DOES LIMITING HOTSPOTS OUTSIDE THE GTV DECREASE THE RISK OF VERTEBRAL COMPRESSION FRACTURE IN PATIENTS BEING TREATED WITH SPINE SBRT? A SINGLE INSTITUTION EXPERIENCE

Abstract

Purpose:

Vertebral compression fracture (VCF) is one of the most common and challenging adverse events following stereotactic body radiation (SBRT) to the spine. Among the many possible predictive factors for VCF, radiation dose per fraction has consistently been found to increase the risk. In response to this, our institution has recently adopted a new constraint to limit dose in the PTV – (GTV+2mm) region to <110% under the hypothesis that limiting the hotspots (HS) outside the GTV will decrease the risk of VCF. This study aims to test this hypothesis and evaluate the effects of this new constraint on VCF rates and local control.

Materials and Methods:

A retrospective review was conducted of all patients treated with SBRT between October 2014 and December 2022 for de novo spinal metastases. Patients with pre- and post-treatment MRIs were selected for the study cohort. Clinical, dosimetric, and survival data were collected, and survival analyses were performed using the Kaplan-Meier method to compare outcomes between plans that respected and exceeded the HS constraint.

Results:

80 patients underwent SBRT treatment to 117 spine segments, 35 of which respected the PTV-(GTV+2mm) HS constraint. The median age was 64 (range: 28-83). At a median follow up of 33 months, 36 patients died. The mean overall survival was 60 months (95% CI: 50-69 months). The cumulative risk of VCF at 24 months was 6% (95% CI: 0-15%) for segments treated with the HS-limiting constraint and 19% (95% CI: 9-28%) for those without (p=0.10). Local control at 24 months was 88% (95% CI: 76%-99%) and 82% (95% CI: 73-91%), respectively (p=0.31).

Conclusions:

Although our small sample size did not show any significant differences, the lower VCF rates observed suggest a potential benefit of applying the PTV – (GTV+2mm) <110% constraint in reducing VCF rates associated with SBRT. Future prospective studies could be performed to further evaluate this.