Preoperative Proton Radiotherapy for Retroperitoneal Sarcoma

Inclusion Criteria: * Patients must have histologically-confirmed intermediate or high grade retroperitoneal sarcomas of any histologic subtype. * Primary or recurrent disease isolated to a single intra-abdominal or retroperitoneal region is allowed. * Tumor must be considered potentially completely resectable as defined by cross sectional imaging (no 360o encasement of the superior mesenteric artery, aorta, inferior vena cava, iliac arteries or iliac veins and no extension of tumor into the vertebral column). * At least 2 weeks must have elapsed from any prior surgery or hormonal therapy. Patients must have ≤ grade 1 acute toxicities of any prior treatment with anti-cancer modalities (returned to baseline status as noted before most recent treatment). Patients with persisting, stable chronic toxicities from prior treatment ≤ grade 1 are eligible. * Age ≥18 years at time of consent. * Life expectancy of greater than 3 months. Physician documented. * Women of child-producing potential must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation and the subsequent 6 months. Patients must have a negative serum pregnancy test within 2 weeks prior to beginning treatment on this trial. Sexually active men must also use appropriate contraception method and should not father a child while receiving therapy during this study. * Ability to understand and the willingness to sign a written Institutional Review Board(IRB) stamped study specific informed consent document before undergoing research related procedures or study treatment. * Biopsy is required with pathologic confirmation of intermediate or high grade sarcoma with pathology review at the University of Florida. * Agree to allow their tissue to be used for current study. Exclusion Criteria: * Receiving any investigational agents. * Evidence of metastatic disease. * Uncontrolled intercurrent illness and/or psychiatric illness/social situations that would limit compliance with study requirements. * Pregnant and nursing women are excluded from this study because the radiotherapy may have the potential for teratogenic or abortifacient effects. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with these agents, breastfeeding should be discontinued if the mother is treated. * All herbal and/or alternative medications should be discontinued while on study, including, but not limited to: Hydrastis canadensis (goldenseal), Uncaria tomentosa (cat's claw) or Echinacea angustifolia. * Requirement for treatment with immunosuppressive agents or chronic steroids. * Previous intra-abdominal or retroperitoneal radiotherapy. * Treatment with cytotoxic agents and/or treatment with biologic agents within the 4 weeks prior to beginning treatment on this study.