In our institution, we rarely perform post-operative radiation therapy, which is frequently associated with 5-fluorouracil (5-FU)-based chemotherapy and is delivered when the surgical specimen of a good patient selected for exclusive surgery shows risks of local recurrence such as incomplete tumour resection as well as nodal disease involvement. Post-operative radiotherapy has shown the advantage of being selectively delivered in patients at high risk of local recurrence as well as the disadvantage of the increased risk of radiation damage of the small bowel loops which may be fixated to the pelvis as a result of the surgical procedure. The risk of small bowel injury has decreased with the advent of a 3D planning system, dietary care and not exceeding the limit dose of 50-54 Gy. Complications of pelvic radiation therapy are related to the radiation field volume, surgical procedure, overall treatment time, fraction size, radiation energy, total dose and technique . Generally, successful treatment of RC depends on large irradiation fields whose arrangement depends on the loca tion of the primary tumour, surgical procedure (low anterior vs. abdominal perineal resection) and volume of the small bowel. Small bowel radiation induced complications are directly proportional to their volume and may be reduced by using contrast media in defining the radiation fields. Gallagher et al.  determined the volume, distribution and mobility of small bowel in the pelvis by using different techniques. There was a significant average small bowel volume decrease when patients, compared with the supine position, were treated in the prone position with compression of the abdominal wall and distension of the bladder. At our institution we use the prone position and a custom-made belly board for selected patients undergoing post-operative radiation therapy . The knowledge of both local and nodal failure patterns is important for planning radiation therapy fields which should include all potentially contaminated retroperitoneal soft tissue. The majority of local failures in cases of APR occur in the posterior pelvis, presacral space, primary tumour site and perineum. The reported risk areas include the internal iliac, presacral and obturator lymph nodes. After an APR, a wire marker should be used to identify the perineal scar for defining the inferior limit of the beams. When the rectum is resected anteriorly, a Foley catheter is inserted into the rectum and retracted inferiorly in order to identify the anorectal junction and define the inferior limit of the beams. The cranial limit of the field is usually L5-S1 interspace; the lateral borders extend 1.5-2 cm lateral to the widest part of the pelvis bones. Posterior fields include the whole sacrum including a 1-cm posterior margin to allow dose to build up in the presacral area. The anterior border is defined to encompass the internal or internal plus external iliac nodes according to the pathological N stage. When boost doses of radiation are required, the fields are redesigned and 3D treatment planning are performed in order to spare the tissues which are considered not at risk. At present, intensity modulated radiation therapy (IMRT) does not have an established role in postoperative radiation therapy for RC including stages assessed as T3N0N+ and M0R0.
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