The risk of colorectal cancer (CRC) is significant among cancer survivors treated with abdominal radiation therapy (RT). Further, CRC is once of the few cancers for which there is effective screening. Although some expert groups recommend early CRC screening for patients with prior abdominal RT, the effectiveness of early screening is unknown. It is also unknown if radiation-induced CRC passes through a "pre-clinical" phase in which precancerous polyps are detectable and treatable prior to becoming invasive cancers. This study will evaluate whether screening will detect pre-invasive colorectal polyps among survivors treated with RT.