To study the feasibility of reducing the dose of preoperative radiotherapy in MLS (Myxoid Liposarcomas) from 50 Gy to 36 Gy while maintaining comparable clinicopathological responses.

• A Bayesian approach is considered for the analysis of this trial. The aim is to provide a stopping rule for inefficacy of the new dose.
• Two aspects are important to elucidate the mechanism of this treatment: dynamic investigations of perfusion and vasculature. Apart from participation to the dose reduction paragraphs of this study, patients will be also asked to undergo, at clinically relevant dose points, dynamic contrast enhanced (DEC) MRI scans and separately tumor biopsies.

Inclusion Criteria:

1. Age above or equal to 18 years
2. Biopsy proven MLS (including the reciprocal chromosomal translocation t(12;16)(q13;p11); A the primary sarcoma in case of non-metastatic disease for management is with curative intent (regimen to be chosen = 18 x 2 GY) B in case of oligometastatic patients, the metastasis may also be irradiated to a dose of 36 GY in order to postpone the time interval to next systemic chemotherapy. These patients are usually not operated upon and the total dose may also be reached in 12 times 3 Gy, for convenience purposes (see paragraph 10 for radiobiological considerations).
3. ECOG (Eastern Cooperative Oncology Group) PS (Performance Status) 0-2
4. Patients must be able (physically, mentally and socially) to complete a series of RT, followed by an observation period of 4-6 weeks and undergo surgery.
5. Written informed consent

Exclusion Criteria:

1. Prior radiotherapy to the target area.
2. Anticoagulant medication of any kind; especially Ascal®(and derivates), coumarines (Sintrom® and Marcoumar®), all heparin and heparin-like formulations. (Note: this exclusion criterion only applies for patients consenting to the translational research part of the study; patients on anticoagulant medication as described above may take part in the dose reduction part of the study, but the repeat biopsies may not be taken.)
3. Pregnancy -