Clinical Outcomes of Stereotactic Body Radiotherapy for Spinal Metastases with Paraspinal Extension

Purpose: SBRT for spinal column metastases with paraspinal extension poses a challenge for local control. However, data is limited. The purpose of this study is to better characterize patterns of local recurrence in this patient population with the goal of improving outcomes. Methods: Patients with spinal metastases with paraspinal extension treated with SBRT at a single institution from 2009–2021 were reviewed. Sites with previous surgery and/or radiation were included. Univariate analysis of size, PTV shape, previous fracture, multiple vertebral levels, muscle invasion, organ abutment, and dosimetric variables in relation to time-to-local failure (LF) was performed. Results: Seventy-six paraspinal masses were included in the analysis. Median follow-up period was 11.8 months. Seventy-six percent of thoracic paraspinal masses involved adjacent ribs. Twenty-one percent of paraspinal masses abutted organs, 18% had muscle invasion. The most common prescription for both radiation naive and re-irradiation treatments was 2700 cGy in 3 fractions. The 12-month incidence of local failure (LF) was 30% overall and 29.4% for re-irradiated sites. Forty percent of LFs involved the paraspinal region. No analyzed variables were significantly associated with LF events, PTV > 225cc and PTV shape (donut) trended toward significance (p = 0.08 and 0.07). Conclusion: While clinical and dosimetric variables did not show significant associations with LF, a large portion of LF occurrences were observed within the paraspinal region, suggesting that a generous asymmetrical expansion in the direction of paraspinal disease may help improve outcomes. Nonetheless, this study emphasizes the importance of refining treatment approaches for this population.