Management of Chordoma With Spinal Stereotactic Radiosurgery (SSRS)

Purpose/objective(s) Chordomas are rare tumors of notochordal origin affecting the skull base, spine, and sacrum. Given their high propensity for local recurrence and chemo/radioresistant biology, current treatment paradigms involve maximally safe en-bloc resection with or without adjuvant radiation therapy (RT). SSRS describes a modern approach to dose escalated RT, most commonly used for spine metastases. We analyzed our large single-institution database to test the hypothesis that SSRS provides comparable oncologic and safety outcomes relative to historical controls. Materials/methods We identified 21 patients with mobile spine or sacral chordoma (25 lesions) treated with SSRS at our institution from 2006 to 2020. We reviewed records to obtain patient, disease, and treatment characteristics, as well as outcome data including survival, local control, and toxicity attributable to SSRS. We performed a Kaplan-Meier analysis to estimate overall survival and local control rates, and a Cox proportional hazard model was used for univariate and multivariate analysis. We also performed a logistic regression to examine risk factors for insufficiency fractures. Significance was defined at a P Results Patients were treated with IMRT in 1,3, or 5 fractions with a simultaneous integrated boost. The median BED2 was 312 Gy (24 Gy/1 fraction to the GTV, 16 Gy to CTV) (Range 120-312 Gy). 44% of lesions were treated in the salvage setting, and 36% were treatments for metastases. All patients had gross disease at the time of SSRS. With median follow-up of 30 months, overall survival (OS) was 95.0%, 89.1%, 48.2% and local control (LC) was 91.5%, 86.9%, and 55.3% at 1, 2, and 5 years respectively. Covariates significantly associated with OS included: performance status, prescribed BED, mobile spine location, non-metastatic site treated, disease limited to 1 site, and GTV Dmin BED2 > 119.28), and the multivariate analysis did not converge. Covariates significantly associated with LC on univariate analysis included: conventional histology, and prescribed BED, while chondroid histology was associated with decreased LC. Only prescribed BED was significant on multivariate analysis. Seven patients were treated with definitive SSRS to their primary site, and there was 1 death (not attributable to RT) and 1 local failure in this group. No radiation myelopathy events were identified. Six patients (29%) required stabilization for sacral or spinal insufficiency after SSRS (median 13 months). No features were identified that significantly predicted for fracture. Conclusion To the best of our knowledge, this series represents over a quarter of all reported spine and sacrum chordoma cases treated with stereotactic radiation in the literature. Our data are comparable to published population-based and single-institution case series, particularly given the prevalence of salvage and metastatic cases in this cohort, and they support the use of SSRS throughout the disease course of spine and sacral chordoma. Author disclosure S. Maroongroge: None. D. Boyce-Fappiano: None. K. Diao: None. B. Amini: None. A.P. Conley: None. J. Li: Research Grant; BMS, Medtronic. Honoraria; Monteris. Travel Expenses; Elekta. D.N. Yeboa: Research Grant; Brockman Foundation, MD Anderson Shirley Stein Award, MD Anderson Cancer Center. member for reviewing abstracts; ASTRO.M. McAleer: Honoraria; PREX S. p. A., AOSpine, Osler Institute. Speaker's Bureau; Osler Institute. Travel Expenses; Osler Institute. C. Tatsui: None. L.D. Rhines: None. A.J. Ghia: None.