Purpose: To evaluate the use of postoperative proton therapy (PT) in extracranial chordoma.
Patients and methods: Twenty-six patients were treated. Gross total resection was achieved in 18 patients. Nine patients had cervical, 2 had thoracic, 8 had lumbar, and 7 had sacro-coccygeal chordomas. Thirteen patients had implants. PT was administered after function-preserving surgery, using a gantry and spot scanning, without or with intensity modulation (IMPT; 6 patients), and/or photon-based radiotherapy (RT, 6 patients). Median total dose was 72 cobalt Gray equivalent (CGE; range, 59.4-74.4), with means of 70.5 and 73.2 CGE for patients with and without implants. Median follow-up time was 35 months (range, 13-73 months). Adverse events were scored using the Common Terminology Criteria for Adverse Events grading system (version 3.0).
Results: At 3 years, actuarial overall survival (OS) and progression-free survival (PFS) rates were 84% and 77%, respectively. One patient each died of local failure (LF), distant failure (DF), suicide, and secondary tumor. We observed 5 LFs and 3 DFs; 3-year LF-free and DF-free survival rates were 86%. We observed four radiation-induced late adverse events (Grade 2 sensory neuropathy; Grade 3 subcutaneous necrosis, and osteonecrosis; and Grade 5 secondary cancer). In univariate analysis, implants were associated with LF (p = 0.034). Gross residual tumor above 30 mL was negatively associated with OS (p = 0.013) and PFS (p = 0.025).
Conclusions: Postoperative PT for extracranial chordomas delivered with spot scanning offers high local control rates. Toxicity was acceptable. Implants were significantly associated with LF. Residual tumor above 30 mL impacted negatively on OS and PFS.