WE‐E‐BRE‐01: An Image‐Based Skeletal Dosimetry Model for the ICRP Reference Adult Female – Internal Electron Sources

Abstract

Purpose:Limitations seen in previous skeletal dosimetry models, which are still employed in commonly used software today, include the lack of consideration of electron escape and cross‐fire from cortical bone, the modeling of infinite spongiosa, the disregard of the effect of varying cellularity on active marrow self‐irradiation, and the lack of use of the more recent ICRP definition of a 50 micron surrogate tissue region for the osteoprogenitor cells – shallow marrow. These limitations were addressed in the present dosimetry model.Methods:Electron transport was completed to determine specific absorbed fractions to active marrow and shallow marrow of the skeletal regions of the adult female. The bone macrostructure was obtained from the whole‐body hybrid computational phantom of the UF series of reference phantoms, while the bone microstructure was derived from microCT images of skeletal region samples taken from a 45 year‐old female cadaver. The target tissue regions were active marrow and shallow marrow. The source tissues were active marrow, inactive marrow, trabecular bone volume, trabecular bone surfaces, cortical bone volume and cortical bone surfaces. The marrow cellularity was varied from 10 to 100 percent for active marrow self‐irradiation. A total of 33 discrete electron energies, ranging from 1 keV to 10 MeV, were either simulated or modeled analytically.Results:The method of combining macro‐ and microstructure absorbed fractions calculated using MCNPX electron transport was found to yield results similar to those determined with the PIRT model for the UF adult male in the Hough et al. study.Conclusion:The calculated skeletal averaged absorbed fractions for each source‐target combination were found to follow similar trends of more recent dosimetry models (image‐based models) and did not follow current models used in nuclear medicine dosimetry at high energies (due to that models use of an infinite expanse of trabecular spongiosa).