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Surface area overestimation within three-dimensional digital images and its consequence for skeletal dosimetry
D A Rajon1, P W Patton, A P Shah
1Department of Nuclear and Radiological Engineering, University of Florida, Gainesville 32611-8300, USA.
Medical Physics
|May 30, 2002
Summary
Monte Carlo simulations for trabecular bone dosimetry overestimate energy absorption due to the surface-area effect. Improving image resolution can compensate for errors in low-energy electron dosimetry, but alternative interface definitions may be more effective.
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Biomedical Imaging
Background:
- Trabecular bone dosimetry often uses Monte Carlo simulations on 3D bone images.
- Previous studies noted an overestimate in absorbed energy fraction for low-energy electrons due to the surface-area effect.
- This effect stems from an inaccurate representation of the bone-marrow interface in digital images.
Purpose of the Study:
- To investigate the surface-area effect in trabecular bone dosimetry using simplified spherical models.
- To quantify the impact of voxelization on bone-marrow interface surface area.
- To assess the influence of image resolution on dosimetry errors for low-energy electrons.
Main Methods:
- Theoretical analysis of voxelized spherical cavities to determine surface area overestimation.
- Creation of single-sphere models simulating marrow cavities with internal and external electron sources.
- Voxelization of models at varying resolutions and performance of Monte Carlo transport calculations.
Main Results:
- Voxelization of spherical cavities leads to a 50% overestimation of surface area, irrespective of voxel size.
- This surface area overestimation can result in a 50% overestimate of the cross-absorbed fraction for electrons below 100 keV.
- Improved image resolution does not inherently reduce the surface-area effect.
Conclusions:
- The surface-area effect significantly impacts low-energy electron dosimetry in 3D image-based models.
- A tenfold increase in image resolution could mitigate dosimetry errors for low-energy electrons.
- Alternative methods for defining the bone-marrow interface, like polygonal isosurfaces, offer dosimetry improvements without requiring higher resolution.