Reirradiation With Three-Fraction Stereotactic Body Radiation Therapy for Spinal Metastases

We sought to characterize outcomes from a large institutional database of patients treated with 3-fraction spine stereotactic body radiation therapy (SBRT) after prior overlapping radiation therapy.

The primary outcome of interest was local failure (LF) in the treated lesion, defined based on magnetic resonance imaging. We also characterized toxicities such as vertebral compression fracture and radiation myelitis.

There were 83 patients treated to 87 spinal lesions between 2014 and 2023. Median follow-up was 14.2 (IQR, 6-29.4) months, and median overall survival was 20.5 (95% CI, 16.5-29.9) months. Most lesions were treated with 27 Gy in 3 fractions (n = 78; 90%). Most lesions had been treated with prior conventionally fractionated radiation therapy (59%), and the most common histology was prostate cancer (n = 15; 17%). The 1- and 2-year LF rate was 8.4% (95% CI, 3.7%-16%) and 15% (95% CI, 8.1%-24%), respectively. On univariable analysis, lower minimum dose to the planning target volume (hazard ratio, 0.85, 95% CI, 0.74-0.99, P = .03) and colorectal, cholangio-, or hepatocellular carcinoma histology (hazard ratio 5.6, 95% CI, 1.11-28.4, P = .037) were associated with risk of LF. There was 1 case of radiation myelitis (1.3%) and 5 cases (5.5%) of vertebral compression fracture.

Reirradiation with spine SBRT in 3 fractions appears safe and is associated with a 2-year local control rate of 85%. Lower planning target volume, lower minimum dose, and gastrointestinal histology were associated with increased risk of LF. Further work is needed to identify the optimal dose-fractionation regimen for reirradiation with spine SBRT.