From August 2019 to August 2020, we inserted
polyglycolic acid (
PGA) spacers and administered
carbon ion radiotherapy (CIRT) to three cases of retroperitoneal
sarcoma at our hospital. We aimed to investigate its utility and safety for retroperitoneal
sarcoma. We analyzed changes in
PGA spacer volume and corresponding computed tomography (CT) values in addition to the dose distribution using in-room CT images that were obtained during treatment. We assessed adverse events and investigated the suitability, safety and effectivity of
PGA spacer insertion. During treatment, changes in
PGA spacer volumes and CT values were confirmed. Volumes increased in patients with a folded
PGA spacer, and it increased 1.6-fold by the end of irradiation compared with planning CT. The CT values decreased by 20-50 Hounsfield units at the end of irradiation compared to the planning CT. Dose distribution evaluation showed that the dose to the gastrointestinal tract adjacent to the
tumor was maintained below the tolerable dose, and a sufficient dose was delivered to the target by
PGA spacer insertion. One case of subileus caused during abdominal surgery for
PGA spacer insertion occurred. No other adverse events, such as digestive disorders, were observed. CIRT with
PGA spacer insertion for retroperitoneal
sarcomas is safe and effective. For cases in which there is no option but to perform irradiation using a
PGA spacer, precautionary measures such as verification of dose distributions using CT images are necessary.