The study is a randomized, open, prospective phase II study. The aim of the study is to evaluate the safety and feasibility of a hypofractionated, accelerated radiation approach based on the incidence of grade 3-5 NCI Common Terminology Criteria for Adverse Events (NCI-CTC-AE ) toxicity and / or termination of the planned therapy for any reason with neoadjuvant radiation with active beam guidance of the retroperitoneal Sarcomas using protons or carbon ions before a subsequent tumor resection.

With retroperitoneal sarcomas, the patient benefits from neoadjuvant radiotherapy. Due to the special physical properties of particles (protons and C12 carbon ions), in particular the steep lateral dose drop, an improved protection of adjacent risk organs is e.g. Intestine, kidneys, liver etc. during the process of applying radiotherapy is possible.

The primary study objective is to demonstrate the safety and conduct of study treatment and the incidence of Grade 3-5 NCI-CTC-AE toxicity and / or termination of preferred therapy for any reason. Further target parameter is the proportion of applied therapies without the occurance of degree 3-5 NCI-CTC-AE(s).

The patients are randomized 1: 1 into the two arms (carbon ions vs. protons). Patients receive 39 Gy in (SD 3.0 Gy) in 6 fractions per week.

Secondary study objectives are local control (LC), local progression-free survival from the start of therapy (LPFS), disease-free survival (DFS), overall survival (OS) and quality of life (QoL) determined according to the EORTC-Quality of Life Questionaire (QLQ)- C30 questionnaire.

Inclusion Criteria:

• Histologically confirmed retroperitoneal soft-tissue sarcoma which is resectable or marginally resectable
• Karnofsky index of ≥ 70%
• Age from 18 years
• Completed patient information and written consent
• ability to give consent

Exclusion Criteria:

• Stage IV (distant metastases)
• Lymphogenic metastasis
• Metal implants at the level of the sarcoma, which influence the treatment planning
• Previous radiation therapy in the treatment area
• Desmoid tumors, peritoneal sarcomatosis, GIST
• Simultaneous participation in another clinical study that could influence the results of the respective study
• Active medical implants for which there is no license for ion irradiation at the time of treatment (e.g. pacemaker, defibrillator)
• Pregnant women