Short Course Radiation Treatment for Patients With Primary or Locally Recurrent Retroperitoneal Sarcoma Prior to Surgery

Inclusion Criteria:

• Participants must have a histologically confirmed STS of the retroperitoneal spaceor infra-peritoneal spaces of pelvis

• Participant must have radiologically measurable disease (RECIST 1.1), as confirmedby abdomino-pelvic CT or MRI

• Participant must have primary, locally recurrent, or metastatic disease requiringtreatment of the retroperitoneal mass

• Tumor must be suitable for radiotherapy and surgery based on pre-treatment CTscan/MRI in multidisciplinary discussion with surgeon and radiation oncologist (anticipated macroscopically complete resection, R0/R1 resection)

• Age: 18 years or older

• ECOG performance status ≤2

• Absence of history of bowel obstruction, mesenteric ischemia, or severe chronicinflammatory bowel disease.

• Normal renal function (calculated creatinine clearance ≥50 mL/min)

• Normal bone marrow and hepatic function (white blood cell count ≥2·5 × 10⁹ cells perL, platelet count ≥80 × 10⁹ cells per L, and total bilirubin <2 times upper limit ofnormal)

• Women of child-bearing potential must have a negative pregnancy test within 3 weeksprior to the first day of study treatment

• Patients capable of childbearing/reproductive potential should use adequatecontraception

• Ability to understand and the willingness to sign a written informed consentdocument

Exclusion Criteria:

• Sarcoma originating from bone structure, abdominal or gynecological viscera

• Any of the following histological subtypes: gastrointestinal stromal tumor,rhabdomyosarcoma, primitive neuroectodermal tumor or other small round blue cellsarcoma, osteosarcoma, chondrosarcoma, aggressive fibromatosis, or sarcomatoid ormetastatic carcinoma

• Prior RT to the RPS

• Prior abdominal or pelvic irradiation for other prior malignancy or other disease

• Prior different invasive malignancy may be eligible per the discretion of thetreating investigator and review by the Principal Investigator (PI)

• Prior chemotherapy or immunotherapy within 6 weeks of start of RT

• Pregnant women are excluded from this study because RT has the potential forteratogenic or abortifacient effects.

• HIV-positive individuals on combination antiretroviral therapy are ineligiblebecause of the potential for increased sensitivity to RT