Proton or Photon RT for Retroperitoneal Sarcomas

This research study is a Phase I clinical trial. Phase I clinical trials test the safety of an investigational intervention. Phase I studies also try to define the appropriate dose of the investigational therapy to use for further studies. "Investigational" means that the intervention is still being studied and that research doctors are trying to find out more about it. Retroperitoneal sarcomas are soft tissue tumors located at the far back of the abdomen. Typically, patients with retroperitoneal sarcomas either have surgery for the removal of their tumors alone, or have their tumors removed, followed by standard radiation therapy, or have pre-operative radiation followed by surgery. When conventional radiation therapy is delivered after surgery, it can damage normal tissue. In this study, you will undergo proton beam radiation therapy or IMRT before undergoing surgery for the removal o