Clinical Outcomes of Intensity-modulated Carbon-ion Radiotherapy for Bone and Soft Tissue Tumors

Background/Aim: Carbon-ion radiotherapy (CIRT) for bone and soft tissue tumors (BSTs) has been reported to have favorable clinical outcomes. Intensity-modulated CIRT (IMCT) techniques have been developed to further reduce dose delivery to adjacent organs compared to conventional CIRT. We retrospectively analyzed the clinical results of IMCT for BSTs and investigated treatment efficacy and toxicity. Patients and Methods: This study included 9 consecutive BSTs patients who underwent IMCT at the Kanagawa Cancer Center from January 2016 to April 2021. IMCT was administered at a dose of 60.8-70.4 Gy (relative biological effect) in 16 fractions. The time to event was calculated from the initiation of IMCT. Toxicities were evaluated using the Common Terminology Criteria for Adverse Events version 5.0. Results: The median age was 49 (range=16-71) years. The median observation period was 57.6 (range=7.0-77.8) months. There were 7 and 2 cases for IMCT because of proximity to the spinal cord and intestinal tract, respectively. There was one death during the observation period, which occurred 7.0 months after the initiation of treatment. Clinical recurrence occurred in 3 patients at 1.3, 17.8, and 22.4 months after the initiation of treatment, respectively. Acute toxicity of Grade 2 or higher was seen in 2 patients with Grade 2 pharyngeal mucositis. Late toxicities of Grade 2 or higher included 1 case each of Grade 2 neuralgia and peripheral neuropathy, as well as 1 case of Grade 3 fracture. Conclusion: IMCT for BSTs showed good local therapeutic efficacy and tolerable toxicity in patients with bone and soft tissue tumors.