219. Daily MVCTs for assessing the bowel motion and probability distribution maps during pelvic tomoterapy

Purpose To assess inter-fraction bowel loops (BL) motion and quantify its impact on BL DVHs in prostate radiotherapy including pelvic nodes irradiation. Methods Ten patients treated by Helical Tomotherapy, with adjuvant (5) or radical (5) intent, delivering 52.5/51.8 Gy to pelvic-nodes in 30/28 fractions respectively, were enrolled. For each patient, BL contours were drawn on fifteen daily MVCTs, using a validated method for segmentation: BL...