Dose Coefficients for Intakes of Radionuclides by Members of the Public: Part 1

ICRP CONSULATION ON:

DOSE COEFFICIENTS FOR INTAKES OF RADIONUCLIDES BY MEMBERS OF THE PUBLIC: PART 1

 This publication is the first in a series of three reports providing dose coefficients for radionuclides inhaled or ingested by members of the public. This series will replace the Publication 56 series and the compilation provided in Publication 119.

The report is an important part of the overall colossal task of revising all dose coefficients following from the 2007 Recommendations (Publication 103) and changes made to radiation and tissue weighting factors as well as the introduction of anthropomorphic phantoms for dosimetry.

The series of reports on public dose coefficients follows publication of dose coefficients for workers for external sources (Publication 116) and ingested and inhaled radionuclides (Publications 130, 134, 137, 141, 151) and external exposure of members of the public (Publication 144). Much work remains to be done to complete the task of revision of dose coefficients for compliance with the 2007 Recommendations. As well as the other two parts of the series on public dose coefficients for intakes of radionuclides, work is in progress to revise all dose coefficients for radiopharmaceuticals to replace the values in the compendium available as Publication 128 and add values for radiopharmaceutical that have more recently come into use. In addition, ICRP has embarked on the provision of dose coefficients for medical diagnostic x-ray procedures.

The report under review is testament to the quality of the work undertaken on behalf of ICRP by expert groups collaborating in the review of biokinetic data, development of biokinetic models, and calculation and assembly of dose coefficients with rigorous quality control. The printed report provides committed effective dose coefficients; more extensive data to include equivalent dose coefficients to tissue/organs for males and females of the age groups considered will be available electronically. It is very helpful to have detailed explanation of the science and models developed from it and notable that considerable efforts have been made to ensure that the most recent science has been applied. Users of dose coefficients will be able to apply the most appropriate values, taking account of chemical form and other characteristics of the ingested or inhaled radionuclides under consideration. Furthermore, the model descriptions will allow calculations to be done for radionuclide exposures in situations where the dose coefficients provided are not considered adequately representative.

The ICRP, and specifically Committee 2 and its task groups, are to be congratulated on the extensive programme of work to provide dose coefficients. A number of questions arise:

• An omission from this report (and others) is compilations of dose coefficients (as in Publication 119) and comparison of new dose coefficients with previously provided values. Comparisons would be very helpful, particularly to highlight cases where there have been substantial changes. In such cases, it would further be very helpful to have an explanation of the reasons for changes. As it is, the user is required to identify changes and identify possible causes.
• It would be helpful if ICRP could emphasise that users should make efforts to apply dose coefficients that are best estimates for the specific situations of exposure under consideration. Conservatism should not be introduced at the stage of the calculation of doses. ICRP has stated previously, and could helpfully reiterate, that users should change model parameter values related to chemical form if the forms considered in the report are not sufficiently representative of the form under consideration.
• It would be helpful if ICRP could provide a timescale for completion of the work on public dose coefficients, and separately for dose coefficients for patients for radiopharmaceuticals and diagnostic x-ray procedures. As it has taken 16 years to get this far, it seems possible that completion of this task could be a limiting factor on the publication of the next set of general recommendations?
• Has ICRP given thought to whether another round of revision of dose coefficients would be necessitated by revisions to general recommendations? Revision of all low-dose risk estimates and hence changes to detriment and relative detriment values, and consequent changes to tissue weighting factors, should perhaps be avoided if they are too small to materially affect radiation protection practice, given that they would result in the requirement for so much work by ICRP and the users of dose coefficients with little if any benefit. The same applies to any changes to radiation weighting factors. It is noteworthy that the report under review has a very well-written section on sources of uncertainties in models and their underlying data, although wisely no attempt is made to assign overall uncertainties – dose coefficients are calculated as reference values. However, it must be the case that small differences will be well within uncertainty ranges.

UK Society for Radiological Protection (SRP)

UK Committee on Medical Aspects of Radiation in the Environment (COMARE)