Prostate radiotherapyLarge prostate motion produced by anal contraction
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.
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2013, Radiotherapy and OncologyCitation Excerpt :The resulting simDVHs are therefore (still) only surrogates of the actually delivered DVHs. Actual rectal motion patterns are caused mainly by individual deformations due to variations in organ filling, varying both between patients as well as fractions [2,3,5,24] and may additionally be correlated to the motion patterns of the adjacent organs [25]. In a previous study we have compared accumulated dose distributions, based on re-calculations on repeat CT images following either rigid or deformable image registration, to planned dose distributions.