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
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.