Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
mineral bone surfaces (trabecular and cortical), and mineral bone volumes (trabecular
and cortical). Target tissues considered were: active marrow (surrogate tissue for the
hematopoietic stem and progenitor cells), and a revised 50-µm model of the skeletal
endosteum (surrogate tissue for the osteoprogenitor cells) (see ‘Endosteum’ in the
Glossary). Absorbed fractions for internalised alpha particles and neutron-generated
recoil protons were established based on path length-based transport algorithms given
in Jokisch et al (2011a, 2011b). Values of absorbed fractions to active marrow and
endosteum for internally-emitted photons and neutrons were obtained by first tallying
energy-dependent particle fluences within the spongiosa and medullary cavity regions
of the Publication 110 reference adult male and female voxel phantoms (ICRP, 2009)
and then applying fluence-to-absorbed dose response functions (DRFs). Further
details on the derivations of these photon and neutron skeletal dose-response
functions are given in Johnson et al (2011) and Bahadori et al (2011), respectively, as
well as in Annexes D and E of Publication 116 (ICRP, 2010).
1.7 Interpretation of bioassay data
(42) The system of dose assessment from bioassay data that is generally applied
relies first on the evaluation of the intake of a radionuclide either from direct
measurements (e.g. external monitoring of the whole body or of specific organs and
tissues) or indirect measurements (e.g. of urine, faeces or environmental samples).
Predicted values of these measured quantities for unit intake of a radionuclide are
recommended by ICRP and these values can be used to estimate the intake (ICRP,
1997b). The committed effective dose resulting from any intake is then calculated
using the appropriate dose coefficient recommended by ICRP or determined using
ICRP’s recommended methodology. In some cases national authorities require the
assessment of the intake of a radionuclide as well as formal assessment of dose. The
data provided also serve this purpose.
(43) It is possible, as discussed by Berkovski et al (2003a), to calculate committed
effective dose directly from bioassay measurements using functions that relate them
to the time of the intake. The main advantage of this approach is that the user does not
perform the intermediate step of calculating the intake in order to evaluate the dose.
This eliminates the risk of using bioassay functions calculated with a particular
biokinetic model and dose coefficients derived from a different (earlier or more
recent) version of that model. This has been shown to be a rather frequent cause of
miscalculations in intercomparison exercises (IAEA, 2007).
(44) Whichever approach is adopted, the assessed dose is in many cases less
sensitive to the choice of parameter values than is the assessed intake. Berkovski et al
(2003a) showed that for a number of chemical forms of radionuclides the ‘dose per
unit content’ is largely insensitive to the choice of inhaled particle size for a wide
range of measurement times following an intake. In such circumstances the need for
specific information on the appropriate activity median aerodynamic diameter
(AMAD) of an aerosol may not therefore arise. Similarly, dose per unit content may
be insensitive to the choice of absorption Type for the specific chemical form
involved, for specific ranges of measurement times after the intake.) Care is still
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