2607 - Outcomes Associated with Proton Spine Stereotactic Body Radiation Therapy

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, D. S. Higginson¹, J. Haseltine², B. A. Mueller², A. Schmitt¹, M. Vaynrub¹, W. C. Newman¹, E. Lis¹, O. Barzilai¹, M. Bilsky¹, and Y. Yamada²; ¹Memorial Sloan Kettering Cancer Center, New York, NY, ²Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY

Purpose/Objective(s): Little is known about the long-term outcomes of patients with spinal metastases treated with proton stereotactic body radiation therapy (pSBRT), particularly in the setting of re-irradiation (reRT).

Materials/Methods: This is a retrospective cohort study of patients with spinal metastases treated between 2015-2023 utilizing hypofractionated (=10 fractions) radiotherapy (HFRT) with protons. All patients received follow-up magnetic resonance imaging at least 1 month after treatment. Outcomes of interest included local control (LC), defined radiographically, as well as long-term toxicities.

Results: A total of 51 patients treated to 57 lesions met inclusion criteria. Median follow-up after RT was 14 months (interquartile range [IQR] 7-19), and the median overall survival after RT was 7.2 months (95% confidence interval [CI] 4.1-15.5 months). The most common dose-fractionation scheme was 40 Gy in 5 fractions (n=46, 81%). The median biological effective dose assuming an a/ß of 10 was 72 Gy (range 45-72 Gy). Other dose-fractionation regimens included 27 Gy in 3 fractions (n=3, 5.3%) and 36 Gy in 6 fractions (n=3, 5.3%). There were 11 cases of first time SBRT utilizing protons (19%), whereas 23 courses (40%) were second-time reRT, 19 courses (33%) were third-time reRT and 4 courses (7%) were fourth-time reRT. Median cumulative equivalent dose in 2-Gy fractions (EQD2) was 113 Gy (IQR 83-153). The 1-year LC rate was 89% (95% CI 80-95.7%). There were 5 grade (G) 3 toxicities (9%), including 1 instance of radiation myelitis, 1 tracheoesophageal fistula, 1 esophageal stricture, 1 instance of wound dehiscence, and 1 instance of bowel necrosis. All G3 toxicities occurred in patients who received 3-4 overlapping courses of RT.

Conclusion: PSBRT is associated with excellent local control in this large cohort of heavily re-irradiated patients (81% reRT). G3 toxicities were limited to patients who received 3-4 overlapping courses of RT.