Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
mean absorbed dose for tissues that are members of ‘Other tissue’. Frequently ‘Other
tissue’ includes tissues assigned an explicit tissue weighting factor. For example,
breast tissue is rarely if ever explicitly noted in biokinetic models and thus its mean
absorbed dose is often based on its membership of ‘Other tissue’.
(399) Some uncertainties also arise in the manner in which the biokinetic models are
implemented in the dosimetric calculations. The biokinetic models are presented as
compartment models which in a dosimetric evaluation are further extended to include
the kinetics of radioactive decay and ingrowth of radioactive progeny. A number of
numerical methods are capable of solving the set of potentially large numbers (100s)
of coupled differential ‘stiff’ equations that describe the kinetics, although frequently
the demands of numerical accuracy have to be balanced with computational time.
Compartment-model issues contributing to uncertainties in the mean absorbed dose
include the assumed biokinetics of members of a decay chain (independent or shared
kinetics), and the representation of ‘Other’ tissues when their anatomical identity
varies among the decay chain members. (Section 3.7.2 and Annex C of Publication 71
(ICRP, 1995c)).
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