[Rectal cancer: The radiation basis of radiotherapy, target volume].

Since the implementation of preoperative chemoradiotherapy and mesorectal excision, the 5-year rates of locoregional failures in T3-T4 N0-N1 M0 rectal cancer fell from 25-30% thirty years ago to 5-8% nowadays. A critical analysis of the locoregional failures sites and mechanisms, as well as the identification of nodal extension, helps the radiation oncologist to optimize the radiotherapy target definition. The upper limit of the clinical target volume is usually set at the top of the third sacral vertebra. The lateral pelvic nodes should be included when the tumor is located in the distal part of the rectum. The anal sphincter and the levator muscles should be spared when a conservative surgery is planned. In case of abdominoperineal excision, the ischiorectal fossa and the sphincters should be included in the clinical target volume. A confrontation with radiologist and surgeon is mandatory to improve the definition of the target volumes to be treated.