Outcomes of Patients With Primary Sacral Chordoma Treated With Definitive Proton Beam Therapy

To evaluate the efficacy and safety of definitive proton beam therapy (PBT) for primary sacral chordoma.

We conducted a retrospective analysis of the clinical outcomes of eligible patients with primary sacral chordoma who had undergone definitive PBT with 70.4 Gy (relative biological effectiveness) in 32 fractions at our institution from September 2009 to October 2015. Local progression-free survival, distant metastasis-free survival, disease-free survival, cause-specific survival, and overall survival were evaluated. To explore the factors that influenced local progression, the following parameters were analyzed: sex, the presence of a spacer (Gore-Tex sheets), gross tumor volume, and extent of cranial tumor extension. Adverse events were evaluated using the Common Terminology Criteria for Adverse Events, version 4.0. To assess the impact of PBT on pain relief, the change in pain grades was investigated between the initiation of PBT and the last follow-up visit.

Thirty-three eligible patients were analyzed. The median follow-up period was 37 months. The 3-year estimated local progression-free survival, distant metastasis-free survival, disease-free survival, cause-specific survival, and overall survival rates were 89.6%, 88.2%, 81.9%, 95.7%, and 92.7%, respectively. No significant association was between the patients' clinicopathologic characteristics and local progression-free survival. Four patients developed grade 3 adverse events, including acute dermatitis (n = 1), ileus (n = 1), and pain due to sacral insufficiency fractures (n = 2). The pain grades had improved, were unchanged, or had deteriorated in 15, 7, and 11 patients, respectively.

Definitive PBT with 70.4 Gy (relative biological effectiveness) in 32 fractions is an effective treatment with acceptable toxicity for primary sacral chordoma and has the potential to reduce pain.