Proton Beam Radiation Therapy in Treating Patients With Retroperitoneal Sarcoma

Inclusion Criteria: * Patients with a histologic diagnosis of sarcoma in the peritoneum/retroperitoneum/pelvis are eligible for this study * Patients must have either radiographic(pre-operative) or pathologic (post-operative) evidence of disease limited the peritoneum/retroperitoneum/pelvis without evidence of peritoneal sarcomatosis * For pre-operative cases, the patient must be considered operable/resectable as judged by the attending surgeon (this is determined by an extensive radiographic and medical evaluation that includes but is not limited to: CT Chest and Abdomen with contrast, MRI/CT Brain and Medical/Cardiac Clearance) * Patients should have an EGOC status of 0-2 * Patients must sign a document that indicates that they are aware of the investigative nature of the treatment of this protocol, and the potential benefits and risks (patients unwilling or unable to sign informed consent are excluded from the study) * Women of child-bearing potential as long as she agrees to use a recognized method of birth control (e.g. oral contraceptive, IUD, condoms or other barrier methods etc.); hysterectomy or menopause must be clinically documented Exclusion Criteria: * Prior or simultaneous malignancies within the past two years (other than cutaneous squamous or basal cell carcinoma, melanoma in situ or thyroid carcinoma) * Pregnant women, women planning to become pregnant and women that are nursing * Patients who experience surgical complications that prevent radiation from starting for 5 months or more, unless there is evidence of gross residual disease