METHODS This study focused on adult patients who underwent primary SBRT for management of solid tumor SBMs from March 2012 to January 2023 with detailed follow-up medical records for at least 6 months. Target volume delineation for sacral and spinal SBRT was conducted in accordance with International Spine Radiosurgery Consortium guidelines and international consensus recommendations. Patients with SBM showing local progression during the follow-up period were excluded. The Spine Instability Neoplastic Score (SINS) was used to assess the relationship between various factors and the occurrence of post-SBRT VF. RESULTS A total of 304 patients (178 male, median age 65 years) with 450 SBMs involving 557 vertebrae were analyzed. The overall occurrence rate of VF, including post-SBRT VFs on SBRT-treated vertebrae and adjacent VFs (AVFs), was 16.6%. Post-SBRT VFs accounted for 15.6% of cases, while AVFs constituted 3.3%. Post-SBRT VFs predominantly exhibited a biconcave shape. Key factors associated with the development of post-SBRT VF included SBMs in the lumbar segment, spinal instability (SINS ≥ 7), the presence of pre-SBRT VF, and a higher radiation dose (biologically effective doses [BED 3 ] ≥ 153.3 Gy). The use of antiresorptive agents, including bisphosphonates and denosumab, significantly reduced the occurrence rate of post-SBRT VF, with denosumab showing a particularly enhanced protective effect. Pain relief and recalcification of SBMs following SBRT were also observed. CONCLUSIONS This study offers valuable insights into the occurrence of post-SBRT VF in SBM. While post-SBRT VF remains a significant concern in SBRT treatment, the potential for remineralization in SBM provides a promising avenue for enhancing spinal stability over time.