The variation of small bowel volume within the pelvis before and during adjuvant radiation for rectal cancer.

Prior to adjuvant postoperative radiation therapy for carcinoma of the rectum, 21 consecutive patients had small bowel barium studies to determine whether there was an optimal interval between ingestion of barium sulphate and imaging, and whether the volume of small bowel within the posterior pelvis was constant throughout the course of treatment. It was found that the optimum interval prior to imaging after ingestion of barium was 1.5-2 h. For seven patients there was no, or minimal, small bowel visualised within the posterior pelvis at any time. For six patients there was an apparently fixed loop of bowel within the posterior pelvis at simulation, both before and during treatment. For a further eight, the small bowel was mobile and the volume of bowel within the posterior pelvis was reduced by bladder distension. Seven of these eight patients had repeat studies during the course of treatment and in five the difference between the appearance of the small bowel with the bladder full and empty was lost. It is concluded that the displacement of small bowel from the posterior pelvis by bladder distension may not be reliably maintained throughout a course of pelvic radiation.