Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
Endosteum is not considered as all marrow (both active and inactive) within
50 µm of a bone surface, but is thought to be the surrogate tissue for the
osteoprogenitor cells, which are present along all bone surfaces regardless of
the marrow cellularity (mixture or percentages of active / inactive marrow).
The biokinetic models presented in this report may therefore have either a
“active marrow source” or a “trabecular marrow source” and specific
alpha/electron AFs will be produced for these two skeletal regions.
(239) Values of specific absorbed fractions at fixed energies are tabulated in
Publication 125 (ICRP, 2012). Specific absorbed fractions at the particular energies of
radionuclide emissions are found by interpolating the tabulated values using a
mathematical technique such as cubic splines.
3.7.2 Contribution of decay products to dose
(240) The dose coefficients given in this report series take into account the
contribution to dose from radionuclides produced in the body by ingrowth. However,
as in the past, it is assumed that no radioactive progeny are present in the initial intake
of the radionuclide for which the dose coefficient is determined, except for radon and
its progeny. Nuclear decay data are taken from Publication 107 (ICRP, 2008).
(241) The source region ‘Other tissues’ is commonly used in systemic models when
uptake is specified in particular organs and tissues and any remaining activity is taken
to be distributed in these other tissues. ‘Other tissues’ is the complement of the
explicitly designated tissues; that is, it is the set of all systemic tissues other than
those specified in the model. If independent kinetics are assumed for decay products,
each member of the decay chain may have different sets of specified source tissues,
and as a result the anatomic identity of ‘Other tissues’ varies among the chain
members. This can lead to anomalies when the biokinetic models are solved, such as
excess activity growing into one compartment at the expense of another. Annexe C.3
of Publication 71 (ICRP, 1995) outlines two alternative computational procedures that
seek to minimise these anomalies.
(242) To explain these approaches, it is useful to distinguish between local and
global sources. Local source tissues and local ‘Other tissues’ are both specific to each
chain member. Global sources incorporate all the chain’s local sources and global
‘Other tissues’ is the set of all systemic tissues other than the global sources. Thus for
the simple example of a two member chain where the parent’s local source is liver
and the decay product’s local source is kidneys, the corresponding global sources are
liver and kidneys and global ‘Other tissues’ includes all systemic tissues other than
liver and kidneys.
(243) The aim of the two approaches of Annexe C.3 (ICRP, 1995) is to redistribute
transformations from each chain member’s ‘Other tissues’ compartment to sources
r which are in the global set of source compartments but not the local set. For each
'
S
such source region,
'
r S , a mass fraction
( )
( )
'
m rS
of the chain member’s ‘Other tissues’
m OT
(OT) transformations is deducted from OT and transferred to this source '
r S . Sources
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