Task Group 123
Classification of Harmful Radiation-induced Effects on Human Health for Radiological Protection Purposes

A Task Group under Committee 1 and Committee 4

Background

Publication 103 indicates that health objectives of the Commission’s system of radiological protection are to manage and control exposures to ionising radiation so that:

  • Harmful tissue reactions are prevented, and
  • The risks of stochastic effects are reduced to the extent reasonably achievable.

With regards to these objectives, the classification of health effects into two distinct categories, tissue reactions and stochastic effects, directly underpins the implementation of the system of radiological protection.

Currently, tissue reactions are defined as ‘injury in populations of normal cells characterised by a threshold dose and an increase in the severity of the reaction as the dose is increased further’. Stochastic effects are defined as ‘effect resulting from damage in a single cell, such as cancer and heritable effects. The frequency of the event, but not its severity, increases with an increase in the dose. For protection purposes, it is assumed that there is no threshold dose’. (Both definitions are taken from ICRPædia).

There has been debate with regards to the adequacy of the current scheme for classification of health effects with current scientific evidence (for example, see ICRP 2021 virtual workshop). For protection purposes, it may be useful to distinguish between severe and other tissue reactions or between short-term and long-term health effects, or to add a third category of effect as some health effects may not fit well into either category such as cataract or diseases of the circulatory system.

While introducing the process of revision of the Commission general recommendations, Clement et al. indicated ‘the classification of harmful radiation-induced health effects into ‘stochastic effects’ (cancer and heritable diseases) and ‘harmful tissue reactions’ for protection purposes should be revisited to ensure that it remains fit for purpose’. This and the above questions highlight the need for a review of the ICRP scheme for health effects classification.

Mandate

The Task Group will:

  1. Clarify the rationale behind the current classification (based on a review of relevant ICRP Publications) and the primary protection objectives of the ICRP System;
  2. Assess the reasons calling for an evolution based both on a review of scientific literature and relevance for the radiological protection objectives; and,
  3. If any evolution is deemed desirable from a scientific point of view, assess the impact on practical management of radiological risk with regards to the radiological protection system objective, for both the prevention of harmful tissue reactions and the limitation of stochastic effects.

Over the 3 stages described above, attention will be paid to the management of various source of uncertainties: underlying mechanisms, threshold dose, individual sensitivity, etc, as well as to other potential developments to the system being considered by other Task Groups. Protection objectives will be discussed on the basis of specific exposure situations (e.g. when considering exposure of a patient, tissue reaction may not be prevented while exposure is justified as doing more good than harm).

Process

The kick-off meeting of the Task Group (T0) will aim at developing a common understanding of the Task Group objectives between members and to identify key publications, report, articles, etc. to be reviewed in order to achieve steps 1 and 2. A work plan, assignments and timeline will be developed and agreed on. An online topical workshop is planned shortly after the meeting to gather ideas and information from interested parties.

A 2nd Task Group meeting (T0+1 year) will aim at presenting outcomes from steps 1 and 2. Results will be discussed with regards to the current classification. These elements will be used to feed step 3 work. A Table of content for a draft report will be developed. Writing assignments will be agreed on.

A draft report will be prepared and submitted to critical reviewers from C1 and C4 (T0+2 years). Results of the reviews will be taken into account to prepare a new draft report for MC reviewers. Comments will be used to prepare a report for public consultation. A 3rd Task Group meeting (T0+3 years) is planned to consolidate this document. An online topical workshop is planned before the public consultation process starts.

Results of the public consultation will be used to prepare a final draft report for C1 and C4 reviewers and MC reviewers. The process will result in a final report for MC approval for publication (anticipated to be at T0+4 years). An online topical workshop is planned to detail how comments received during public consultation were implemented and the Publication.

The Task Group will interact as required with other relevant Task Groups, such as TG111 (factors governing the individual response of humans to ionizing radiation), TG119 (circulatory diseases) or TG121 (heritable effects). The Task Group will also interact with organisations in formal relations with ICRP, including among others IAEA, IRPA, MELODI, NEA and UNSCEAR.

Deliverables

The Task Group will develop a report for publication in the Annals of the ICRP addressing the rationale behind the current classification of health effects and providing a review of scientific evidence which questions this classification. Discussion on the need for an evolution of the classification with regards to the objectives of protection of the system will be provided (pros and cons) and, if required, an updated classification scheme will be proposed. In addition, the Task Group will develop materials suitable for ICRPædia in collaboration with the Scientific Secretariat.

Ludovic Vaillant (Chair), CEPN, France
Elizabeth Ainsbury (Vice-Chair), UK Health Security Agency, United Kingdom
Friedo Zlzer (Vice-Chair), University of South Bohemia, Czech Republic