Introduction: A staple of current treatment paradigm of spinal metastasis is radiosurgery as the primary modality, reserving surgery for high­grade epidural spinal cord compression or spinal instability. Multiple studies report vertebral body compression fracture rates from 11­39% after SBRT. Reports of patients’ pain control ranged from 52­85% at 12 months and local control rates of 87­95% at 6 months to 73­92% at 12 months. Studies have shown that with high treatment doses the fracture rates are higher. We describe our experience of low­dose SBRT for spinal metastasis with fracture rates, local and pain control.

Methods: This is a retrospective, single institution analysis of 134 patients (316 spinal segments) undergoing SBRT for spinal metastases from 2010­ 2015. Fracture rates were assessed on follow­up CT. Local control analysis conducted with Kaplan­Meier statistics.

Results: 127 patients (287 spinal segments) were included in the analysis. Median age 67 years. Location of tumors were 13% cervical, 49% thoracic, 34% lumbar, 4% sacral. Tumor histology was 57.8% radiosensitive and 42.2% radioresistant. Treatment doses were: 13­-20Gy single­-fraction (52%); 16­-27Gy 3-­fraction (37%); and 25­-40Gy 5­-fraction (11%). 19% spinal levels required separation surgery for high­-grade epidural-spinal-cord-compression. Patient-reported pain scores showed 36% improved, 43% stable, and 20% worsened. Fracture rates were 9.06%. Local control rates were 83% at 6­months and 76% at 12­months. Local failure rates better in single­fraction versus hypofractionated (HR=2.63; p=0.01). There was no difference between radiosensitive and radioresistant tumors in local control (HR=1.59; p=0.26). Better local control with SINS 0-6 vs >7 (HR=4.25; p=0.004).

Conclusions: Low­dose SBRT can achieve durable radiologic local and pain control in spinal metastatic disease. Fracture rates can be lowered with this approach, while still balancing appropriate local and pain control. Single­ fraction treatment is superior to multi­fraction regimens. Multidisciplinary treatment teams can entertain low­dose regimens for patients at higher risk for vertebral body fractures.

Patient Care: Patients at higher risks of vertebral body fractures can be administered low dose radiation to minimize fractures. This can lead to improved pain and quality of life which is paramount in patients with metastatic disease.

Learning Objectives: (1) Describe the effect of SBRT dose on vertebral body fracture rates. (2) Identify effective treatment options to reduce vertebral body fracture rates. (3) Identify the ability to of low­dose SBRT to obtain similar local control and pain control as higher dose­SBRT.

References: 1. Chawla S, Schell MC, Milano MT: Stereotactic body radiation for the spine: a review. Am J Clin Oncol 2013, 36:630–6. New response evaluation criteria in solid tumours: Revised RECIST guideline (version 1.1) . 2. Bilsky MH, Laufer I, Fourney DR, Groff M, Schmidt MH, Varga PP, Vrionis FD, Yamada Y, Gerszten PC, Kuklo TR: Reliability analysis of the epidural spinal cord compression scale. J Neurosurg Spine 2010, 13:324–8. 3. Fisher CG, Schouten R, Versteeg AL, Boriani S, Varga PP, Rhines LD, Kawahara N, Fourney D, Weir L, Reynolds JJ, Sahgal A, Fehlings MG, Gokaslan ZL: Reliability of the Spinal Instability Neoplastic Score (SINS) among radiation oncologists: an assessment of instability secondary to spinal metastases. Radiat Oncol 2014, 9:69. 4. Fourney DR, Frangou EM, Ryken TC, Dipaola CP, Shaffrey CI, Berven SH, Bilsky MH, Harrop JS, Fehlings MG, Boriani S, Chou D, Schmidt MH, Polly DW, Biagini R, Burch S, Dekutoski MB, Ganju A, Gerszten PC, Gokaslan ZL, Groff MW, Liebsch NJ, Mendel E, Okuno SH, Patel S, Rhines LD, Rose PS, Sciubba DM, Sundaresan N, Tomita K, Varga PP, et al.: Spinal instability neoplastic score: an analysis of reliability and validity from the spine oncology study group. J Clin Oncol 2011, 29:3072–7.