Meeting of the NEA/CRPPH
Expert Group on International Recommendations
To Assess the ICRP Draft Recommendation on
Radiation Detriment Calculation Methodology
6 May 2020
The Nuclear Energy Agency (NEA) Committee on Radiological Protection and Public Health (CRPPH) has for some time been working with the ICRP to provide constructive user comments on draft recommendations. The CRPPH Expert Group on International Recommendations (EGIR) met electronically on the 6th of May, 2020, to provide comments on the ICRP draft recommendation, “Radiation Detriment Calculation Methodology”. Participation is listed in Annex to this summary.
Given that the EGIR was not able to meet in person, due to the corona virus pandemic, discussions and exchanges were somewhat physically limited. Having only 2 hours there was insufficient time to hold discussions of a general nature, and of text changes to suggest. The EGIR thus focused on general comments, but encouraging participants to develop their own suggested textual changes. The following is a summary of the general comments that the EGIR offers to the ICRP for consideration.
Overall View
• The EGIR participants agreed that objective of this draft recommendation is to provide an explanation of what radiological detriment is currently intended to be, including detailed calculations and traceability of the data used. Although annexes A, B, and C of ICRP 103 cover much of this information, the draft recommendation is an all-in-one-place summary of how detriment is calculated in ICRP Publication 103. This is, in particular for new and midcareer radiological protection experts, a useful summary of the concept and quantity of radiological detriment.
• An added-value of this document could be, with some modification, the summary of relevant experience gained and research undertaken since the publication of ICRP 103, and the specification of the “application” of the concept of detriment.
• The EGIR recognised that UNSCEAR 2012 made a distinction between lowdose exposures, whose possible effects are conjectural, and higher-dose effects, whose effects are statistically attributable. In order to have a sciencebased understanding of detriment, detriment from higher doses could be expressed separately from detriment from lower doses. This distinction is particularly important in terms of the hereditary component of detriment. Hereditary aspects of detriment are assumed rather than seen in exposed humans, thus meriting their separate expression from cancer detriment. This distinction is also important in terms of detriment from collective dose, which, if summed over very small doses is conjecture rather than statistics.• It should be noted in the report that the concept of attributability is linked to doses that have already occurred, rather than to prospective doses
• The use of only 2 generations to express hereditary risk was seen as an area that should be more clearly explained.
• ICRP 99, on which the description of detriment in ICRP 103 is based, should be included in the list of references of this document.
Individual versus Population Focus
• This draft report is helpful to understand how the radiation detriment has been calculated in the ICRP system of radiological protection. However, the ICRP view on the issues of "population approach” vs "individual approach” in radiological protection is not still clearly written in this draft report. For example, in para. (6), it states that methods of controlling sources of exposure are usually applied without reference to individual profiles of those exposed, and it states that it is desirable to set standards and to optimise protection in ways that are independent of age, sex and region of the world. This might be true for the planned exposure situations, but we should recognize the fact that it is not the case with some circumstances in emergency and existing exposure situations including the post-accident circumstance where the protection of children, pregnant women and elderly people should be prioritized. Also, in para (7), it states that it should be noticed that there are significant differences in risk between sexes and in respect of age at exposure, and for the estimation of the likely consequences of an exposure of a given individual or population, it is preferable to use specific data relating to the exposed individuals when they are available, but this sentence is not well organized in explaining the protection approach mentioned in para (6). The statement in para (7) regarding retrospective use of detriment: radiation detriment can be used to assess risks in retrospective situations for exposures of identified individuals; should be modified to acknowledge the last sentence in the paragraph: it is preferable to use specific data relating to the exposed individuals when they are available.
• The EGIR noted that ICRP 101b, describing optimisation, recommends that protection should be optimised to protect the group most at risk. In an emergency exposure situation the group most at risk will often be children, but there is no calculation of detriment for the 0 – 18 year-old group. It is also stated that detriment to the embryo is equivalent to detriment to a new-born. The EGIR suggested that this should be revisited.
Evolution of the System
• Chapter 5, on possible evolution, would have been a good opportunity to discuss in detail science- and judgement-based updates to the concept of detriment. For example, detriment calculation and use for children, revisiting of detriment to the lens of the eye, use of age- and gender-specific criteria rather than age and gender averaged, etc. These could be presented as changes that could be made based on experience since the publication of 103, and changes that might be studied based on what seems to make sense at the moment.
• Given the recent focus of ICRP on ethical aspects of radiological protection, the EGIR felt that the ethical aspects of detriment, particularly in terms of using weighted averages, could have been discussed to express the views of the ICRP.
• The stochastic and/or deterministic nature of lens opacity from exposure of the eye should be more explicitly discussed. The ease of treatment using modern medical techniques should be considered in terms of weighting factors.
Numeric Updates
• Increasingly, epidemiology studies are showing statistically significant, casespecific excess risks at decreasing exposures, on the order of a few tens of mSv. This could affect the current distinction between “low dose” and “high dose”, between where risk is conjectural, and where risk is attributable. This should be discussed in the document.
• The EGIR is pleased to note that the ICRP is working towards issuing updated weighting factors, which would have an influence on the calculation of detriment.
Concept Relationships
• This report should further discuss how to consider sex- and age-related variation in determining the values of tissue weighting factors (e.g., Executive Summary (g)).
• The relationships between detriment and risk, and between detriment and effective dose, are important, particularly in terms of stakeholder dialogue. This document would have been a good area for ICRP to provide clear descriptions of these relationships.• The EGIR felt that this document would have been a good opportunity to describe how radiological detriment is intended to be used, what it represents, and over what range of exposures the mathematics used for its calculation are valid. A discussion of how radiological detriment is related to risk and to equivalent dose would also have been useful.
• Radiation detriment is significantly dominated by cancer, so detriment could be viewed as a good comparator for other causes of cancer, given all the other wider uncertainties. However, comparing a complex multi-faceted parameter for radiation exposure with data for death rates from other hazards is equivalent to comparing ‘apples with pears’. The ICRP should therefore consider addressing the relationship between radiation detriment and the risk of cancer death from radiation. This would then allow the possibility of a more valid basis for the comparison of risks from various hazards.
Annex
EGIR Meeting Participants
14:30 – 16:30, 6 May 2020
Participants
Dr Haru Ogino, NRA, Japan
Dr Abel Gonzelez, Argentina
Mr Yann Billarand, IRSN, France
Dr Marie-Claire Cantone, Milan Uiversity, Italy
Dr Debor Quayle, Health Canada, Canada
Contributing CRPPH Members and Nominees
Dr Malgorzata Sneve, DAS, Norway
Dr Graham Smith, GMS Abingdon Ltd, UK