Radiation Therapy for Colorectal Cancer Hee Chul Park, Doo Ho Choi Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. dohochoi@skku.edu Abstract Treatment for high-risk colorectal cancer has evolved from surgical resection alone to the selective use of multimodalities such as chemotherapy and radiation therapy (RT). Postoperative RT can eradicate microscopic disease after surgical resection and preoperative RT leads to decreased tumor burden before the commencement of operation. The role of RT in the management of colon cancer is not confirmatory as of now. While there is some suspicion, no critical evidence can be found. However, some retrospective data support the role of RT to improve the prognosis in patients with colon cancer. Postoperative RT combined with chemotherapy can reduce the locoregional recurrences and exert a critical influence on patients' quality of life. Preoperative RT alone or the combination with chemotherapy down-stages the tumor to decrease the operative morbidity, and promotes the sphincter preservation. Preoperative RT improves local control. In addition, down-staging after neoadjuvant treatment merits attention as prognosticator. Patients who have had better tumor response also had superior survival profile. Treatment approach to locally advanced rectal cancer is changing from postoperative adjuvant one to aggressive application of preoperative modality. Future research efforts will focus the optimal treatment strategies to fortify the complete or near complete response rates. The recent advances in RT technology are also being examined to see whether the tumor response can be enhanced while decreasing toxicity so that more intensive chemotherapy regimens can be combined with RT. This review will trace the evolution of multimodality approach to locally advanced colorectal cancer. Key Words: Colon cancer, Rectal cancer, Radiation therapy