SU-E-J-16: Prostate Bed Motion during Post-Prostatectomy Radiotherapy

Medical Physics
Z XuQ Wu

Abstract

To report the inter-fractional prostate bed motion (PBM) during post-prostatectomy radiotherapy using cone-beam CT (CBCT). The correlations between PBM, anterior rectal wall and posterior bladder wall shifts were also investigated. Seventy CBCT and 8 planning CT scans from 8 patients treated with prostate bed radiotherapy were retrospectively analyzed. For each CBCT-CT pair, two rigid image registrations were performed: one based on surgical clips and the other based on pelvic bony anatomy. Each registration gives a displacement vector. The difference between the two registration displacements represents the PBM. In addition, rectum/bladder contours on CT and CBCT scans were compared to identify the organ wall motion. Shifts of the anterior rectal wall and posterior bladder wall were assessed by averaging the slice-by-slice distances between contours on two image sets, measured along an anterior-posterior line passing through the symphysis pubis. The prostate bed motion in the left-right (LR), anterior-posterior (AP) and superior-inferior (SI) directions was (0.1±0.9)mm, (0.9±1.6)mm, and (-0.4±1.9)mm, respectively. The derived PTV-CTV margin for LR, AP and SI motion was 3mm, 5mm, and 6mm, respectively. Pearson's correlation coe...Continue Reading

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