Introduction: Spine stereotactic radiosurgery (SRS) has emerged as a method to provide local control with minimal toxicity or interruption in systemic therapy to patients with spinal metastasis. Despite impressive local control, SRS has complications, the most studied of which is vertebral compression fractures (VCFs). Vertebral compression fractures following radiosurgery at the irradiated level have been reported at incidences ranging from 6-39%. 1-5 Thus far, studies have evaluated the incidence and risk factors for VCF at the level of the irradiated vertebral body and not for VCF occurring in vertebral bodies adjacent to the index level. However, VCFs above and below the irradiated level have occurred and physicians need to be aware of such potential side effects associated with SRS.

Methods: A retrospective review of 206 patients with a total of 239 lesions in the mobile spine treated with single fraction SRS to dose 24Gy from 2011 to 2014 at a single institution was performed. (Table 1) Clinical and pathologic factors were collected including evaluation of VCFs in adjacent levels to site of SRS. Cox regression univariate analysis modeling was performed with IBM SPSS software for all VCFs.

Results: Median follow up was 14.7 months (range, 0 – 64.0 months). Adjacent level VCFs were identified in 26 instances (10.8%). Of the adjacent VCFs, 14 fractures were associated with metastatic involvement , 5 fractures with both metastatic disease and instrumentation at the adjacent level, and 7 “pure” fractures (2.9%). The median time to fracture post-SRS was 14.0 months (range, 2.1 – 35.1 months) for all adjacent level VCFs. Images for patient case is shown in Figure 1. A cumulative incidence curve for the development of adjacent level VCFs are shown in Figure 2.

Conclusions: Adjacent level fractures are an infrequent occurrence in the setting of single fraction SRS to the mobile spine. Understanding the incidence is important for care in patients undergoing spinal SRS.

Patient Care: To help physicians avoid previously unknown complications after Stereotactic Radiosurgery to vertebral bodies

Learning Objectives: Understand that VCFs at vertebral levels adjacent to the site of SRS do occur and as such should be included and considered among other organs at risk.

References: 1. Boehling NS, Grosshans DR, Allen PK, McAleer MF, Burton AW, Azeem S, et al: Vertebral compression fracture risk after stereotactic body radiotherapy for spinal metastases. J Neurosurg Spine 16:379-386, 2012 2. Germano IM, Carai A, Pawha P, Blacksburg S, Lo YC, Green S: Clinical outcome of vertebral compression fracture after single fraction spine radiosurgery for spinal metastases. Clin Exp Metastasis 33:143-149, 2016 3. Jawad MS, Fahim DK, Gerszten PC, Flickinger JC, Sahgal A, Grills IS, et al: Vertebral compression fractures after stereotactic body radiation therapy: a large, multi-institutional, multinational evaluation. J Neurosurg Spine 24:928-936, 2016 4. Moussazadeh N, Lis E, Katsoulakis E, Kahn S, Svoboda M, DiStefano NM, et al: Five-Year Outcomes of High-Dose Single-Fraction Spinal Stereotactic Radiosurgery. Int J Radiat Oncol Biol Phys 93:361-367, 2015 5. Rose PS, Laufer I, Boland PJ, Hanover A, Bilsky MH, Yamada J, et al: Risk of fracture after single fraction image-guided intensity-modulated radiation therapy to spinal metastases. J Clin Oncol 27:5075-5079, 2009