Recommended citation
ICRP, 2021. Use of dose quantities in radiological protection. ICRP Publication 147. Ann. ICRP 50(1).
Authors on behalf of ICRP
J.D. Harrison, M. Balonov, F. Bochud, C. Martin, H-G. Menzel, P. Ortiz-Lopez, R. Smith-Bindman, J.R. Simmonds, R. Wakeford
Abstract - The central dose quantities used in radiological protection are absorbed dose, equivalent dose, and effective dose. The concept of effective dose was developed by the International Commission on Radiological Protection (ICRP) as a riskadjusted dosimetric quantity for the management of protection against stochastic effects, principally cancer, enabling comparison of estimated doses with dose limits, dose constraints, and reference levels expressed in the same quantity. Its use allows all radiation exposures from external and internal sources to be considered together and summed, relying on the assumptions of a linear non-threshold dose–response relationship, equivalence of acute and chronic exposures at low doses or low dose rates, and equivalence of external and internal exposures. ICRP Publication 103 provides detailed explanation of the purpose and use of effective dose and equivalent dose to individual organs and tissues. This publication provides further guidance on the scientific basis for the control of radiation risks using dose quantities, and discusses occupational, public, and medical applications. It is recognised that best estimates of risk to individuals will use organ/tissue doses and specific dose risk models. Although doses incurred at low levels of exposure may be measured or assessed with reasonable accuracy, the associated risks are increasingly uncertain at lower doses. Bearing in mind the uncertainties associated with risk projection to low doses or low dose rates, it is concluded that effective dose may be considered as an approximate indicator of possible risk, recognising also that lifetime cancer risks vary with age at exposure, sex, and population group. A further conclusion is that equivalent dose is not required as a protection quantity. It will be more appropriate for limits for the avoidance of tissue reactions for the skin, hands and feet, and lens of the eye to be set in terms of absorbed dose rather than equivalent dose.
© 2021 ICRP. Published by SAGE.
Keywords: Absorbed dose; Equivalent dose; Effective dose; Stochastic risks; Tissue reactions; Occupational, public, and medical exposures.
Key Points
The purpose of this publication is to consolidate and expand the explanations provided in Publication 103 (ICRP, 2007a), but also to clarify the use of dose quantities in relation to risks to health, reaching conclusions that go beyond the advice given in Publication 103.
Effective dose and collective effective dose are valuable tools for use in the optimisation of protection against stochastic effects, principally cancer, for occupational and public exposures. . Effective dose is used in medicine for comparing doses from different medical procedures, informing judgements on justification, and establishing constraints for carers and volunteers in medical research. Where doses from the same technique are being compared, measurable quantities are preferred.
Effective dose will generally be used at doses below 100 mSv, but its use at acute doses in the range up to approximately 1 Sv is reasonable, noting the possibility of occurrence of tissue reactions, particularly from non-uniform distribution of dose.
Bearing in mind the uncertainties associated with risk projection to low doses or low dose rates, effective dose may be considered as an approximate indicator of possible risk, recognising that lifetime cancer risks vary with age at exposure, sex, and population group. It is emphasised that use of effective dose in this way is not a substitute for specific risk analysis for individual cancer types using organ/tissue doses.
The use of collective effective dose to predict potential/possible health effects should be treated with caution, put into context, and judged in relation to background morbidity rates.
Absorbed dose is the most appropriate quantity for use in setting limits on organ/ tissue doses to prevent tissue reactions (deterministic effects). The Commission expects to change from the use of equivalent dose to set limits on organ/tissue doses at the time that new general recommendations are issued.
Executive Summary
(a) The dosimetric quantities used in radiological protection are absorbed dose [with the unit of gray (Gy)], equivalent dose, and effective dose [both with the unit of sievert (Sv)]; the base unit is J kg-1in each case. Absorbed dose is calculated for protection purposes as an average over organs and tissues, and is the primary scientific quantity from which effective dose is calculated. Absorbed dose is the most appropriate quantity for use in setting limits on organ/tissue doses to prevent tissue reactions (deterministic effects). Equivalent dose is an intermediate quantity in the calculation of effective dose, and the radiation weighting factors (wR) applied to absorbed doses and used in the calculation of equivalent dose relate to stochastic effects at low levels of exposure rather than tissue reactions. The Commission considers that the use of equivalent dose to set limits on organ/tissue doses to prevent tissue reactions should be discontinued, but that current limits can continue to be applied until new general recommendations are issued. Radiation weighting for tissue reactions will require further consideration.
(b) Effective dose is calculated as the weighted average of organ/tissue equivalent doses, summing equivalent doses multiplied by tissue weighting factors (wT) which provide a simplified representation of fractional contributions to total stochastic detriment from cancer and heritable effects. Detriment-adjusted nominal risk coefficients (Sv-1) are calculated as averages from sex-, age-, and population-specific values to provide internationally applicable coefficients for all workers (18–64 years of age at exposure) and the whole population (0–84 years of age at exposure). Effective dose is accepted internationally as the central radiological protection quantity, providing a risk-adjusted measure of total body dose from external and internal sources in relation to risks of cancer and heritable effects. It has proved to be a valuable and robust quantity for use in the optimisation of protection for workers and members of the public, the setting of control criteria (constraints, reference levels, and limits), and the demonstration of compliance. Its use requires the assumption of a linear non-threshold dose–response relationship between dose and risk at low doses or low dose rates, the equivalence of effect of acute and chronic low-level exposures, and the equivalence of effect of internal and external exposures. Although effective dose is most commonly used at doses below 100 mSv, its use in emergency exposure situations at acute doses in the range up to approximately 1 Sv is reasonable. However, it should be noted that in addition to the increased risk of stochastic effects at higher doses, the possibility of occurrence of tissue reactions should also be considered at such doses, particularly if a significant contribution is made by nonuniform distribution of absorbed dose from external sources or from radionuclides concentrated in specific tissues/organs.
(c) Effective dose is calculated for sex-averaged Reference Persons of specified ages. The Publication 103 (ICRP, 2007a) definition of effective dose includes the specification of Reference Male and Female anatomical models for radiation transport calculations. While exposures may relate to individuals or population groups, effective dose is calculated for Reference Persons exposed in a defined way. The Commission provides effective dose coefficients for situations of external and internal exposures of workers and members of the public, and for radiopharmaceutical administrations to patients, as reference coefficients for use in prospective and retrospective dose assessments. Reference dose coefficients are provided for particular circumstances of exposure, including specific chemical and physical forms of ingested and inhaled radionuclides. Site-specific information on the exposure should be used if available and if the level of exposure warrants more precise estimation of dose.
(d) In evaluating annual exposures, effective dose is calculated as the sum of external dose received in the year and committed dose from internal exposures during the year, where committed dose is integrated over a 50-year period for adults and up to 70 years of age for children. This procedure introduces an element of conservatism for long-lived radionuclides with long biological half-times, but for many radionuclides, all or most of the dose is delivered in the first year after intake. Although effective dose coefficients are provided for a number of paediatric age groups, it is normally sufficient in public dose assessments to consider the age groups of 1 year and 10 years, together with adults. Effective dose coefficients for the fetus following intakes of radionuclides are provided for comparison with dose for other age groups, showing that it is only in the case of a few radionuclides that fetal doses may need to be considered.
(e) While age-, sex-, and population-related differences in risks per Gy are recognised, the use of constraints, reference levels, and limits expressed in effective dose and applied to all workers and all members of the public, together with optimisation, provides a pragmatic, equitable, and workable system of protection that does not distinguish on an individual basis. A distinction should be drawn between the use of scientific information to construct a workable and acceptable protection system and the provision of best scientific estimates of dose and risk to individuals and specific population groups.
(f) In medical applications, estimates of effective dose can be used for comparing doses from different diagnostic and interventional imaging modalities (e.g. computed tomography and nuclear medicine) and exposure techniques that give different spatial distributions of radiation within the body tissues. In this context, effective dose is used to provide a generic indicator for classifying different types of medical procedure into broad risk categories for the purpose of communicating risks to clinicians and patients. Effective dose is also used to inform decisions on justification of patient diagnostic and interventional procedures, planning requirements in research studies, and evaluation of unintended exposures. In each of these cases, effective dose provides an approximate measure of possible detriment. Thus, effective dose can be used prospectively as an indicator of radiation detriment in justification decisions and when planning medical research studies involving radiation exposure, or retrospectively in assessments of accidental exposures. However, measurable quantities are used directly in applications comparing doses from particular procedures in different health centres, including the setting of diagnostic reference levels and in maintenance of patient records.
(g) Bearing in mind the uncertainties associated with risk projection to low doses or low dose rates, effective dose may be considered as an approximate indicator of possible risk, recognising also that lifetime cancer risk varies with age at exposure, sex, and population group. For medical procedures or other situations in which a single organ receives the majority of the dose, such as the breast in mammography or the thyroid from therapeutic administration of radioiodine, mean absorbed doses to the tissues of interest should be used rather than effective dose. In considering doses to patients with diseases with poor prognoses, life expectancy will be a consideration in evaluating radiation risks. The use of effective dose as an approximate indicator of possible risk is not a substitute for a risk analysis using best estimates of organ/tissue doses; appropriate information on the relative effectiveness of different radiation types; and age-, sex-, and population-specific risk factors, with consideration of uncertainties.
(h) Collective effective dose is a valuable tool in the optimisation of protection of workers and the public. It can be used, together with the distribution of individual doses, to inform decisions on the optimum balance between relatively large exposures of a few workers and smaller exposures of a larger number of workers. For public exposures, it can be used as part of the optimisation process for planned, existing, and emergency exposure situations. For occupational, public, and medical exposures, it has been used in comparisons of exposure levels in different countries and changes in dose levels with time (e.g. UNSCEAR, 2008; NCRP, 2019). Its use to predict potential/possible health effects may be useful in particular circumstances – for example, to inform judgements on the need for medical or epidemiological follow-up – but should be treated with caution and judged in relation to background morbidity rates, with consideration of the distribution of doses in time and space, and uncertainties in dose and risk estimation. The computation of numbers of cases of cancer based on collective effective doses involving extremely low exposures to very large populations should be avoided. Due to the large uncertainties associated with such estimates, the results will be more misleading than informative. The Commission has given advice on the use of collective dose as a tool for optimisation of protection in Publication 101 (ICRP, 2006), taking account of the need to disaggregate doses when necessary to allow separate consideration of homogenous parts of the dose distribution in time and space.
ICRP, 2021. Use of dose quantities in radiological protection. ICRP Publication 147. Ann. ICRP 50(1).
Authors on behalf of ICRP
J.D. Harrison, M. Balonov, F. Bochud, C. Martin, H-G. Menzel, P. Ortiz-Lopez, R. Smith-Bindman, J.R. Simmonds, R. Wakeford
Abstract - The central dose quantities used in radiological protection are absorbed dose, equivalent dose, and effective dose. The concept of effective dose was developed by the International Commission on Radiological Protection (ICRP) as a riskadjusted dosimetric quantity for the management of protection against stochastic effects, principally cancer, enabling comparison of estimated doses with dose limits, dose constraints, and reference levels expressed in the same quantity. Its use allows all radiation exposures from external and internal sources to be considered together and summed, relying on the assumptions of a linear non-threshold dose–response relationship, equivalence of acute and chronic exposures at low doses or low dose rates, and equivalence of external and internal exposures. ICRP Publication 103 provides detailed explanation of the purpose and use of effective dose and equivalent dose to individual organs and tissues. This publication provides further guidance on the scientific basis for the control of radiation risks using dose quantities, and discusses occupational, public, and medical applications. It is recognised that best estimates of risk to individuals will use organ/tissue doses and specific dose risk models. Although doses incurred at low levels of exposure may be measured or assessed with reasonable accuracy, the associated risks are increasingly uncertain at lower doses. Bearing in mind the uncertainties associated with risk projection to low doses or low dose rates, it is concluded that effective dose may be considered as an approximate indicator of possible risk, recognising also that lifetime cancer risks vary with age at exposure, sex, and population group. A further conclusion is that equivalent dose is not required as a protection quantity. It will be more appropriate for limits for the avoidance of tissue reactions for the skin, hands and feet, and lens of the eye to be set in terms of absorbed dose rather than equivalent dose.
© 2021 ICRP. Published by SAGE.
Keywords: Absorbed dose; Equivalent dose; Effective dose; Stochastic risks; Tissue reactions; Occupational, public, and medical exposures.
Key Points
The purpose of this publication is to consolidate and expand the explanations provided in Publication 103 (ICRP, 2007a), but also to clarify the use of dose quantities in relation to risks to health, reaching conclusions that go beyond the advice given in Publication 103.
Effective dose and collective effective dose are valuable tools for use in the optimisation of protection against stochastic effects, principally cancer, for occupational and public exposures. . Effective dose is used in medicine for comparing doses from different medical procedures, informing judgements on justification, and establishing constraints for carers and volunteers in medical research. Where doses from the same technique are being compared, measurable quantities are preferred.
Effective dose will generally be used at doses below 100 mSv, but its use at acute doses in the range up to approximately 1 Sv is reasonable, noting the possibility of occurrence of tissue reactions, particularly from non-uniform distribution of dose.
Bearing in mind the uncertainties associated with risk projection to low doses or low dose rates, effective dose may be considered as an approximate indicator of possible risk, recognising that lifetime cancer risks vary with age at exposure, sex, and population group. It is emphasised that use of effective dose in this way is not a substitute for specific risk analysis for individual cancer types using organ/tissue doses.
The use of collective effective dose to predict potential/possible health effects should be treated with caution, put into context, and judged in relation to background morbidity rates.
Absorbed dose is the most appropriate quantity for use in setting limits on organ/ tissue doses to prevent tissue reactions (deterministic effects). The Commission expects to change from the use of equivalent dose to set limits on organ/tissue doses at the time that new general recommendations are issued.
Executive Summary
(a) The dosimetric quantities used in radiological protection are absorbed dose [with the unit of gray (Gy)], equivalent dose, and effective dose [both with the unit of sievert (Sv)]; the base unit is J kg-1in each case. Absorbed dose is calculated for protection purposes as an average over organs and tissues, and is the primary scientific quantity from which effective dose is calculated. Absorbed dose is the most appropriate quantity for use in setting limits on organ/tissue doses to prevent tissue reactions (deterministic effects). Equivalent dose is an intermediate quantity in the calculation of effective dose, and the radiation weighting factors (wR) applied to absorbed doses and used in the calculation of equivalent dose relate to stochastic effects at low levels of exposure rather than tissue reactions. The Commission considers that the use of equivalent dose to set limits on organ/tissue doses to prevent tissue reactions should be discontinued, but that current limits can continue to be applied until new general recommendations are issued. Radiation weighting for tissue reactions will require further consideration.
(b) Effective dose is calculated as the weighted average of organ/tissue equivalent doses, summing equivalent doses multiplied by tissue weighting factors (wT) which provide a simplified representation of fractional contributions to total stochastic detriment from cancer and heritable effects. Detriment-adjusted nominal risk coefficients (Sv-1) are calculated as averages from sex-, age-, and population-specific values to provide internationally applicable coefficients for all workers (18–64 years of age at exposure) and the whole population (0–84 years of age at exposure). Effective dose is accepted internationally as the central radiological protection quantity, providing a risk-adjusted measure of total body dose from external and internal sources in relation to risks of cancer and heritable effects. It has proved to be a valuable and robust quantity for use in the optimisation of protection for workers and members of the public, the setting of control criteria (constraints, reference levels, and limits), and the demonstration of compliance. Its use requires the assumption of a linear non-threshold dose–response relationship between dose and risk at low doses or low dose rates, the equivalence of effect of acute and chronic low-level exposures, and the equivalence of effect of internal and external exposures. Although effective dose is most commonly used at doses below 100 mSv, its use in emergency exposure situations at acute doses in the range up to approximately 1 Sv is reasonable. However, it should be noted that in addition to the increased risk of stochastic effects at higher doses, the possibility of occurrence of tissue reactions should also be considered at such doses, particularly if a significant contribution is made by nonuniform distribution of absorbed dose from external sources or from radionuclides concentrated in specific tissues/organs.
(c) Effective dose is calculated for sex-averaged Reference Persons of specified ages. The Publication 103 (ICRP, 2007a) definition of effective dose includes the specification of Reference Male and Female anatomical models for radiation transport calculations. While exposures may relate to individuals or population groups, effective dose is calculated for Reference Persons exposed in a defined way. The Commission provides effective dose coefficients for situations of external and internal exposures of workers and members of the public, and for radiopharmaceutical administrations to patients, as reference coefficients for use in prospective and retrospective dose assessments. Reference dose coefficients are provided for particular circumstances of exposure, including specific chemical and physical forms of ingested and inhaled radionuclides. Site-specific information on the exposure should be used if available and if the level of exposure warrants more precise estimation of dose.
(d) In evaluating annual exposures, effective dose is calculated as the sum of external dose received in the year and committed dose from internal exposures during the year, where committed dose is integrated over a 50-year period for adults and up to 70 years of age for children. This procedure introduces an element of conservatism for long-lived radionuclides with long biological half-times, but for many radionuclides, all or most of the dose is delivered in the first year after intake. Although effective dose coefficients are provided for a number of paediatric age groups, it is normally sufficient in public dose assessments to consider the age groups of 1 year and 10 years, together with adults. Effective dose coefficients for the fetus following intakes of radionuclides are provided for comparison with dose for other age groups, showing that it is only in the case of a few radionuclides that fetal doses may need to be considered.
(e) While age-, sex-, and population-related differences in risks per Gy are recognised, the use of constraints, reference levels, and limits expressed in effective dose and applied to all workers and all members of the public, together with optimisation, provides a pragmatic, equitable, and workable system of protection that does not distinguish on an individual basis. A distinction should be drawn between the use of scientific information to construct a workable and acceptable protection system and the provision of best scientific estimates of dose and risk to individuals and specific population groups.
(f) In medical applications, estimates of effective dose can be used for comparing doses from different diagnostic and interventional imaging modalities (e.g. computed tomography and nuclear medicine) and exposure techniques that give different spatial distributions of radiation within the body tissues. In this context, effective dose is used to provide a generic indicator for classifying different types of medical procedure into broad risk categories for the purpose of communicating risks to clinicians and patients. Effective dose is also used to inform decisions on justification of patient diagnostic and interventional procedures, planning requirements in research studies, and evaluation of unintended exposures. In each of these cases, effective dose provides an approximate measure of possible detriment. Thus, effective dose can be used prospectively as an indicator of radiation detriment in justification decisions and when planning medical research studies involving radiation exposure, or retrospectively in assessments of accidental exposures. However, measurable quantities are used directly in applications comparing doses from particular procedures in different health centres, including the setting of diagnostic reference levels and in maintenance of patient records.
(g) Bearing in mind the uncertainties associated with risk projection to low doses or low dose rates, effective dose may be considered as an approximate indicator of possible risk, recognising also that lifetime cancer risk varies with age at exposure, sex, and population group. For medical procedures or other situations in which a single organ receives the majority of the dose, such as the breast in mammography or the thyroid from therapeutic administration of radioiodine, mean absorbed doses to the tissues of interest should be used rather than effective dose. In considering doses to patients with diseases with poor prognoses, life expectancy will be a consideration in evaluating radiation risks. The use of effective dose as an approximate indicator of possible risk is not a substitute for a risk analysis using best estimates of organ/tissue doses; appropriate information on the relative effectiveness of different radiation types; and age-, sex-, and population-specific risk factors, with consideration of uncertainties.
(h) Collective effective dose is a valuable tool in the optimisation of protection of workers and the public. It can be used, together with the distribution of individual doses, to inform decisions on the optimum balance between relatively large exposures of a few workers and smaller exposures of a larger number of workers. For public exposures, it can be used as part of the optimisation process for planned, existing, and emergency exposure situations. For occupational, public, and medical exposures, it has been used in comparisons of exposure levels in different countries and changes in dose levels with time (e.g. UNSCEAR, 2008; NCRP, 2019). Its use to predict potential/possible health effects may be useful in particular circumstances – for example, to inform judgements on the need for medical or epidemiological follow-up – but should be treated with caution and judged in relation to background morbidity rates, with consideration of the distribution of doses in time and space, and uncertainties in dose and risk estimation. The computation of numbers of cases of cancer based on collective effective doses involving extremely low exposures to very large populations should be avoided. Due to the large uncertainties associated with such estimates, the results will be more misleading than informative. The Commission has given advice on the use of collective dose as a tool for optimisation of protection in Publication 101 (ICRP, 2006), taking account of the need to disaggregate doses when necessary to allow separate consideration of homogenous parts of the dose distribution in time and space.
