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Specific absorbed fractions for a revised series of the UF/NCI pediatric reference phantoms: internal photon sources.

Abstract：

:Assessment of radiation absorbed dose to internal organs of the body from the intake of radionuclides or, in the medical setting through the injection of radiopharmaceuticals, is generally performed based upon reference biokinetic models or patient imaging data, respectively. Biokinetic models estimate the time course of activity localized to source organs. The time-integration of these organ activity profiles are then scaled by the radionuclide S value, which defines the absorbed dose to a target tissue per nuclear transformation in various source tissues. S values are computed using established nuclear decay information (particle energies and yields), and a parameter termed the specific absorbed fraction (SAF). The SAF is the ratio of the absorbed fraction (AF) - fraction of particle energy emitted in the source tissue that is deposited in the target tissue - and the target organ mass. While values of the SAF may be computed using patient-specific or individual-specific anatomic models, they have been more widely available through the use of computational reference phantoms. In this study, we report on an extensive series of photon SAFs computed in a revised series of the UF/NCI pediatric reference phantoms which have been modified to conform to the specifications embodied in the ICRP reference adult phantoms of Publication 110 (e.g., organs modeled, organ ID numbers, blood contribution to elemental compositions). Following phantom anatomical revisions, photon radiation transport simulations were performed using MCNPX v2.7 in each of the 10 phantoms of the series - male and female newborn, 1-year-old, 5-year-old, 10-year-old, and 15-year-old - for 44 different source and target tissues. A total of 25 photon energies were considered from 10 keV to 10 MeV along a logarithm energy grid. Detailed analyses were conducted of the relative statistical errors in the Monte Carlo target tissue energy deposition tallies at low photon energies and over all energies for source-target combinations at large intra-organ separation distances. Based on these analyses, various data smoothing algorithms were employed, including multi-point weighted data smoothing, and log-log interpolation at low energies (1 and 5 keV) using limiting SAF values based upon target organ mass to bound the interpolation interval. The final dataset is provided in a series of 10 electronic annexes in MS Excel format. The results of this study were further used as the basis for assessing the radiative component of internal electron source SAFs as described in our companion paper for this same pediatric phantom series.

journal_name

Phys Med Biol

journal_title

Physics in medicine and biology

authors

Schwarz BC,Godwin WJ,Wayson MB,Dewji SA,Jokisch DW,Lee C,Bolch WE

doi

10.1088/1361-6560/abc708

subject

Has Abstract

pub_date

2020-11-03 00:00:00

eissn

0031-9155

issn

1361-6560

pub_type

杂志文章

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Specific absorbed fractions for a revised series of the UF/NCI pediatric reference phantoms: internal photon sources.