Accounting for beta-particle energy loss to cortical bone via paired-image radiation transport (PIRT)
- Department of Biomedical Engineering and Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, Florida 32611 (United States)
Current methods of skeletal dose assessment in both medical physics (radionuclide therapy) and health physics (dose reconstruction and risk assessment) rely heavily on a single set of bone and marrow cavity chord-length distributions in which particle energy deposition is tracked within an infinite extent of trabecular spongiosa, with no allowance for particle escape to cortical bone. In the present study, we introduce a paired-image radiation transport (PIRT) model which provides a more realistic three-dimensional (3D) geometry for particle transport in the skeletal site at both microscopic and macroscopic levels of its histology. Ex vivo CT scans were acquired of the pelvis, cranial cap, and individual ribs excised from a 66-year male cadaver (BMI of 22.7 kg m{sup -2}). For the three skeletal sites, regions of trabecular spongiosa and cortical bone were identified and segmented. Physical sections of interior spongiosa were taken and subjected to microCT imaging. Voxels within the resulting microCT images were then segmented and labeled as regions of bone trabeculae, endosteum, active marrow, and inactive marrow through application of image processing algorithms. The PIRT methodology was then implemented within the EGSNRC radiation transport code whereby electrons of various initial energies are simultaneously tracked within both the ex vivo CT macroimage and the CT microimage of the skeletal site. At initial electron energies greater than 50-200 keV, a divergence in absorbed fractions to active marrow are noted between PIRT model simulations and those estimated under existing techniques of infinite spongiosa transport. Calculations of radionuclide S values under both methodologies imply that current chord-based models may overestimate the absorbed dose to active bone marrow in these skeletal sites by 0% to 27% for low-energy beta emitters ({sup 33}P, {sup 169}Er, and {sup 177}Lu), by {approx}4% to 49% for intermediate-energy beta emitters ({sup 153}Sm, {sup 186}Re, and {sup 89}Sr), and by {approx}14% to 76% for high-energy beta emitters ({sup 32}P, {sup 188}Re, and {sup 90}Y). The PIRT methodology allows for detailed modeling of the 3D macrostructure of individual marrow-containing bones within the skeleton thus permitting improved estimates of absorbed fractions and radionuclide S values for intermediate-to-high energy beta emitters.
- OSTI ID:
- 20634686
- Journal Information:
- Medical Physics, Vol. 32, Issue 5; Other Information: DOI: 10.1118/1.1898463; (c) 2005 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BONE MARROW
BONE TISSUES
COMPUTERIZED TOMOGRAPHY
ENERGY LOSSES
ERBIUM 169
IMAGE PROCESSING
IMAGES
LUTETIUM 177
NMR IMAGING
PHOSPHORUS 32
PHOSPHORUS 33
RADIATION DOSES
RADIATION TRANSPORT
RADIOTHERAPY
RHENIUM 186
RHENIUM 188
SAMARIUM 153
SKELETON
STRONTIUM 89
YTTRIUM 90