Particle therapy using carbon ions or protons as a definitive therapy for patients with primary sacral chordoma

Objective: This study retrospectively evaluated the efficacy and toxicity of particle therapy using carbon ions or protons for primary sacral chordomas. Methods: We evaluated 23 patients with primary sacral chordoma treated with carbon ion therapy (CIT) or proton therapy (PT) between July 2005 and June 2011 at the Hyogo Ion Beam Medical Center, Hyogo, Japan. The median patient age was 72 years. 14 patients were treated with 70.4 Gy equivalents (GyE) in 16 fractions and 9 were treated with 70.4 GyE in 32 fractions. CIT was used for 16 patients, and PT was used for 7 patients. Results: The median follow-up period was 38 months. At 3 years, local control (LC), overall survival (OS) and progression-free survival (PFS) for all patients were 94%, 83% and 68%, respectively. The log-rank test revealed that male sex was significantly related to better PFS (p = 0.029). No other factors, including dose fractionation and ion type, were significant for LC, OS or PFS. In nine patients, >= Grade 3 acute dermatitis was observed, and >= Grade 3 late toxicities were observed in nine patients. The 32-fraction protocol reduced severe toxicities in both the acute and late phases compared with the 16-fraction protocol. Conclusion: Particle therapy for patients with sacral chordoma showed favourable LC and OS. Severe toxicities were successfully reduced by modifying the dose fractionation and treatment planning in the later treatment era. Thus, this therapeutic modality should be considered useful and safe. Advances in knowledge: This is the first study including both CIT and PT for sacral chordomas.