Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
chronic intakes are not given in this publication, but equilibrium values of bioassay
quantities for continuous chronic exposure are provided for some radionuclides.
6.4.5 Influence of decorporation therapy
(349) In cases involving internal contamination, blocking, dilution, or chelating
agents may be used to enhance the clearance of the activity from the body and reduce
committed doses. The use of interventional techniques to enhance the body’s natural
elimination rate of the compound, or possibly to block the uptake of the radionuclide
in sites where high uptake may occur (e.g., radioiodine in the thyroid), may partially
or completely invalidate the use of standardized model approaches described above to
estimate the intake and dose (NCRP, 2009).
(350) The use of chelating agents such as DTPA, for example, may influence
excretion rates for weeks or months after cessation of treatment.
(351) It is not feasible to give specific advice as the treatment of any bioassay data
depends upon the circumstances of the exposure and the need and timescale required
for the dose assessment.
6.4.6 Wounds
(352) Because of their nature, intakes of radionuclides resulting from contaminated
cuts or wounds typically account for an appreciable proportion of high dose
exposures. Radionuclides may be transferred from the wound site to blood and to
other organs and tissues, and the NCRP has developed a model to describe this
transfer for various chemical forms of selected radionuclides (NCRP, 2007). Coupled
with an element-specific systemic biokinetic model, the NCRP model can be used to
calculate committed doses to organs and tissues and committed effective doses
following transfer of the radionuclide to the blood and systemic circulation, as well as
to predict urinary and faecal excretion.
(353) As noted in Section 3.1, the assessment of internal contamination resulting
from wounds is in practice treated on a case-by-case basis using expert judgement. In
many cases, the amount of a radionuclide transferred from a wound site to blood may
be assessed directly from urine bioassay data. Section 3.4 summarises the main
features of the NCRP model, since this information may be of use in the interpretation
of bioassay data for individual cases of wound contamination.
6.5 Uncertainties in Internal Dose Assessment Based on Bioassay
(354) Publication 103 (ICRP, 2007) makes the following statement with respect to
the assessment of uncertainties:
In order to assess radiation doses, models are necessary to simulate the
geometry of the external exposure, the biokinetics of incorporated
radionuclides, and the human body. The reference models and necessary
reference parameter values are established and selected from a range of
experimental investigations and human studies through judgements. For
regulatory purposes, these models and parameter values are fixed by
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