New radiation approach aims to cut treatment time for rare cancer

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Participants must have a histologically confirmed STS of the retroperitoneal space or infra-peritoneal spaces of pelvis * Participant must have radiologically measurable disease (RECIST 1.1), as confirmed by abdomino-pelvic CT or MRI * Participant must have primary, locally recurrent, or metastatic disease requiring treatment of the retroperitoneal mass * Tumor must be suitable for radiotherapy and surgery based on pre-treatment CT scan/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 chronic inflammatory 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 per L, platelet count ≥80 × 10⁹ cells per L, and total bilirubin \<2 times upper limit of normal) * Women of child-bearing potential must have a negative pregnancy test within 3 weeks prior to the first day of study treatment * Patients capable of childbearing/reproductive potential should use adequate contraception * Ability to understand and the willingness to sign a written informed consent document 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 cell sarcoma, osteosarcoma, chondrosarcoma, aggressive fibromatosis, or sarcomatoid or metastatic 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 the treating 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 for teratogenic or abortifacient effects. * HIV-positive individuals on combination antiretroviral therapy are ineligible because of the potential for increased sensitivity to RT