 The purpose of this study is to see how CT virtual proctoscopy compares to an ultrasound exam of the rectal area in determining the stage of rectal cancer for people recently diagnosed with rectal cancer. This study will also compare tumor volume before and after neoadjuvant therapy using CT virtual proctoscopy, with the ultrasound exam as a comparison. Neoadjuvant therapy consists of chemotherapy and radiation therapy. Neoadjuvant chemoradiation therapy is done before surgery to reduce the size of tumors. 