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Quantification of local rectal wall displacements by virtual rectum unfolding
Mischa S Hoogeman1, Marcel van Herk, Josien de Bois
1Department of Radiotherapy, The Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital, Plesmanlaan 121, Amsterdam 1066 CX, The Netherlands.
Summary
This study developed a 2D mapping method to quantify rectal shape and position variations during radiotherapy. Results show significant rectal wall displacements, aiding in analyzing treatment complications.
Area of Science:
- Medical Imaging
- Radiation Oncology
- Anatomical Modeling
Background:
- Rectal shape and position variability during radiotherapy can impact treatment accuracy.
- Quantifying these variations is crucial for understanding dose distribution and potential complications.
Purpose of the Study:
- To develop a novel 2D mapping method for projecting rectal surface elements.
- To quantify local shape and position variations of the rectum during radiotherapy.
Main Methods:
- Utilized CT scans from 19 patients undergoing radiotherapy.
- Developed a method to create a central axis and orthogonal cross-sections of the rectum.
- Unfolded rectal walls to create 2D maps, projecting dose or coordinates.
Main Results:
- Largest rectal wall position variations (1 SD=5-7 mm) occurred at the upper anterior, left, and right sides.
- Anterior-posterior and left-right displacements were most pronounced between 40-80% of the central axis.
- Rectal wall displacements correlated with planning CT scan rectum volume (r=0.85 for AP displacements).
Conclusions:
- A method for virtually unfolding the rectum and projecting dose onto a 2D map was successfully developed.
- Quantified significant rectal shape and dose variations, with systematic errors exceeding random variations.
- The spatial dose information is valuable for analyzing rectal complications in radiotherapy.