Evaluating the effect of rectal distension and rectal movement on prostategland position using cine MRI

Purpose: To evaluate the dynamic interrelationship between rectal distensio n and rectal movements, and to determine the effect of rectal movement on t he position of the prostatic gland using cine magnetic resonance imaging (M RI). Methods and Materials: Fifty-five patients with biopsy-proven or suspected prostate cancer were examined in the axial plane using repeated spoiled gra dient-echo sequences every 10 seconds for 7 minutes. Twenty-four patients r eceived bowel relaxants before imaging. Images were analyzed for the degree of rectal distension, for the incidence, magnitude, and number of rectal a nd prostate movements. Results: Rectal movements were seen in 28 (51%) patients overall, in 10 (42 %) of those receiving bowel relaxants and in 18 (58%) not receiving bowel r elaxants. The incidence of rectal movements correlated with the degree of r ectal distension (p = 0.0005), but the magnitude of rectal movements did no t correlate with the degree of rectal distension. Eighty-six rectal movemen ts resulting in 33 anterior-posterior (AP) prostate movements were seen. Th e magnitude of rectal movements correlated well with degree of prostate mov ements (p < 0.001). Prostate movements in the AP direction were seen in 16 (29%) patients, and in 9 (16%) patients the movement was greater than 5 mm. The median prostate AP displacement was anterior by 4.2 (-5 to +14 mm). Conclusions: Cine MRI is able to demonstrate near real time rectal and asso ciated prostate movements. Rectal movements are related to rectal distensio n and result in significant displacements of the prostate gland over a time period similar to that used for daily fractionated radiotherapy treatments . Delivery of radiotherapy needs to take into account these organ movements . (C) 1999 Elsevier Science Inc.