By Matt Susko, MD, MS, University of California San Francisco
Three studies presented at ASTRO 2026 in Boston are advancing the field's understanding of vertebral compression fracture (VCF), a consequential potential side effect from stereotactic body radiation therapy (SBRT) of spinal metastases. Taken as a set, the research validates tools for identifying which patients are most at risk, refines the dosimetric thresholds that underlie the risk, and provides preliminary result on the use of cement augmentation as a means to prevent it.
Much of that progress starts with knowing who is at elevated risk of developing a VCF. Brianna Galvin, MD, and colleagues set out to validate a previously developed VCF risk score — based on spinal location, spinal instability score >6 (SINS), and epidural tumor extension — against nearly 1,600 spinal segments from two outside institutions using different fractionation schemes. The model held up well, patients with the highest risk scores saw two-year fracture rates as high as 34% to 64%, compared to roughly 4–9% for the lowest-risk group, with risk climbing consistently as the score increased. This tool now provides robust evidence to guide decisions about which patients are at increased risk for VCF and who may benefit the most from preventive treatment before SBRT is delivered.
Knowing who is at risk is important, however the dosimetric implications of spine SBRT matters as well. A larger multi-institutional analysis, led by Michael LeCompte, MD, MS, and spanned 10 international centers, with more than 2,200 spinal segments treated, sought to refine the dosimetric metrics that are used during treatment planning. Overall fracture rates were relatively low, at 11.7% by three years, and local tumor control remained strong. Notably the analysis found that the dose reaching a large portion of the treatment target, specifically the dose covering 90% of the planning target volume (PTV), was a stronger indicator for fracture risk compared to smaller high-dose hotspots. The researchers identified a minimum dose to 90% of the PTV of 21.3 Gy, 29.1 Gy, and 31.8 Gy in three-fraction treatments that corresponded to 10%, 25%, and 33% fracture risk at three years. Using this evidence to counsel patients at the time of treatment initiation will be valuable for understanding who may benefit most from cement augmentation.
With the development of risk scores and dosimetric thresholds that allow for improved stratification for VCF, the natural next question is whether anything can be done as a method of prevention for patients at high risk. A randomized Phase II trial led by Amol Ghia, MD, tested whether prophylactic cement augmentation in high-risk patients prior to radiosurgery could head off fractures before they develop. In preliminary results from 60 patients, prophylactic cement augmentation did not significantly reduce fracture rates or alter local tumor recurrence when compared to single fraction radiosurgery alone. Ultimately 11% of patients who did not undergo prophylactic cement augmentation required the procedure eventually after a fracture developed, with serious toxicities being uncommon throughout the cohort.
Taken together, the three studies provide additional evidence for predicting who is at increased risk for VCF though evidence for prophylactic strategies remains elusive. As spine SBRT becomes more common practice evidence such as this will help guide improvements in patient care and mitigation of toxicities.
The three abstracts featured, Abstract 357, Abstract 356 and Abstract 355 were presented during SS 47: Spine SBRT: Risk, Safety, and Outcomes, at ASTRO's 68th Annual Meeting.
