Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
present in the kinetics of a chain member, but not in the kinetics of the chain parent,
also receive a transfer of transformations from the chain member’s ‘Other tissues’
based on a mass fraction computed using the parents m (OT)
.
(244) The first approach of Annexe C.3 (ICRP, 1995) redistributes transformations
after the given biokinetic models are solved, whilst the second effectively ‘automates’
the process by amending the biokinetic models before solving them. In the latter
approach any global sources not included in a chain member’s local sources are added
to the chain member’s model and represented by the same number of compartments
specified for their ‘Other tissues’, each with the same kinetic transfer pathways. The
rates of loss from these compartments are the same as the corresponding ‘Other
tissues’ compartments but the transfer rates to them are mass fractions of those of the
corresponding ‘Other tissues’ compartments. The transfer rates to the ‘Other tissues’
compartments are decremented accordingly. Although both approaches give similar
results, the latter is considered to be more rigorous and is used here.
3.7.3 Bioassay data
(245) A number of issues should be noted regarding the use of biokinetic models for
the retrospective assessment of doses from bioassay data:
(a) As explained in Section 1.4, equivalent dose coefficients for organs and
tissues are calculated separately for the Reference Male and Reference Female and
then averaged in the calculation of effective dose. Some biokinetic models have sexspecific
parameter values, and so a number of possible methods could be
implemented to determine effective dose from bioassay measurements:
i. Equivalent doses to organs per unit content of a bioassay quantity could be
calculated separately for males and females. Equation 1 (Section 3.7) would
then be applied to determine effective dose per unit content.
ii. Intakes could be calculated separately for males and females. The dose
coefficient would then be applied to the average intake.
iii. The intake could be calculated with sex-averaged biokinetic data, and the dose
coefficient would then be applied to this intake. Biokinetic model parameters
could be averaged, or predicted retention/excretion functions could be
averaged.
iv. The intake could be determined only with the male (or female) biokinetic
model. The dose coefficient would then be applied to this intake.
Since effective dose is a protection quantity that provides a dose for a Reference
Person rather than an individual-specific dose, significant advantages arise from
adopting a simple approach to retrospective dose assessment. For this reason,
method (iv) has been adopted in this series of reports, with the intake determined
using the male biokinetic model where sex-specific models are provided. It is
recommended that this method should be adopted for the interpretation of bioassay
data.
(b) In the dose per unit content functions for retained activity presented in
subsequent reports of this series, all activity within the body (including contents of the
urinary bladder and the alimentary tract) is included. For the lungs, all activity in the
thoracic region of the respiratory tract, including the thoracic lymph nodes, is
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