Image-based pediatric skeletal dosimetry for the UF hybrid computational phantom series

Abstract

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Objectives: The purpose of this study was to perform internal electron skeletal dosimetry computations for the UF hybrid computational phantom series utilizing 30-micron resolution microCT images of skeletal specimens via autopsy.

Methods: Internal electron absorbed fraction calculations from active marrow (TAM), trabecular bone volume (TBV), and cortical bone volume sources to TAM targets were then computed utilizing Paired-Image Radiation Transport (PIRT) EGSnrc simulations, which simultaneously accounts for both cortical bone cross-fire into the active marrow and electron energy escape from the physical bone structure.

Results: In the newborn lumbar spine, PIRT electron absorbed fraction TAM target results showed differences up to 64% less for a TBV source and up to 2 times less for a TAM source for intermediate electron energies compared to current infinite transport calculations due to electron escape. For high electron energies, up to 10 times less for a TBV source and up to 18 times less for a TAM source. PIRT results have shown up to 11% energy deposition into active marrow from a cortical bone source in the newborn lumbar spine, while current models assume zero deposition.

Conclusions: Realistic dose estimates in the relevant skeletal target tissues become increasingly important in pediatric patients. Current pediatric models do not account for energy escape, cortical bone cross fire, or cellularity changes during transport. PIRT was utilized to revise the current pediatric skeletal dosimetric computations by addressing these limitations. These revised absorbed fractions will be utilized to improve of photon fluence-to-dose response functions and specific absorbed fractions.

Research Support: Supported by the DOE NE/HP Fellowship.