In an attempt to have better targeting of the prostate during radiotherapy it is necessary to understand the mechanical interactions between bladder, rectum, and prostate and estimate their consequences on prostate motion. For this, the volumes of bladder, rectum, and lungs were modified concomitantly on a deceased person. A CT acquisition was performed for each of these different pelvic configurations (36 acquisitions). An increase in the volume of the bladder or lungs induces a compression of tissues of the pelvic area from its supero-anterior (S-A) to infero-posterior (I-P) side. Conversely, an increase of rectum volume induces a compression from the I-P to the S-A side of the pelvic region. These compressive actions can be added or subtracted from each other, depending on their amplitudes and directions. Prostate motion occurs when a movement of the rectum is observed (this movement depends, itself, on lungs and bladder volume). The maximum movement of prostate is considering maximal bladder or rectal action, and considering maximum lung action. In some other cases, opposition of compressive effects can lead to stasis of the prostate. Based on the volumes of bladder, rectum, and lungs, it is possible to qualitatively estimate the movement of organs of the pelvic area. The best way to reduce prostate movement is to recommend the patient to have an empty rectum, with either full bladder and/or full lungs.
This work was supported by a grant from the French Department of National Education. The authors wish to express their gratitude to: Dr. Caroline Rambaud, forensic pathologist, M.D., Ph.D., hospital Raymond Poincaré, (Garches, France) for her help concerning the preparation of the study, Loic Carpier, data-processing engineer, for his helpful assistance in the implementation of the data analysis software, and Olivia Hammond and Richard Keros for their help in the correction of English.
II. MATERIALS AND METHODS
II.A. Problems due to muscular elasticity of a deceased person
II.B. Patient in supine position
II.C. Filling conditions
II.C.1. Previous considerations
II.C.2. Bladder fillings
II.C.3. Rectal fillings
II.C.4. Lung fillings
II.D. CT acquisition
II.E. Delineation of organs (bladder, prostate, rectum)
II.F. Implementation of software analysis of results
II.G. Organ movement analysis considering position of adjacent organs: Consequences on prostate motion
III.A. Analysis of rectum movements in relation to the position of adjacent organs
III.A.1. With empty lungs
III.A.2. With full lungs
III.B. Analysis of bladder movements in relation to the position of adjacent organs
III.B.1. With empty lungs
III.B.2. With full lungs
III.C. Consequences of these interactions on target prostate volume
III.C.1. Effect of the bladder (for which maximum prostate movement is observed: Configuration transition from B0-R100-L0 to B100-R100-L0; Fig. 7)
III.C.2. Effect of the lungs (for which maximum prostate movement is observed: Configuration transition from B0-R100-L0 to B0-R100-L100; Fig. 8)
III.C.3. Effect of the rectum (for which maximum prostate movement is observed: Configuration transition from B0-R0-L0 to B0-R100-L0; Fig. 9)
III.C.4. Effect of rectum in opposition to that of bladder (for which small movement of the prostate is observed: Transition from B0-R0-L0 to B100-R100-L0 pelvic configuration)
III.C.5. Effect of rectum in opposition to that of lungs (for which small movement of the prostate is observed: Transition from B0-R0-L0 to B0-R100-L100 pelvic configuration)
III.C.6. Global effect on prostate volume
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