Introduction
Radiotherapy (RT) for bladder cancer patients is performed in multiple “fractions”, i.e., on multiple days. The RT treatment plan is created based on a so-called planning CT, which represents the anatomy of that moment. During treatment, the anatomy may change, among others due to changes in bladder filling. During treatment, this variation is accounted for by using large margins around the target area. As a result, large volumes of healthy tissue are irradiated. The aim of modern RT techniques is to shrink treatment margins, in order to reduce complication risks, while at the same time increase radiation dose to increase the chance of disease-free survival. For this we want to quantify the exact deformation of the urinary bladder and the displacements of the tumor.
Our group developed a finite element model (FEM) of the bladder and surrounding tissues in Abaqus, based on MRI images of a filling bladder [1,2]. The different tissues are modeled with a linear elastic isotropic material model (with values for the parameters E and v from literature). A small step in bladder filling is represented by an arbitrary increase in pressure, and this is scaled to obtain the correct bladder volume. Most likely, this model does not represent realistic pressures or bladder wall stress. However, it represents the deformation of the bladder wall with a reasonable accuracy.
Project
Before this model can be used in the clinical RT practice, multiple improvements are needed:
- Addition of contact elements at the organ boundaries
- Better (non-linear, anisotropic) material models
- Mesh generation based on CT images of bladder cancer patients instead of MR images of healthy volunteers
- Addition of tumor tissue with appropriate material properties
- Validation of the model using an experimental phantom (to be developed) or using filling experiments on porcine bladders (a currently running Master’s thesis research project)
The specifics of the project as well as specific research questions will be determined in discussion with the student.
Your background
We are looking for students with a background in Physics, Engineering or Mathematics, but preferably Biomedical Engineering or similar, with basic knowledge of (or experience in) finite element modeling and (bio)mechanics. Experience with the FEM software package Abaqus is preferable.
More information
This project will be performed at the department of Radiation Oncology at the Academic Medical Center (AMC) in Amsterdam. For more information on this project, please contact Dr. Silvia Wognum at s.wognum@amc.uva.nl.
References
- X. Chai, H. M. van, J. B. van de Kamer, M. C. Hulshof, P. Remeijer, H. T. Lotz, and A. Bel, "Finite element based bladder modeling for image-guided radiotherapy of bladder cancer", Med.Phys. 38(1), 142-150, (2011)
- X. Chai, H. M. van, M. C. Hulshof, and A. Bel, "A voxel-based finite element model for the prediction of bladder deformation", Med.Phys. 39(1), 55, (2012)
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