Large prostate motion produced by anal contraction.
ABSTRACT The aim of this study was to define the effects of voluntary anal contraction on prostate motion in an experimental setting.
Thirty-eight patients (median age, 76years) 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.
Mean (±standard deviation, SD) overall displacement of the prostate due to anal contraction was 0.3±1.4mm to the right, 9.3±7.8mm to the anterior, and 5±4mm to the cranial direction. Mean displacement of the pelvis was 0.5±1.8mm to the right, 4.1±7.1mm to the anterior, and 1±3mm to the cranial direction. Mean displacement of the prostate relative to the pelvis was 0.1±1.1mm to the left, 5.2±3.3mm to the anterior, and 4±4mm to the cranial direction.
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.