Inclusion Criteria:

- written informed consent

- histologically confirmed, primary or locally recurrent soft tissue sarcoma of the
retroperitoneal space

- judged as at least marginally resectable

- absence of distant metastases

- tumor size ≥ 5 cm

Exclusion Criteria:

- missing written informed consent

- missing histological confirmation of soft tissue sarcoma

- Desmoid tumor (syn. aggressive fibromatosis)

- judged as gross incomplete or not resectable

- incomplete staging

- presence of distant metastases

- prior radiation therapy to the abdominal region

- participation in another clinical interventional study

- inflammatory bowel disease