Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
1.6.2 Adult Reference Computational Phantoms, Publication 110 (ICRP,
2009)
(39) Traditionally, stylised computational phantoms of human anatomy have been
utilised for assembling dose coefficients for both external and internal radiation
protection. These phantoms are constructed using mathematical surface equations to
describe internal organ anatomy and exterior body surfaces of reference individuals
(Cristy, 1980; Cristy and Eckerman, 1987), and as such, are limited in their ability to
capture true anatomic realism completely. As an alternative format for radiation
transport simulation, voxel phantoms are based on segmented tomographic data of
real individuals obtained from computed tomography or magnetic resonance imaging
(Zankl et al, 2002, 2003, 2007). As outlined above, the 2007 Recommendations
adopted the use of realistic anatomical models for the revision of dose coefficients for
both internal and external radiation sources. Publication 110 (ICRP, 2009) describes
the development and intended use of the computational phantoms of the ICRP adult
Reference Male and Reference Female. The reference phantoms were constructed
after modifying the voxel models of two individuals whose body height and mass
closely matched reference values. Organ volumes of both models were adjusted to
yield organ masses consistent with ICRP reference data given in Publication 89
(ICRP, 2002a) without compromising their anatomic realism regarding organ shape,
depth, and position in the body. The report describes the methods used for this
process and the anatomical and computational characteristics of the resulting
phantoms.
(40) The computational phantoms of adult Reference Male and Female may be
used, together with codes that simulate radiation transport and energy deposition, for
the assessment of the mean absorbed dose, DT, in an organ or tissue T, from which
equivalent doses and the effective dose may be successively calculated.
1.6.3 Advances in skeletal dosimetry
(41) In this report, the skeletal dosimetry models of Publication 30 (ICRP, 1979)
have been substantially updated for all radiations emitted from internalised
radionuclides – alpha particles, electrons, beta particles, photons, and neutrons (e.g.
from spontaneous fission). Improvements over the Publication 30 model include a
more refined treatment of the dependence of the absorbed fraction on particle energy,
marrow cellularity, and bone-specific spongiosa micro-architecture. Two reference
sets of skeletal images were established for radiation transport simulation. The first
included 1-mm ex vivo CT images of some 38 skeletal sites harvested from a 40-year
male cadaver (Hough et al, 2011). These images were used to establish fractional
volumes of cortical bone, trabecular spongiosa, and medullary cavities by skeletal
site, and to serve as the macroscopic geometric model for particle transport. The
second included 30-µm microCT images of cored samples of trabecular spongiosa to
establish fractional volumes of trabecular bone and marrow tissues, and to serve as
the microscopic geometric model for particle transport. Both image sets were then
combined during paired-image radiation transport (PIRT) of internally emitted
electrons (Shah et al, 2005). Source tissues were: bone marrow (active and inactive),
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