Reduction of irradiated small bowel volume with Trendelenburg position in gynecologic pelvic radiotherapy.

The aim of this study was to assess the effect of Trendelenburg position in comparison to prone position on small bowel volume and treatment dose in gynecologic pelvic external beam radiotherapy using three-dimensional conformal treatment plans. Eight patients with gynecologic cancers, treated with definitive or postoperative pelvic radiotherapy were investigated. Pelvic computerized tomography (CT) scans for treatment planning were performed in prone and 25 degree Trendelenburg positions for each patient. The dose-volume histograms of small bowel within the treatment fields were obtained and compared for both positions. The clinical target volume (CTV) and the planning target volume (PTV) were also defined and evaluated in the subjects. Treatment dose was 5040 cGy to PTV with 180 cGy daily fraction doses in both techniques for all patients. The average irradiated small bowel volume was 726 cc for prone position and 458 cc for the Trendelenburg position. The average irradiated small bowel volume reduction in the Trendelenburg position was 38.0% (95% CI 19.5 +/- 38%) compared with the prone position. The average small bowel percent dose was 25.4% (1280 cGy) for Trendelenburg position and 39.9% (2010 cGy) for prone position. PTV doses were similar in both techniques. The results of this dosimetric study suggest that gynecologic pelvic radiotherapy in the Trendelenburg position decreases the volume of irradiated small bowel compared to prone position and may decrease treatment related small bowel morbidity. Clinical benefit of this position should be evaluated in further clinical studies.