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PQA 01 - Gastrointestinal Cancer and Central Nervous System
2083 - Modeling Pre-Operative Spine Stereotactic Body Radiation Therapy (SBRT) for Treatment of Metastatic Spinal Disease Requiring Spinal Decompression Surgery
Julia Hall, BA - Loyola University Chicago Stritch School of Medicine, Maywood, IL
J. R. Hall1, T. Botticello2, S. S. Neibart3, R. Garg4, A. M. Schwartz2, L. Vanbenthuysen2, M. J. Khandekar2, K. S. Oh2, H. A. Shih2, W. Small Jr5, J. A. Hirsch4, P. J. Saylor6, M. R. Bussiere2, D. G. Tobert7, G. M. Shankar8, and A. E. Marciscano2; 1Stritch School of Medicine, Loyola University Chicago, Maywood, IL, 2Department of Radiation Oncology, Mass General Brigham / Massachusetts General Hospital, Boston, MA, 3Harvard Radiation Oncology Program, Boston, MA, 4Department of Radiology, Mass General Brigham / Massachusetts General Hospital, Boston, MA, 5Department of Radiation Oncology, Stritch School of Medicine, Cardinal Bernardin Cancer Center, Loyola University Chicago, Maywood, IL, 6Department of Medicine, Mass General Brigham / Massachusetts General Hospital, Boston, MA, 7Department of Orthopaedic Surgery, Mass General Brigham / Massachusetts General Hospital, Boston, MA, 8Department of Neurosurgery, Mass General Brigham / Massachusetts General Hospital, Boston, MA
Purpose/Objective(s): Spine SBRT is an emerging standard for intact and post-op spinal metastatic disease. The post-op paradigm has unique challenges with clinical delays in resuming systemic treatment due to surgical healing and difficulty with target delineation due to hardware imaging artifacts – pre-op spine SBRT may help circumvent these obstacles. We hypothesize that pre-operative spine SBRT offers a dosimetrically non-inferior alternative to post-op SBRT with several clinical and patient-centric advantages. Materials/Methods: An institutional retrospective IRB-approved database of patients treated with post-op spine SBRT between 5/2024–6/2025 identified 10 eligible patients. Medical records were reviewed with attention to SINS, ESCC/Bilsky grade and clinico-radiographic data. A diagnostic CT obtained prior to surgery was a surrogate for a pre-op CT sim. Standard post-op sim and MR/CT myelogram workflows were used. In silico pre/post-op SBRT dyad cases were planned per CCTG SC.24/TROG 17.06 guidelines, prescribing 24Gy/2Fx (permitting GTV SIB to 28Gy). A 1.5mm margin was applied to generate planning risk volume (PRV) – SpinalCord_PRV1.5mm and Equivalent Uniform Dose (EUD a=8) was computed. Descriptive statistics and Wilcoxon matched-pair signed-rank test were used for comparative analysis; p < 0.05 considered significant. Results: In the post-op cohort (n=10), median age was 62.5 yrs, median pre-op KPS=70 and 70% were female. Baseline SINS=10 (8-13), 70% of lesions were in the thoracic spine and 70% were class B per MSK radiosensitivity classifier. Median time from surgery-to-SBRT and surgery-to-systemic treatment was 4.2 weeks and 6.1 weeks. Median pre vs post ESCC grade was 2 (0-3) vs 1c (1a-2) with improved ESCC grade in 60%. During the peri-op window, 50% had progression in non-target spinal disease and 60% had progression in extra-spinal disease. Among 10 dyad cases that modeled pre vs post-op spine SBRT, coverage of GTV/PTV by Rx dose was 93.6/91.7% vs 94.4/90.2% (p=0.63/0.19). GTV Dmax and mean dose to GTV/PTV were 29.4Gy vs 29.6Gy (p=0.44) and 26.6/25.9Gy vs 26.7/25.9Gy (p=0.63/0.44), respectively. GTV Dmin/D98/D95 for pre vs post was 14.0/19.8/23.0Gy vs 15.2/21.0/23.4 Gy (p=0.81/0.63/0.81) with reduced coverage at the epidural GTV - SpinalCordPRV interface. Pre-op GTV/CTV were smaller than post-op volumes – 40.5/59.1cc vs 54.3/110cc (p=0.06). OAR metrics were achieved in all cases with pre vs post SpinalCord_PRV1.5mm EUD of 12.6Gy vs 13.1Gy. Conclusion: Pre-op spine SBRT is dosimetrically feasible achieving acceptable target coverage and OAR sparing, comparable to paired post-op cases. Attention to the GTV-cord interface and surgical pre-planning to identify high-risk epidural areas may guide optimal decompression. Pre-op spine SBRT is an emerging paradigm for a subset of patients that require surgery and may facilitate safe/efficient locoregional treatment of metastatic spinal disease in a patient-centric workflow that minimizes delays to systemic treatment.
