Prospective Study Evaluating the Treatment Outcomes for Localised Recurrent, Resectable Retroperitoneal Liposarcoma

Inclusion Criteria: 1. Adult age ≥ 18 presenting with first recurrent well-differentiated and/or dedifferentiated liposarcoma of retroperitoneal space or pelvis after previous macroscopically complete resection (R0/R1 resection) 2. No distant metastasis on cross-sectional imaging of chest/abdomen/pelvis (CT and/or MRI) within 1 month to confirm the absence of metastatic disease 3. Previous histologically proven well-differentiated or dedifferentiated liposarcoma histology only 4. Sarcoma not originating from bone or abdominal or gynecological viscera 5. Tumor confirmed to be resectable with likely R0/R1 resection, and all disease must be deemed to be treatable by RT (joint decision by surgeon and radiation oncologist at a sarcoma multidisciplinary team meeting) 6. WHO performance status 0-2 7. American Society of Anaesthesiologist (ASA) score 1-3 8. No prior RT for the retroperitoneal liposarcoma 9. Prior systemic therapy is allowed 10. No concurrent active malignancy (except for low risk skin malignancy, low risk prostate carcinoma, low risk breast carcinoma including in situ disease) 11. Women of childbearing potential must have a negative pregnancy test within 3 weeks prior to the first day of study treatment 12. Patient deemed able to comply with study requirements according to investigator evaluation 13. Signed, IRB-approved written informed consent Exclusion Criteria: 1. Unresectable disease or likely R2 resection as assessed by the multidisciplinary sarcoma team 2. Extent of recurrence where preoperative RT to all visible disease is not deemed to be feasible 3. Contradiction for RT such as history of bowel obstruction or mesenteric ischemia or severe chronic inflammatory bowel disease 4. Myxoid liposarcoma histology 5. Pregnancy