Outcome and Toxicity of Carbon Ion Radiotherapy for Axial Bone and Soft Tissue Sarcomas

Definitive radiotherapy for bone and soft tissues sarcomas benefits patients deemed unfit for surgery; poor outcomes have been reported with conventional photons, while interesting preliminary results have been described with particle in single-Institution experiences. The aim of the study was to retrospectively evaluate preliminary results of carbon ion radiotherapy (CIRT) in patients with axial bone and soft tissue sarcomas (BSTS) treated with curative intent at the National Center for Oncological Hadrontherapy (CNAO).

From January 2013 to September 2018, 54 patients with axial BSTS were treated with CIRT at CNAO. Their median age was 50 years (range=19-79 years), males/females=1.4:1. Tumor site was the pelvis in 50% of cases (n=27), thoracic region in 24% (n=13), cervical spine in 15% (n=8) and lumbar in 11% (n=6). A total of 76% (n=41) of patients had primary disease, while 24% (n=13) had recurrent disease. Before CIRT, surgery was performed in 47% of cases, including positive margins (R1) in 8 patients, and macroscopic residual disease (R2) in 17. Histological subtypes were mainly represented by chondrosarcomas in 39% (n=21) of patients and osteosarcomas in 24% (n=13). Pre-treatment chemotherapy was administered in 40% of cases (n=22); no patient received previous radiotherapy. All treatments were performed with active scanning CIRT for a median total dose of 73.6 Gy (range=70.4-76.8 Gy), in 16 fractions (4 fractions per week).

Median follow-up was 24 months (range=4-61 months). Four patients were lost to follow-up. Acute toxicities were mild, no >G2 event was reported and no treatment interruption was required. For late toxicity, only G3 neuropathy was detected in 4% of cases (n=2). With a median time to local progression of 13 months (3-35), 15 local failures were observed, resulting in 2- and 3-year local control rates of 67.4% for both. Distant progression occurred in 12 patients, with 1-year progression-free survival (PFS) rate of 97.5%; 2- and 3-year rates were 92.2%. Fifteen patients died resulting in 1- 2- and 3-years overall survival (OS) rates of 87.1%, 75.4% and 64%, respectively. At log-rank test, gross total volume (GTV) >1,000 ml was found to be predictive of local failure (p=0.04), pre-treatment chemotherapy was found to be significantly related to PFS and OS (p=0.02 and p=0.016); also, recurrent disease and distant progression were significantly related to OS (p=0.019 and p=0.0013). Cox proportional-hazards model confirmed that GTV >1,000 ml was related to worse local control (p=0.0010).

CIRT for axial BSTS resulted in mild toxicity, showing promising results in terms of clinical outcomes. A longer follow-up is warranted.