Carbon Ion Radiotherapy for Treatment of Sacral Chordomas: An Institutional and International Comparison of Surgical and Conventional Radiotherapy Outcomes

Background: Chordomas are rare tumors that arise from notochordal remnants. Although maximal safe resection is the preferred initial management, radiotherapy is used in the adjuvant setting or primarily in nonsurgical candidates. Carbon ion radiotherapy (CIRT), as an alternative to surgery alone or conventional radiotherapy modalities, has shown promising results to date. Methods: Baseline and tumor-related characteristics from two institutional cohorts were collected for patients diagnosed with sacral chordomas. Univariable logistic regression was performed to evaluate the association between treatment type and oncologic and toxicity outcomes. Overall survival (OS) and progression-free survival were estimated using the Kaplan-Meier method and compared using the Cox proportional hazards model. The National Cancer Database (NCDB) was also queried for sacral chordoma patients and included in OS analyses. Additionally, a comparison of cost between surgery and CIRT therapy was performed. Findings: A total of 919 patients were included in the study. Comparison of the institutional cohort (en bloc resection) to CIRT showed similar oncologic and toxicity outcomes, despite larger tumors in the CIRT group. The CIRT group experienced lower rates of peripheral motor neuropathy (OR: 0.13 [95% CI 0.04-0.40], p<0.001). In a comparison of NCDB to CIRT, significantly higher OS was found for CIRT when compared to margin-positive surgery without adjuvant radiotherapy (p=0.029) and primary photon radiotherapy alone (p<0.001). There was no difference in OS between patients treated with CIRT or proton radiotherapy. Mean total procedure and 2-year costs for CIRT are less than surgery. Interpretation: These findings suggest that CIRT is a safe and effective treatment for older patients with high performance status and sacral chordoma in which surgery in not preferred. Moreover, the use of CIRT might provide additional benefit for patients who undergo margin-positive resection or who are candidates for conventional radiotherapy alone. Funding Statement: None. Declaration of Interests: The authors have no financial or personal relationships or conflicts related to this work to disclose. Ethics Approval Statement: Following Institutional Review Board (IRB) approval at our institution, a retrospective review of hospital records was carried out for all patients diagnosed with chordoma of the sacrum between April 1994 and July 2017.