Task Group 122
Update of Detriment Calculation for Cancer

A Task Group under Committee 1

Background

Calculation methodology and perspectives on the evolution of radiation detriment have been reviewed recently by ICRP Task Group 102 on Detriment Calculation Methodology in ICRP Publication 152 (2022, in press). The Task Group performed an in-depth review of detriment calculation as presented in ICRP Publication 103, detailing each step of detriment calculation, associated parameters, models, and hypothesis.

Detriment calculation methodology is a two steps process as detailed in (Clero et al., J Radiol Prot 2019, 2022). The first step to calculate nominal cancer risk coefficients for a set of organs and tissues, plus heritable effects. The second step is a weighting for cancer severity, based on judgements concerning lethality, quality of life, and years of life lost, to estimate detriment values for each organ or tissue. After standardisation of organ-specific detriments to obtain relative detriments, the overall radiation detriment is calculated as the sum of relative detriments, i.e., the relative contribution of each organ or tissue to the total radiation detriment is used to derive tissue weighting factors used for the calculation of effective dose.

Task Group 122 will also consider potential improvements to the calculation methodology with regard to the development of the future ICRP General Recommendations.
The current General Recommendations of ICRP were elaborated nearly 15 years ago. Detriment calculation methodology requires revision to reflect the evolution of scientific knowledge and guarantee adequate expert judgements in the ongoing process of revision of the system of Radiological Protection (Clement et al., J Radiol Prot 2021).

Mandate

The main objective of the Task Group is to evaluate the current knowledge on all aspects involved in the calculation of detriment for cancer, to assess the implications of updating components of detriment calculation where necessary and to consider potential modifications of detriment calculation. The objectives are specified below.

Several Task Groups have been or will be launched to consider specific and complementary aspects of the detriment. Specifically, Task Group 91 is dealing with the Dose and Dose Rate Effectiveness Factor (DDREF), Task Group 118 with relative biological effectiveness, Task Group 119 with diseases of the circulatory system, and Task Group 121 with the effects of ionising radiation exposure in offspring and next generations. These elements of the detriment will not be considered in the present Task Group.

1. Cancer risk models

Risk estimates in ICRP Publication 103 principally relied on Life Span Stucy (LSS) incidence data gathered up to the end of 1998 (Clero et al., J Radiol Prot 2019, 2022). The LSS as well as other cohorts have been updated since then, and new studies have been conducted. The objectives in this section are:

• To assess changes in knowledge about radiation-related risks of certain types of cancer and cancer overall since 2007.
• To investigate the transport of risks from the LSS (a Japanese population exposed in 1945) to other populations with different background risks of cancer (e.g., a 21st century Western workforce).
• To assess whether and how evidence of studies other than the LSS can be incorporated. Although the LSS data have a central role in radiation risk assessment, other sources of data are becoming more important, including studies of diagnostic and therapeutic medical exposures, pooled occupational studies, and studies of the consequences of the Chornobyl accident.

2. Calculation of nominal risks

The second step of the calculation of radiation detriment deals with the methodology and parameters used to calculate the nominal risk coefficients. The objectives in this section are:

• To consider how risks from a brief exposure (as experienced by the Japanese atomic-bomb survivors) can be translated to a chronic, protracted or fractionated exposure, i.e., the application of a Dose Rate Effectiveness Factor (DREF).
• To reconsider the exposure scenario in the calculation of the nominal risk coefficient including parameters and methodology as for example the dose, the attained age or the intervals for age at exposure.
• To investigate the optimal lifetime risk calculation method (risk of exposure induced cancer (REIC), lifetime attributable risk (LAR)) for the nominal risk coefficient calculation based on different parameters as, e.g., uncertainties, survival curve calculation, practical implementation or data availability.
• To reconsider the populations and age groups for which the nominal risk coefficients are calculated in order to allow and facilitate a more detailed practical application of the coefficients (e.g., for both sexes separately, for children below 18 years of age).

3. Weighting scheme for cancer severity

The objectives of the Task Group in this section are:

• To assess feasibility and relevance of an update of parameters used in Publication 103 to reflect changes in cancer diagnosis, treatment and survival over time.
• To investigate alternative methods for integration of nominal risk coefficients into a single quantity (detriment). This objective involves the quantification of the burden from cancer after diagnosis. The concept of Disability-Adjusted Life Years (DALY) will be evaluated for this purpose.

4. Reference population

The current detriment calculation process relies on risk models (mainly derived from a Japanese population), baseline rates (derived from 2 composite populations from Asia and Europe-North America), and lethality and severity parameters for cancer (derived from the USA). However, the interpretation of the current detriment is global. The objectives in this section are:

• To assess how heterogeneity in risk models by characteristics such as country, sex, age and background cancer risk factors leads to heterogeneity in detriment.
• To assess how heterogeneity in parameters of lethality and severity of cancers by characteristics such as country, sex, age and cancer risk factors contributes to heterogeneity in detriment.
• To evaluate the limitations of the current calculation method of the detriment, even with updated parameters and risk models, for generalization to all humans, and to suggest ways to overcome those limitations.

5. Suggestions for modifying the detriment calculation scheme for cancer

The results of the previous sections will be integrated into suggestions for a revised detriment calculation scheme for cancer. The objectives in this section are:

• To describe a scheme that integrates updates for cancer risk models, cancer severity weighting and reference population, ensuring a high level of quality assurance in the calculation procedures.
• To identify sources of uncertainty in updating the various parts of detriment calculation and estimate their impact.
• To investigate the feasibility and relevance of providing different values of detriment separately for males and females, and for specific age categories.
• To preliminarily assess the potential impact for the concept of effective dose and the tissue weighting factors used therein.
• To preliminarily assess the potential impact on radiological protection recommendations.

Process

In a first step, a kick-off in person Task Group meeting is planned to discuss ideas, identify important issues to be addressed, and finalize the programme of work of the Task Group.

In a second step, the Task Group will prepare a detailed report. The report will include a review of the current knowledge of risk models, methods to calculate nominal risks, weighting risks according to their health consequences, and stratification of both with regard to populations. Finally, the report will provide recommendations for further action, for all Committees and the Main Commission.

The Task Group will liaise with the UNSCEAR to exploit potential synergism with the CanEpi expert group on “Epidemiological studies on radiation and cancer”.

Deliverables

The Task Group will develop an ICRP publication that addresses the objectives described above. The major sections of the report will cover updates of cancer risk models, approaches to weight the severity of cancers and the application of risk and severity measures on a global population.

An open on-line Webinar will be organised by ICRP at the time of publication to summarize the main elements of the report.

In addition, the Task Group will develop materials suitable for ICRPædia in collaboration with the Scientific Secretariat.

Ludovic Vaillant (Co-Chair), CEPN, France

Richard Wakeford (Co-Chair), The University of Manchester, United Kingdom

Iulian Apostoaei (Member), USA

Nobuhiko Ban (Member), Nuclear Regulation Authority, Japan

Alina Brenner (Member), Japan

Enora Cléro (Member), French Institute for Radiological Protection and Nuclear Safety (IRSN), France

Markus Eidemüller (Member), Federal Office for Radiation Protection (BfS) , Germany

Samy El-Jaby (Member), Canadian Nuclear Safety Commission, Canada

Luana Hafner (Member), ENSI, Switzerland

Mark P. Little (Member), National Institutes of Health, USA

David Pawel (Member), USA

David Richardson (Member), University of California, Irvine, USA

Alexander Ulanowski (Member), International Atomic Energy Agency, Austria

Teun van Dillen (Member), National Institute for Public Health and the Environment (RIVM), Netherlands

Barrington Brevitt (Technical Secretary), Kingston Public Hospital South East Regional Health Authority , Jamaica