Treatment planning aids in prostate cancer: Friend or foe?

Background: Rectal barium is commonly used as a treatment planning aid for prostate cancer to delineate the anterior rectal wall. Previous research at the Ottawa Regional Cancer Centre demonstrated that retrograde urethrograp hy results in a systematic shift of the prostate. We postulated that rectal barium could also cause prostate motion. Purpose: The study was designed to evaluate the effects of rectal barium on prostate position. Methods and Materials: Thirty patients with cT1-T3 prostate cancer were eva luated. Three fiducial markers were placed in the prostate. During simulati on, baseline posterior-anterior and lateral films were taken. Repeat films were taken after rectal barium opacification. The prostate position (identi fied by the fiducials) relative to bony landmarks was compared before and a fter rectal barium. Films were analyzed using PIPsPro software. Results: The rectal barium procedure resulted in a significant displacement of the prostate in the anterior and superior direction. The mean displacem ent of the prostate measured on the lateral films was 3.8 mm (SD: 4.4 mm) i n the superior direction and 3.0 min (SD: 3.1) in the anterior direction. Conclusions: Rectal barium opacification results in a systematic shift of t he prostate. This error could result in a geographic miss of the target; th erefore, alternate methods of normal tissue definition should be used. (C) 2001 Elsevier Science Inc.