A Feasibility Study of Spacer Placement to Avoid the Bowel Radiation Exposure in Carbon Ion Radiotherapy for the Treatment of Retroperitoneal/Pelvic Tumors

Interventions: To keep the bowel away from the radiation field, the adipose tissue in the abdominal cavity or superimposed Gore-Tex sheets will be placed onto the tumor as a spacer. Primary outcome(s): Intraoperative and postoperative morbidity rate Study Design: Single arm Non-randomized