2608 - Re-Irradiation with Three-Fraction Stereotactic Body Radiation Therapy for Spinal Metastases

08:00am - 09:00am PT

Hall F

Screen: 22

POSTER

Presenter(s)

Christopher Jackson, MD, MS - Memorial Sloan Kettering Cancer Center, New York, NY

C. B. Jackson¹, J. Haseltine², B. A. Mueller², A. Schmitt³, M. Vaynrub¹, W. C. Newman¹, E. Lis¹, O. Barzilai¹, M. Bilsky¹, D. S. Higginson¹, and Y. Yamada²; ¹Memorial Sloan Kettering Cancer Center, New York, NY, ²Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, ³Memorial Sloan Kettering, New York, NY

Purpose/Objective(s): In the setting of prior overlapping radiation therapy (RT) for spinal metastases, stereotactic body radiation therapy (SBRT) is a critical form of management to attain local control and minimize risk of toxicity. We sought to characterize outcomes from a large institutional database of patients treated with re-irradiation (reRT) SBRT from 2014-2023.

Materials/Methods: This is a retrospective cohort study of patients with spinal metastases treated with reRT with 3-fraction SBRT. The primary outcome of interest was local failure (LF) in the treated lesion, defined based on MRI. We also characterized toxicities such as vertebral compression fracture (VCF) and radiation myelitis (RM). We used the Fine and Gray model to assess for associations between clinical variables and risk of LF, with death considered a competing risk. A p-value of 0.05 was considered statistically significant.

Results: There were 83 patients treated to 87 spinal lesions included. Median follow-up after SBRT was 14.3 (interquartile range [IQR] 6-29.4) months and median overall survival after SBRT was 20.5 (95% confidence interval [CI] 16.5-29.9) months. Most lesions were treated with 27 Gy in 3 fractions (90%); the remainder were treated with 30 Gy in 3 fractions. Most lesions had been treated with prior conventionally fractionated RT (59%), and the most common histology was prostate cancer (n=15, 21%). The most common prior RT dose-fractionation regimens were 30 Gy in 10 fractions (n=35; 40%) and 24 Gy in 1 fraction (n=13; 15%). The median cumulative equivalent dose in 2 Gy fractions (EQD2) was 79 Gy (IQR 75-86 Gy) between prior and reRT courses. Median time to reRT was 15 months (IQR 7-24). Treatment included separation surgery in 35 cases (40%). The 2-year LF rate was 15% (95% CI 8.1-24%; crude rate 22%, n=19). On univariable analysis, lower minimum dose (DMin) to the planning target volume (PTV) (hazard ratio [HR] 0.85, 95% CI 0.74-0.99, p=0.03) was associated with risk of LF. There was 1 case of RM (1.3%) in a patient previously treated with 30 Gy in 10 fractions, with reRT to 27 Gy in 3 fractions 23 months after the first course of RT. There 5 cases (5.5%) of VCF; 2 patients required percutaneous screw placement for grade 3 VCF, and the remaining instances of VCF were asymptomatic (grade 1). There were no instances of esophageal fistula/perforation, myositis, or lumbosacral plexopathy.

Conclusion: ReRT with 3-fraction spine SBRT is associated with a 2-year local control rate of 85%, with toxicity rates similar to published outcomes associated with first-course spine SBRT. Lower PTV DMin was associated with increased risk of LF. Further work is needed to identify the optimal dose-fractionation regimen for reRT with spine SBRT.