Large prostate motion produced by anal contraction.

BACKGROUND AND PURPOSE: The aim of this study was to define the effects of voluntary anal contraction on prostate motion in an experimental setting.

MATERIALS AND

METHODS

Thirty-eight patients (median age, 76 years) with prostate cancer underwent thin-slice computed tomography (CT) in the vicinity of the prostate before and after active anal contraction. Three-dimensional displacement of the pelvis and prostate was measured.

RESULTS

Mean (±standard deviation, SD) overall displacement of the prostate due to anal contraction was 0.3±1.4 mm to the right, 9.3±7.8 mm to the anterior, and 5±4 mm to the cranial direction. Mean displacement of the pelvis was 0.5±1.8 mm to the right, 4.1±7.1 mm to the anterior, and 1±3 mm to the cranial direction. Mean displacement of the prostate relative to the pelvis was 0.1±1.1 mm to the left, 5.2±3.3 mm to the anterior, and 4±4 mm to the cranial direction.

CONCLUSIONS

Voluntary anal contraction within an experimental setting induces large prostate and bone motion, mainly in the anterior and cranial directions. The frequency and magnitude of actual anal contractions during radiotherapy for prostate cancer need to be determined.