Occupational Intakes of Radionuclides Part 1 - ICRP

4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
DRAFT REPORT FOR CONSULTATION
6 GENERAL ASPECTS OF RETROSPECTIVE DOSE ASSESSMENT
6.1 Introduction
(300) The effective dose calculated for protection purposes is determined from the
equivalent doses to organs and tissues of the human body, which are in turn calculated
from the mean absorbed doses to those organs and tissues (Section 1.2). Effective
dose provides a value which takes account of the given exposure conditions but not of
the characteristics of a specific individual. In particular, the tissue weighting factors
that are used to determine effective dose are selected, rounded values representing
averages over many individuals of different ages and both sexes. The equivalent doses
to each organ or tissue of the Reference Male and the Reference Female are averaged,
and these averaged doses are each multiplied with the corresponding tissue weighting
factor to determine the sex-averaged effective dose for the Reference Person (ICRP,
2007). It follows that effective dose does not provide an individual-specific dose but
rather that for a Reference Person under given exposure conditions (ICRP, 2007).
(301) There are two alternative approaches that may be applied for retrospective
dose assessment:
a) The calculation of the intake of a radionuclide either from direct
measurements (e.g., measuring the activity of radionuclides in the whole body
or in specific organs and tissues by external counting) and/or from indirect
measurements (e.g., measuring the activity of radionuclides in urine or faeces,
or exposure monitoring in the workplace). Biokinetic models are used to
interpret the measurements and the effective dose is calculated from the intake
using reference dose coefficients (doses per unit intake, Sv Bq -1 )
recommended by ICRP or determined using ICRP’s recommended
methodology (ICRP, 2007).
b) Calculation of the committed effective dose directly from the measurements
using functions that relate them to the time of the intake. The measurements
could be of whole body or organ content, activity in 24 hour urine or faecal
samples, or concentration of radionuclides in air in the workplace. For the
interpretation of bioassay data, this approach requires the use of tables of
‘dose per unit content’ as a function of time after the intake (ICRP, 2007).
The two approaches are equivalent and should produce identical results provided the
same biokinetic models, parameter values and assumptions are used.
(302) ‘Dose per unit content’ tables for selected radionuclides are given in this
report series and on the accompanying CD-ROMs. They provide data on the
committed effective dose corresponding to values of bioassay quantities measured at
specified times after an acute intake of the radionuclide. A more detailed description
of the data provided is given in Section 7.3. The tables provide a simple and easy-touse
tool, which should promote harmonisation in the interpretation of bioassay data.
(303) There may be some circumstances in which parameter values may be changed
from the reference values in the calculation of effective dose. It is, therefore,
114