First-in-human phase I study of a non-woven fabric bioabsorbable spacer for particle therapy： Space-making particle therapy (SMPT)

Abstract Background Surgical spacer placement (SSP) is useful in particle therapy (PT) for patients with abdominal or pelvic tumors located adjacent to normal organs. We developed a non-woven fabric bioabsorbable spacer made of polyglycolic acid sutures that degrades via hydrolysis. We then conducted this first-in-human phase I study of the combination of SSP and PT using the PGA spacer and we termed space-making particle therapy (SMPT). This study aimed to evaluate the safety and efficacy of SMPT in patients with unresectable malignant tumor located adjacent to normal organs.. Methods The eligibility criteria included histologically proven malignant abdominal or pelvic tumor adjacent to the intestines, no metastasis, and no previous radiotherapy. Periodic computed tomography (CT) images were obtained before SSP and before, during, and after PT until the spacer disappeared. Treatment planning was performed for each CT image set until the end of PT, and doses for the planning target volume (PTV) and organs at risk were analyzed. The thickness and volume of the PGA spacer were measured in each CT image set. Adverse events were evaluated according to the Common Terminology Criteria for Adverse Events v4.0. Results Five patients were enrolled in this study. All patients received 70.4 Gy (RBE) of irradiation. V 95% of the PTV before SSP, at the beginning of PT, and at the end of PT was 82.1±11.3%, 98.1±1.1%, and 97.1±0.8%, respectively. The PGA spacers maintained enough thickness (≥ 1 cm) until the end of PT and disappeared within 8 months after SSP in all patients. No grade ≥3 acute adverse events were observed. Conclusions The SMPT is feasible and useful for abdominal or pelvic tumors adjacent to the intestines. This method may be applicable to unresectable tumors located adjacent to normal organs and may expand the indications of particle therapy.