Recommended citation
ICRP, 2022. Radiation detriment calculation methodology. ICRP Publication 152. Ann. ICRP 51(3).
Authors on behalf of ICRP
E. Cléro, L. Vaillant, W. Zhang, N. Hamada, D. Preston, D. Laurier, N. Ban
Abstract - Radiation detriment is a concept developed by the International Commission on Radiological Protection to quantify the burden of stochastic effects from low-dose and/or low-dose-rate exposures to the human population. It is determined from the lifetime risks of cancer for a set of organs and tissues and the risk of heritabl effects, taking into account the severity of the consequences. This publication provides a historical review of detriment calculation methodology since ICRP Publication 26, with details of the procedure developed in ICRP Publication 103, which clarifies data sources, risk models, computational methods, and rationale for the choice of parameter values. A selected sensitivity analysis was conducted to identify the parameters and calculation conditions that can be major sources of variation and uncertainty in the calculation of radiation detriment. It has demonstrated that sex, age at exposure, dose and dose-rate effectiveness factor, dose assumption in the calculation of lifetime risk, and lethality fraction have a substantial impact on radiation detriment values. Although the current scheme of radiation detriment calculation is well established, it needs to evolve to better reflect changes in population health statistics and progress in scientific understanding of radiation health effects. In this regard, some key parameters require updating, such as the reference population data and cancer severity. There is also room for improvement in cancer risk models based on the accumulation of recent epidemiological findings. Finally, the importance of improving the comprehensibility of the detriment concept and the transparency of its calculation process is emphasised.
© 2022 ICRP. Published by SAGE.
Keywords: Radiation detriment; Stochastic effects; Nominal risk; Sensitivity analysis.
Key Points
Radiation detriment is a concept developed by the International Commission on Radiological Protection to quantify the health impact of stochastic effects (cancer and heritable effects) from low-dose and/or low-dose-rate exposures for radiological protection purposes, considering both the probability of occurrence and the severity of these effects.
The procedure for calculating radiation detriment consists of two main parts: calculation of nominal risk (average estimate of lifetime cancer risk and risk of heritable effects associated with radiation exposure), and adjustment for severity in terms of quality of life in non-lethal conditions and length of life lost. Details of the procedure have been provided, which resolve ambiguity and correct misdescriptions, in Publication 103 (ICRP, 2007). Programming errors were found in the calculation of nominal risk for the working-age population in Publication 103. The Commission notes that these errors do not impact overall detriment and have no implications for the System of Radiological Protection.
Selected sensitivity analysis has demonstrated that sex, age at exposure, dose and dose-rate effectiveness factor, dose assumption in the calculation of lifetime risk, and lethality fraction have a substantial impact in the calculation of radiation detriment.
The calculation of radiation detriment needs to be updated to better reflect changes in reference population data and cancer severity parameters, variation of cancer risk with sex and age and between different populations, improvement in cancer risk models, and advances in risk estimation for heritable effects.
Executive Summary
(a) The concept of radiation detriment has been developed by the International Commission on Radiological Protection (hereafter, ‘the Commission’) for the purpose of radiological protection. It is defined as the excess of stochastic health effects in a group of individuals exposed to low-level radiation and their descendants compared with a non-exposed group. It is determined from sex-averaged and age-at-exposure-averaged lifetime risk estimates for a set of organs and tissues, taking into account the severity in terms of quality of life in non-lethal conditions and length of life lost.
(b) The Commission recently launched a thorough review of the System of Radiological Protection, taking into account the accumulation of practical experiences and advances in scientific understanding of radiation health effects since publication of the 2007 Recommendations (ICRP, 2007). The present publication constitutes part of this review.
(c) Radiation detriment is quantified assuming a linear-non-threshold (LNT) dose–response relationship for stochastic effects, and applying a dose and doserate effectiveness factor (DDREF) of 2 for solid cancers. This means that radiation detriment is applicable to a limited range of doses and dose rates.
(d) The values of radiation detriment should be considered not as projections of the absolute number of cases of cancer or heritable disease in a population, but as inferences based on reasonable assumptions for radiological protection.
(e) The methodology for calculating radiation detriment has developed over decades since the concept was first introduced in Publication 22 (ICRP, 1973). The most recent method in Publication 103 (ICRP, 2007) consists of two main parts. The first part is the calculation of nominal risk, which is the average estimate over age groups of the lifetime risk of cancer incidence and the risk of heritable effects associated with radiation exposure. The lifetime risk of cancer incidence is calculated for each of the reference populations (males and females of Euro-American and Asian populations), except for bone and skin cancers, and the results are averaged across sexes and geographical regions. The second part of the calculation methodology is the adjustment of nominal risk for the severity of the consequences. All calculation steps are executed separately for individual organs/tissues or a group of tissues, and the resulting values are added up to give the total radiation detriment.
(f) The calculation of nominal risk coefficients involves a number of sequential steps. They can be summarised as follows:
Baseline cancer rates were computed using cancer incidence data from selected Asian and Euro-American populations to compile rates for representative populations in different parts of the world.
Risk models were developed for cancers of nine organs/tissues, a group of other solid cancers, and leukaemia, based on the analysis of cancer incidence data, mainly from the Life Span Study of atomic bomb survivors in Hiroshima and Nagasaki. Excess relative risk (ERR) and excess absolute risk (EAR) were modelled with modifying effects of sex, age at exposure, and attained age. . For bone and skin cancers, lifetime incidence risks in Publication 60 (ICRP, 1991) were used as nominal risk estimates.
The minimum latency period was assumed to be 5 years for all cancers, including leukaemia.
The risk of exposure-induced cancer incidence (REIC) was calculated for a single exposure to 0.1 Gy, and multiplied by 10 to obtain the lifetime risk per Gy for each cancer site. It was computed for each age at exposure – 0–89 years for the whole population, and 18–64 years for the working-age population – by cumulating the risk up to the attained age of 94 years.
The weighted means of REIC for each age at exposure were used to calculate the age-averaged lifetime risk, the weight being proportional to the age distribution of the reference population.
The ERR and EAR lifetime risk estimates were averaged according to ERR:EAR weights specified for each cancer site.
The lifetime risk estimates were adjusted downward by a DDREF of 2 for solid cancers, but not for leukaemia for which a linear-quadratic model was used.
The unweighted average of the resulting values between the reference populations (males and females of Euro-American and Asian populations) provided the nominal risk for each organ or tissue.
Risks of heritable diseases were estimated separately and integrated into the above result to form a set of nominal risk coefficients.
(g) Adjustment of nominal risk for severity was performed by applying three adjustment factors that reflect lethality, quality of life, and years of life lost. These factors are virtually independent of radiation dose. Their determination was based on objective data from cancer statistics and expert judgement. The values used do not consider differences in age, sex, or between populations.
(h) Programming errors were found in the calculation of nominal risks for the working-age population in Publication 103 (ICRP, 2007). The Commission notes that these errors do not impact overall detriment values and have no implications for the System of Radiological Protection.
(i) A selected sensitivity analysis was conducted for nine solid cancers, a group of other solid cancers, and leukaemia to examine the potential impact of assumptions and parameter values in the calculation of radiation detriment. They were categorised into three groups, depending on their level of impact.
Minimal impact (change by a factor of <1.5): lifetime risk metric, minimum latency period, maximum attained age, and minimum quality-of-life factor.
Moderate impact (change by a factor of 1.5–2 for some organs or tissues): geographical coverage of the reference population, transfer model, and relative years of cancer-free life lost.
Substantial impact (change by a factor of ≥2 for some organs or tissues): sex, age at exposure, DDREF, dose assumption in the calculation of lifetime risk, and lethality fraction.
(j) The methodology for calculating radiation detriment needs to evolve to take account of advances in health care and scientific understanding of radiation effects. It will be necessary to update reference population data and to expand the geographical coverage. Assumptions for the calculation of nominal risk, including the LNT model, DDREF, and the risk transfer scheme, must be examined in the light of the latest scientific findings. Cancer risk models should be revised based on up-to-date epidemiological data. Cancer severity data require updates and refinement, including consideration of other approaches to quantify the severity of disease. It is also desirable to review the risk estimate for heritable effects, taking recent studies into account.
(k) Considering the variation of cancer risk with sex and age, it is desirable to calculate lifetime risks separately for males and females and selected ages (age groups), and average these estimates in the last stage to obtain population-averaged values. This approach makes a clear distinction between science-based risk assessment and the subsequent integration of information for radiological protection purposes, thus providing a better understanding of the construction of radiation detriment. Sex- and age-related variation should also be considered in determining the values of tissue weighting factors (wT). A detailed description of them, with different sets of relative detriments, will aid understanding of the distribution range and the representativeness of wT.
(l) There is considerable uncertainty about the shape of the dose–response curve for diseases of the circulatory system and cataracts at low doses. It is still unclear whether there is a threshold for these effects. Whether or not to include them in the calculation of radiation detriment remains an open question.
(m) Ensuring transparency and traceability of the calculation of radiation detriment is becoming increasingly important. A full description of the calculation steps is necessary, and consideration should be given to the development of open-source software to perform these calculations. It is also desirable to improve the way that radiation detriment is expressed and communicated so that non-specialists can have a balanced perspective on the health risks of radiation.
ICRP, 2022. Radiation detriment calculation methodology. ICRP Publication 152. Ann. ICRP 51(3).
Authors on behalf of ICRP
E. Cléro, L. Vaillant, W. Zhang, N. Hamada, D. Preston, D. Laurier, N. Ban
Abstract - Radiation detriment is a concept developed by the International Commission on Radiological Protection to quantify the burden of stochastic effects from low-dose and/or low-dose-rate exposures to the human population. It is determined from the lifetime risks of cancer for a set of organs and tissues and the risk of heritabl effects, taking into account the severity of the consequences. This publication provides a historical review of detriment calculation methodology since ICRP Publication 26, with details of the procedure developed in ICRP Publication 103, which clarifies data sources, risk models, computational methods, and rationale for the choice of parameter values. A selected sensitivity analysis was conducted to identify the parameters and calculation conditions that can be major sources of variation and uncertainty in the calculation of radiation detriment. It has demonstrated that sex, age at exposure, dose and dose-rate effectiveness factor, dose assumption in the calculation of lifetime risk, and lethality fraction have a substantial impact on radiation detriment values. Although the current scheme of radiation detriment calculation is well established, it needs to evolve to better reflect changes in population health statistics and progress in scientific understanding of radiation health effects. In this regard, some key parameters require updating, such as the reference population data and cancer severity. There is also room for improvement in cancer risk models based on the accumulation of recent epidemiological findings. Finally, the importance of improving the comprehensibility of the detriment concept and the transparency of its calculation process is emphasised.
© 2022 ICRP. Published by SAGE.
Keywords: Radiation detriment; Stochastic effects; Nominal risk; Sensitivity analysis.
Key Points
Radiation detriment is a concept developed by the International Commission on Radiological Protection to quantify the health impact of stochastic effects (cancer and heritable effects) from low-dose and/or low-dose-rate exposures for radiological protection purposes, considering both the probability of occurrence and the severity of these effects.
The procedure for calculating radiation detriment consists of two main parts: calculation of nominal risk (average estimate of lifetime cancer risk and risk of heritable effects associated with radiation exposure), and adjustment for severity in terms of quality of life in non-lethal conditions and length of life lost. Details of the procedure have been provided, which resolve ambiguity and correct misdescriptions, in Publication 103 (ICRP, 2007). Programming errors were found in the calculation of nominal risk for the working-age population in Publication 103. The Commission notes that these errors do not impact overall detriment and have no implications for the System of Radiological Protection.
Selected sensitivity analysis has demonstrated that sex, age at exposure, dose and dose-rate effectiveness factor, dose assumption in the calculation of lifetime risk, and lethality fraction have a substantial impact in the calculation of radiation detriment.
The calculation of radiation detriment needs to be updated to better reflect changes in reference population data and cancer severity parameters, variation of cancer risk with sex and age and between different populations, improvement in cancer risk models, and advances in risk estimation for heritable effects.
Executive Summary
(a) The concept of radiation detriment has been developed by the International Commission on Radiological Protection (hereafter, ‘the Commission’) for the purpose of radiological protection. It is defined as the excess of stochastic health effects in a group of individuals exposed to low-level radiation and their descendants compared with a non-exposed group. It is determined from sex-averaged and age-at-exposure-averaged lifetime risk estimates for a set of organs and tissues, taking into account the severity in terms of quality of life in non-lethal conditions and length of life lost.
(b) The Commission recently launched a thorough review of the System of Radiological Protection, taking into account the accumulation of practical experiences and advances in scientific understanding of radiation health effects since publication of the 2007 Recommendations (ICRP, 2007). The present publication constitutes part of this review.
(c) Radiation detriment is quantified assuming a linear-non-threshold (LNT) dose–response relationship for stochastic effects, and applying a dose and doserate effectiveness factor (DDREF) of 2 for solid cancers. This means that radiation detriment is applicable to a limited range of doses and dose rates.
(d) The values of radiation detriment should be considered not as projections of the absolute number of cases of cancer or heritable disease in a population, but as inferences based on reasonable assumptions for radiological protection.
(e) The methodology for calculating radiation detriment has developed over decades since the concept was first introduced in Publication 22 (ICRP, 1973). The most recent method in Publication 103 (ICRP, 2007) consists of two main parts. The first part is the calculation of nominal risk, which is the average estimate over age groups of the lifetime risk of cancer incidence and the risk of heritable effects associated with radiation exposure. The lifetime risk of cancer incidence is calculated for each of the reference populations (males and females of Euro-American and Asian populations), except for bone and skin cancers, and the results are averaged across sexes and geographical regions. The second part of the calculation methodology is the adjustment of nominal risk for the severity of the consequences. All calculation steps are executed separately for individual organs/tissues or a group of tissues, and the resulting values are added up to give the total radiation detriment.
(f) The calculation of nominal risk coefficients involves a number of sequential steps. They can be summarised as follows:
Baseline cancer rates were computed using cancer incidence data from selected Asian and Euro-American populations to compile rates for representative populations in different parts of the world.
Risk models were developed for cancers of nine organs/tissues, a group of other solid cancers, and leukaemia, based on the analysis of cancer incidence data, mainly from the Life Span Study of atomic bomb survivors in Hiroshima and Nagasaki. Excess relative risk (ERR) and excess absolute risk (EAR) were modelled with modifying effects of sex, age at exposure, and attained age. . For bone and skin cancers, lifetime incidence risks in Publication 60 (ICRP, 1991) were used as nominal risk estimates.
The minimum latency period was assumed to be 5 years for all cancers, including leukaemia.
The risk of exposure-induced cancer incidence (REIC) was calculated for a single exposure to 0.1 Gy, and multiplied by 10 to obtain the lifetime risk per Gy for each cancer site. It was computed for each age at exposure – 0–89 years for the whole population, and 18–64 years for the working-age population – by cumulating the risk up to the attained age of 94 years.
The weighted means of REIC for each age at exposure were used to calculate the age-averaged lifetime risk, the weight being proportional to the age distribution of the reference population.
The ERR and EAR lifetime risk estimates were averaged according to ERR:EAR weights specified for each cancer site.
The lifetime risk estimates were adjusted downward by a DDREF of 2 for solid cancers, but not for leukaemia for which a linear-quadratic model was used.
The unweighted average of the resulting values between the reference populations (males and females of Euro-American and Asian populations) provided the nominal risk for each organ or tissue.
Risks of heritable diseases were estimated separately and integrated into the above result to form a set of nominal risk coefficients.
(g) Adjustment of nominal risk for severity was performed by applying three adjustment factors that reflect lethality, quality of life, and years of life lost. These factors are virtually independent of radiation dose. Their determination was based on objective data from cancer statistics and expert judgement. The values used do not consider differences in age, sex, or between populations.
(h) Programming errors were found in the calculation of nominal risks for the working-age population in Publication 103 (ICRP, 2007). The Commission notes that these errors do not impact overall detriment values and have no implications for the System of Radiological Protection.
(i) A selected sensitivity analysis was conducted for nine solid cancers, a group of other solid cancers, and leukaemia to examine the potential impact of assumptions and parameter values in the calculation of radiation detriment. They were categorised into three groups, depending on their level of impact.
Minimal impact (change by a factor of <1.5): lifetime risk metric, minimum latency period, maximum attained age, and minimum quality-of-life factor.
Moderate impact (change by a factor of 1.5–2 for some organs or tissues): geographical coverage of the reference population, transfer model, and relative years of cancer-free life lost.
Substantial impact (change by a factor of ≥2 for some organs or tissues): sex, age at exposure, DDREF, dose assumption in the calculation of lifetime risk, and lethality fraction.
(j) The methodology for calculating radiation detriment needs to evolve to take account of advances in health care and scientific understanding of radiation effects. It will be necessary to update reference population data and to expand the geographical coverage. Assumptions for the calculation of nominal risk, including the LNT model, DDREF, and the risk transfer scheme, must be examined in the light of the latest scientific findings. Cancer risk models should be revised based on up-to-date epidemiological data. Cancer severity data require updates and refinement, including consideration of other approaches to quantify the severity of disease. It is also desirable to review the risk estimate for heritable effects, taking recent studies into account.
(k) Considering the variation of cancer risk with sex and age, it is desirable to calculate lifetime risks separately for males and females and selected ages (age groups), and average these estimates in the last stage to obtain population-averaged values. This approach makes a clear distinction between science-based risk assessment and the subsequent integration of information for radiological protection purposes, thus providing a better understanding of the construction of radiation detriment. Sex- and age-related variation should also be considered in determining the values of tissue weighting factors (wT). A detailed description of them, with different sets of relative detriments, will aid understanding of the distribution range and the representativeness of wT.
(l) There is considerable uncertainty about the shape of the dose–response curve for diseases of the circulatory system and cataracts at low doses. It is still unclear whether there is a threshold for these effects. Whether or not to include them in the calculation of radiation detriment remains an open question.
(m) Ensuring transparency and traceability of the calculation of radiation detriment is becoming increasingly important. A full description of the calculation steps is necessary, and consideration should be given to the development of open-source software to perform these calculations. It is also desirable to improve the way that radiation detriment is expressed and communicated so that non-specialists can have a balanced perspective on the health risks of radiation.
