By
. ICRP
Description
The ICRP Publication 66 Human Respiratory Tract Model for Radiological Protection (HRTM) has been applied to calculate dose coefficients
(doses per unit intake) and bioassay functions in ICRP Publications 68, 71, 72 and 78. For these purposes, ICRP assigned numerical values
to a range of model parameters, such as the size of the inhaled particles and the breathing rate of the subjects. These are known as
`default' or `reference' values, and were chosen to be typical, representative values. In any particular situation the actual values
of many parameters can be considerably different from the reference values. Usually, doses from intakes of radionuclides are low compared
with the relevant limit or constraint, and the resulting difference is unimportant.
There are, however, circumstances where more
reliable assessments of intake and dose are desirable. This Guidance Document therefore gives advice on applying specific information
within the framework of the HRTM for assessing occupational and environmental exposures and for interpreting bioassay data. Chapters
on each aspect of the model (morphometry, physiology, deposition, clearance, gases and vapours, dosimetry) provide: A summary of how
the HRTM treats that topic; Information on the reference values of relevant parameters; Guidance on choosing between default values;
Information on how doses and bioassay quantities (lung retention, urine, and faecal excretion) vary with the values of selected parameters,
giving guidance on the importance of obtaining specific information; Simple examples of the use of specific information relating to the
topic.
Annexes give additional information for those directly involved in applying the HRTM to specific situations, including
guidance on obtaining parameter values. A brief overview is given of the deposition, characterisation, and sampling of aerosols, with
references to further information, as there are relevant text books already available. Issues specific to radioactive aerosols, such
as low particle number concentrations for high specific activity materials are, however, addressed. Guidance on obtaining information
about absorption of inhaled radionuclides into blood is given in greater detail, because this is a topic on which ICRP has traditionally
given guidance, and because a compilation of such information is not readily available elsewhere. Several detailed examples are also
provided. One involves assessment of an individual's intake and committed dose from comprehensive bioassay monitoring data. The others
deal with the derivation of HRTM absorption parameter values from experimental data, and their application, with additional information
on e.g. size distribution, to calculate dose coefficients and interpret bioassay data.
Included in series
International Commission on Radiological Protection
