Intensity Modulated Radiation Therapy (IMRT) for Patients With Rectal Cancer

Inclusion Criteria: * Histologically or cytologically confirmed adenocarcinoma of the rectum * T3 or N+ disease by MRI or endoscopic ultrasound. Metastatic disease is permitted, except for known brain metastases, as long as local treatment with RT and surgery is recommended. * Prior chemotherapy is permitted. For patients who have previously received bevacizumab, the last dose must be greater than 4 weeks prior to initiation of radiation therapy. * 18 years of age or older * Life expectancy of greater than 3 months * ECOG (Eastern Cooperative Oncology Group) Performance Status of 0, 1 or 2 * Normal organ and marrow function as outlined in the protocol * Women of child-bearing potential and men must agree to use of adequate contraception prior to study entry and for the duration of study participation Exclusion Criteria: * Pelvic radiotherapy prior to entering the study or those who have not recovered from adverse events due to agents administered more than 4 weeks earlier * Participants may not be receiving any other investigational agents. Patients may not be receiving any other treatment for their rectal cancer during study participation * Participants with known brain metastases are excluded from this clinical trial because of their poor prognosis and because they often develop progressive neurologic dysfunction that would confound the evaluation of neurologic and other adverse events * History of known radiation sensitivity syndrome * History of inflammatory bowel disease * Active scleroderma or CREST syndrome * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements * Pregnant or nursing women