356 - Normal Tissue Complication Probability of Vertebral Compression Fracture for Stereotactic Body Radiotherapy for Spine Metastases: A Multi-Institutional Study
Presenter(s)
M. C. LeCompte1,2, J. Grimm3, S. Ke4, K. Dibs5, R. Raval5, S. G. Soltys6, M. G. Mendoza6, C. L. Tseng7, A. Sahgal8, S. S. Lo9, J. Tsai10, E. M. Dunne11, A. Bergman11, D. J. Byun12, J. S. Silverman12, M. C. Foote13, N. Gatt13, S. E. Combs14, E. H. Balagamwala15, and K. J. Redmond16; 1Southeast Radiation Oncology Group, Charlotte, NC, 2Levine Cancer Center, Atrium Health, Charlotte, NC, 3Wellstar Health System, Marietta, GA, 4Division of Quantitative Sciences, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, MD, 5Department of Radiation Oncology, James Cancer Hospital/Wexner Medical Center, The Ohio State University, Columbus, OH, 6Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, 7Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 8Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada, 9Department of Radiation Oncology, University of Washington/Fred Hutchinson Cancer Center, Seattle, WA, 10MultiCare Cancer Institute, Tacoma, WA, 11BC Cancer Vancouver, Vancouver, BC, Canada, 12Department of Radiation Oncology, NYU Grossman School of Medicine, New York, NY, 13Department of Radiation Oncology, University of Queensland, Brisbane, QLD, Australia, 14Department of Radiation Oncology, Technical University Munich, Munich, Germany, 15Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH, 16Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, Baltimore, MD
Purpose/Objective(s):
Stereotactic body radiotherapy (SBRT) for spine metastases affords excellent local control but may be associated with a dose-dependent risk of treatment induced vertebral compression fracture (VCF). Yet, dosimetric objectives to minimize VCF risk remain uncertain. We present a detailed dose-volume analysis of VCF risk following spine SBRT in a multi-institutional cohort.Materials/Methods:
Patients with spine metastases treated with SBRT at 10 international institutions between 2009 – 2024 were retrospectively reviewed. Those with prior surgical stabilization or radiation to the same site as SBRT were excluded. VCF was defined as new development or worsening of existing vertebral body height loss not attributable to tumor growth. Analyses were completed at the lesion level. Individual dose volume histograms (DVH) were tabulated for subset analysis. DVH availability varied by treatment era and institution. All fractionation schemes were converted to 3-fraction equivalent dose (3fxED) using the linear quadratic model with an a/ß of 3 Gy. Dose-time normal tissue complication probability (NTCP) models were constructed by stratifying data into four dose groups using a k-medians clustering algorithm then performing time-to-event analysis to estimate overall 3-year VCF risk. In 3fxED, bin edges were 10.9 Gy (min), 20.8 Gy, 25.7 Gy, 28.8 Gy, and 37.1 Gy (max).Results:
1,659 lesions were analyzed representing 2,203 spinal segments among 1,290 patients. Most were treated in 3 fractions (n = 531, 32.0%). The median prescription doses for 1-, 2-, 3-, and 5-fraction regimens were 18 Gy, 24 Gy, 27 Gy, and 30 Gy, respectively. Common histologies were prostate (16.4%), non-small cell lung cancer (15.3%), and kidney/renal cell carcinoma (15.3%). With median follow up of 38.9 mo (95% CI 35.8 – 40.5), local failure was 17.7% at 3 years (95% CI 15.7 – 19.7%). A total of 236 post-SBRT VCF events were reported, with a 3-year cumulative incidence of 11.7% (95% CI 10.1 – 13.4%). Multivariate logistic regression identified total SINS score (0-6 [reference]; 7-12 [OR 1.89, 95% CI 1.33 – 2.70, p<0.001]; 13-18 [OR 5.03, 95% CI 1.81 – 13.94, p = 0.002) and inclusion of the vertebral body in the planning target volume (PTV) (OR 2.58, 95% CI 1.27 – 5.23, p = 0.009) to be predictive for post-SBRT VCF. DVH data were available for 915 lesions. NTCP modeling suggested a steep response of VCF risk to the minimum dose that 90% of the PTV received (PTV D90%) (p = 0.053). In 3 fractions, PTV D90% of 21.3 Gy, 29.1 Gy, and 31.8 Gy corresponded with a 10%, 25%, and 33% risk of VCF at 3 years, respectively.Conclusion:
SBRT for de novo spine metastases offers durable local control, and the rate of post-SBRT VCF was low in this large international cohort. NTCP modeling suggests that doses to large subvolumes (PTV D90%) of the spine contributes more to VCF risk than high doses to smaller regions.