Elsevier

Radiotherapy and Oncology

Volume 104, Issue 3, September 2012, Pages 390-394
Radiotherapy and Oncology

Prostate radiotherapy
Large prostate motion produced by anal contraction

https://doi.org/10.1016/j.radonc.2012.04.005Get rights and content

Abstract

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.

Section snippets

Materials

Institutional review board approval was received for this study, and all patients included in the study provided written informed consent prior to participation.

From April 2007 to March 2009, all patients (median age, 76 years; range, 66–85 years) with localized prostate cancer who were scheduled to receive radiotherapy and whose prostates showed focal calcification were selected as subjects. Focal calcifications in the prostate were used to measure prostate motion.

Methods

The 38 patients enrolled in the study were informed as to its concept, methodology, and rationale, and subsequently provided written informed consent. The patients were then given instruction as to how to actively contract the anus. Specifically, they were asked to contract the anus as if they were repressing the passage of bowel gas or loose stool. After patients indicated that they fully understood how to voluntarily contract the anus, CT (Hi-Speed DX/I; GE Yokogawa Medical Systems, Tokyo,

Results

Maximum, mean, SD, and overall vector length of the prostate and the pelvic displacements with voluntary anal contraction are shown in Table 1.

Case examples

An example obtained from a patient with large motion in the internal prostate position due to the voluntary anal contraction is shown in Fig. 1. Rectal and bladder volumes in this case were almost unchanged after anal contraction.

An example from another patient, in whom the voluntary anal contraction caused large motions in the pelvis and internal prostate position, is shown in Fig. 2.

Discussion

The anal levator muscle is one of a pair of muscles of the pelvic diaphragm that stretches across the bottom of the pelvic cavity like a hammock, supporting the pelvic organs. Among the components of the anal levator muscle, a portion of the anterior pubococcygeus muscle is called the levator muscle of the prostate because it inserts into both the prostate and the tendinous center of the perineum. Therefore, voluntary or involuntary anal contraction arouses internal motion of the prostate

Conclusions

The prostate moves largely in an anterior–cranial direction on voluntary anal contraction in an experimental setting even if pelvic motion is controlled. But the real impact of non-voluntary random anal contraction on prostate movement and the relevance of it in relation to the rectal filling need to be determined in future within an appropriate clinical setting.

Conflict of interest statement

None of the authors have a conflict of interest in this work.

References (35)

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