Revised estimates of electron absorbed fractions and radionuclide S values in trabecular bone
- Texas A&M Univ., College Station, TX (United States)
One of the more difficult areas of nuclear medicine dosimetry is estimating radiation energy deposition in bone. In many dose calculations involving charged particles, boundary effects are ignored and absorbed fractions of energy (AF) are assumed to be equal to unity when the target region corresponds to the source region and zero otherwise. For more complex structures, such as trabecular bone, these simplifying assumptions are not appropriate and more sophisticated approaches are necessary. In this work, we report estimates of AFs for monoenergetic electrons based upon EGS4-PRESTA transport calculations and a spherical shell model of trabecular bone. In this model, an spherical bone marrow cavity is initially created whose mean chord length (2/3 the diameter) is selected from a chord length distribution based upon the measurements of F.W. Spiers. Two concentric spherical shells are next placed around the cavity: an endosteal layer 10 {mu}m in thickness, and a layer of trabecular bone whose thickness corresponds to measured trabeculae chord length distributions. Nine sites within the adult skeleton are considered for electron sources in the bone volume, on the bone surface, and in marrow cavities. Revised S values are also evaluated. For volume electron sources, our model indicates AFs to the marrow which fall below the energy-independent ICRP 30 value of 0.35 at electron energies below {approximately}500-keV. At higher energies, AFs increase to as much as 0.68 in the parietal bone at 4 MeV. When the target is the endosteum, AFs generally exceed the ICRP 30 energy-independent value of 0025 for all electron energies and all bone locations.
- DOE Contract Number:
- FG05-88ER60707; FG03-94ER61846
- OSTI ID:
- 441631
- Report Number(s):
- CONF-950603-; ISSN 0161-5505; TRN: 96:002093-0056
- Journal Information:
- Journal of Nuclear Medicine, Vol. 36, Issue Suppl.5; Conference: 42. annual meeting of the Society of Nuclear Medicine, Minneapolis, MN (United States), 12-15 Jun 1995; Other Information: PBD: May 1995
- Country of Publication:
- United States
- Language:
- English
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