The use of dose quantities in radiological protection: ICRP publication 147 Ann ICRP 50(1) 2021.

The International Commission on Radiological Protection has recently published a report (ICRP Publication 147;Ann. ICRP50, 2021) on the use of dose quantities in radiological protection, under the same authorship as this Memorandum. Here, we present a brief summary of the main elements of the report. ICRP Publication 147 consolidates and clarifies the explanations provided in the 2007 ICRP Recommendations (Publication 103) but reaches conclusions that go beyond those presented in Publication 103. Further guidance is provided on the scientific basis for the control of radiation risks using dose quantities in occupational, public and medical applications. It is emphasised that best estimates of risk to individuals will use organ/tissue absorbed doses, appropriate relative biological effectiveness factors and dose-risk models for specific health effects. However, bearing in mind uncertainties including those associated with risk projection to low doses or low dose rates, it is concluded that in the context of radiological protection, effective dose may be considered as an approximate indicator of possible risk of stochastic health effects following low-level exposure to ionising radiation. In this respect, it should also be recognised that lifetime cancer risks vary with age at exposure, sex and population group. The ICRP report also concludes that equivalent dose is not needed as a protection quantity. Dose limits for the avoidance of tissue reactions for the skin, hands and feet, and lens of the eye will be more appropriately set in terms of absorbed dose rather than equivalent dose.

Optimisation of environmental remediation: how to select and use the reference levels.

A number of past industrial activities and accidents have resulted in the radioactive contamination of large areas at many sites around the world, giving rise to a need for remediation. According to the International Commission on Radiological Protection (ICRP) and International Atomic Energy Agency (IAEA), such situations should be managed as existing exposure situations (ExESs). Control of exposure to the public in ExESs is based on the application of appropriate reference levels (RLs) for residual doses. The implementation of this potentially fruitful concept for the optimisation of remediation in various regions is hampered by a lack of practical experience and relevant guidance. This paper suggests a generic methodology for the selection of numeric values of relevant RLs both in terms of residual annual effective dose and derived RLs (DRLs) based on an appropriate dose assessment. The value for an RL should be selected in the range of the annual residual effective dose of 1-20 mSv, depending on the prevailing circumstances for the exposure under consideration. Within this range, RL values should be chosen by the following assessment steps: (a) assessment of the projected dose, i.e. the dose to a representative person without remedial actions by means of a realistic model as opposed to a conservative model; (b) modelling of the residual dose to a representative person following application of feasible remedial actions; and (c) selection of an RL value between the projected and residual doses, taking account of the prevailing social and economic conditions. This paper also contains some recommendations for practical implementation of the selected RLs for the optimisation of public protection. The suggested methodology used for the selection of RLs (in terms of dose) and the calculation of DRLs (in terms of activity concentration in food, ambient dose rate, etc) has been illustrated by a retrospective analysis of post-Chernobyl monitoring and modelling data from the Bryansk region, Russia, 2001. From this example, it follows that analysis of real data leads to the selection of an RL from a relatively narrow annual dose range (in this case, about 2-3 mSv), from which relevant DRLs can be calculated and directly used for optimisation of the remediation programme.

Harmonisation of standards for permissible radionuclide activity concentrations in foodstuffs in the long term after the Chernobyl accident.

The article critically examines the practice of post-Chernobyl standardisation of radionuclide concentrations (mainly 137Cs and 90Sr) in food products (FPs) in the USSR and the successor countries of Belarus, Russia and Ukraine. Recommendations are given on potential harmonisation of these standards of radionuclide concentrations in FPs among the three countries, taking into account substantial international experience. We propose to reduce the number of product groups for standardisation purposes from the current amount of several dozens to three to five groups to optimise radiation control and increase the transparency of the process. We recommend five product groups for the standardisation of 137Cs and three groups for 90Sr in food in radiocontaminated areas. The values of standards for individual product groups are recommended to be set proportionally to the measured specific activity in each of these groups, which will reduce unreasonable food rejection. The standards might be set for the entire country, and could be also used to control imports from other countries as well as exports to other countries. The developed recommendations were transferred in 2015-2016 to the regulatory authorities of the three countries.

Patient doses from medical examinations in Russia: 2009-2015.

The aim of this study was to evaluate adult patient doses in Russia in the context of patient protection. Effective doses from x-ray and nuclear medicine examinations were assessed using two approaches. The first was based on data collection performed by the authors in hospitals in St. Petersburg and other 17 Russian regions. The second approach was to assess mean doses through the collective dose estimated annually within the federal data bank ESKID. In 2015, 203 million examinations were conducted in Russia, i.e. 1.4 examinations per capita. The number of examinations has increased by 35% over the last 10 years. Patient doses from x-ray examinations are strongly dependent on the imaging modality. Mean dose increases by an order of magnitude with each x-ray modality from dental examinations (0.01-0.1 mSv) to radiography (0.1-1 mSv), fluoroscopy and CT (1-10 mSv) and to interventional examinations (more than 10 mSv). Mean doses for x-ray examinations are comparable with that of foreign countries. Scintigraphy examinations with 99mTc are associated with mean doses of 1-5 mSv. Mean doses from PET/CT whole body examinations are 15-25 mSv with similar contributions from CT and radiopharmaceuticals. In nuclear medicine, patient doses are lower compared to other countries. According to ESKID data the collective dose from medical exposure in Russia has decreased from 140 000 man-Sv in 2000 to 77 000 man-Sv in 2015. Medical exposure contributes about 13% into a total collective dose. The maximum contribution was from CT examinations, i.e. 45% in 2015. A range of mean doses between different hospitals was up to two orders of magnitude for radiography and one order of magnitude for CT. In interventional studies, the scatter of individual doses was significant. Significant variations in doses between hospitals and some regions indicate the potential for optimization with the focus on interventional examinations, CT and nuclear medicine examinations combined with CT.

PROPOSALS FOR THE ESTABLISHMENT OF NATIONAL DIAGNOSTIC REFERENCE LEVELS FOR RADIOGRAPHY FOR ADULT PATIENTS BASED ON REGIONAL DOSE SURVEYS IN RUSSIAN FEDERATION.

In 2009-2014, dose surveys aimed to collect adult patient data and parameters of most common radiographic examinations were performed in six Russian regions. Typical patient doses were estimated for the selected examinations both in entrance surface dose and in effective dose. 75%-percentiles of typical patient effective dose distributions were proposed as preliminary regional diagnostic reference levels (DRLs) for radiography. Differences between the 75%-percentiles of regional typical patient dose distributions did not exceed 30-50% for the examinations with standardized clinical protocols (skull, chest and thoracic spine) and a factor of 1.5 for other examinations. Two different approaches for establishing national DRLs were evaluated: as a 75%-percentile of a pooled regional sample of patient typical doses (pooled method) and as a median of 75%-percentiles of regional typical patient dose distributions (median method). Differences between pooled and median methods for effective dose did not exceed 20%. It was proposed to establish Russian national DRLs in effective dose using a pooled method. In addition, the local authorities were granted an opportunity to establish regional DRLs if the local radiological practice and typical patient dose distributions are significantly different.

Use of effective dose.

International Commission on Radiological Protection (ICRP) Publication 103 provided a detailed explanation of the purpose and use of effective dose and equivalent dose to individual organs and tissues. Effective dose has proven to be a valuable and robust quantity for use in the implementation of protection principles. However, questions have arisen regarding practical applications, and a Task Group has been set up to consider issues of concern. This paper focusses on two key proposals developed by the Task Group that are under consideration by ICRP: (1) confusion will be avoided if equivalent dose is no longer used as a protection quantity, but regarded as an intermediate step in the calculation of effective dose. It would be more appropriate for limits for the avoidance of deterministic effects to the hands and feet, lens of the eye, and skin, to be set in terms of the quantity, absorbed dose (Gy) rather than equivalent dose (Sv). (2) Effective dose is in widespread use in medical practice as a measure of risk, thereby going beyond its intended purpose. While doses incurred at low levels of exposure may be measured or assessed with reasonable reliability, health effects have not been demonstrated reliably at such levels but are inferred. However, bearing in mind the uncertainties associated with risk projection to low doses or low dose rates, it may be considered reasonable to use effective dose as a rough indicator of possible risk, with the additional consideration of variation in risk with age, sex and population group.

Nuclear medicine examinations of children in Russia.

The number and specification of radionuclide examinations, administrated activity and effective doses were collected during 2011-13 for 4944 paediatric patients from 10 nuclear medicine (NM) departments of some Russian regions. The kidney examinations account for about 70 % of paediatric NM examinations in general hospitals. Diagnostics of all other organs contribute from 2 to 8 % each in the total number of paediatric examinations. Administrated activities of radiopharmaceuticals are approximately proportional to the child's age, and variations between different hospitals usually are within the factor of 3-4 and for some types of examination up to 10. The range of the effective dose due to paediatric NM examinations is roughly estimated as 2-6 mSv per examination, approximately the same as in adults. Some examinations (heart, thyroid, whole body) result in doses of younger children that are 2-3 times higher than the doses of adults. Effective doses in paediatric positron emission tomography (PET) diagnostics are in the range of 4-10 mSv per examination and are higher compared with the dose of adult patients. The application of combined radiodiagnostic technologies (single photon emission computer tomography with roentghen computer tomography [SPECT/CT] or PET with roetghen computer tomography [PET/CT]) increases the effective dose of patients by the factor of 1.5-2 for the skeleton or whole body examinations.

Russian practical guidance on radiological support for justification of X-ray and nuclear medicine examinations.

An important part of the justification process is assessment of the radiation risks caused by exposure of a patient during examination. The authors developed official national methodology both for medical doctors and sanitary inspectors called 'assessment of radiation risks of patients undergoing diagnostic examinations with the use of ionizing radiation'. The document addresses patients of various age groups and a wide spectrum of modern X-ray and nuclear medicine examinations. International scale of risk categorisation was implemented by the use of effective dose with account for age dependence of radiation risk. The survey of effective doses in radiology, including CT, mammography, and intervention radiology, and nuclear medicine, including single-photon emission tomography and positron emission tomography, for patients of various age groups from several regions of Russia was used for the risk assessment. The output of the methodology is a series of tables for each diagnostic technology with lists of examinations for three age groups (children/adolescents, adults and seniors) corresponding to various radiation risk categories.

Effective dose and risks from medical X-ray procedures.

The radiation risks from a range of medical x-ray examinations (radiography, fluoroscopy, and computed tomography) were assessed as a function of the age and sex of the patient using risk models described in Publication 103 (ICRP, 2007) and UNSCEAR (2006, Annex A). Such estimates of risk based on typical organ doses were compared with those derived from effective doses using the International Commission on Radiological Protection's nominal risk coefficients. Methodologically similar but not identical dose and risk calculations were performed independently at the Institute of Radiation Hygiene (Russia) and the Health Protection Agency (UK), and led to similar conclusions. The radiogenic risk of stochastic health effects following various x-ray procedures varied significantly with the patient's age and sex, but to differing degrees depending on which body organs were irradiated. In general, the risks of radiation-induced stochastic health effects in children are estimated to be higher (by a factor of ≤ 4) than in adults, and risks in senior patients are lower by a factor of ≥ 10 relative to younger people. If risks are assessed on the basis of effective dose, they are underestimated for children of both sexes by a factor of ≤ 4. This approach overestimates risks by a factor of ≤ 3 for adults and about an order of magnitude for senior patients. The significant sex and age dependence of radiogenic risk for different cancer types is an important consideration for radiologists when planning x-ray examinations. Whereas effective dose was not intended to provide a measure of risk associated with such examinations, it may be sufficient to make simple adjustments to the nominal risk per unit effective dose to account for age and sex differences.

On protecting the inexperienced reader from Chernobyl myths.

The health and environmental consequences of the Chernobyl accident continue to attract the attention of experts, decision-makers and the general public, and now these consequences have been given added relevance by the similar accident in 2011 at the Fukushima-1 nuclear power plant (NPP) in Japan. Expert analysis of radiation levels and effects has been conducted by international bodies--UNSCEAR in 2008 and the Chernobyl Forum during 2003-5. At the same time, three Russian and Belarusian scientists, Yablokov, Nesterenko and Nesterenko (2009 Chernobyl. Consequences of the Catastrophe for People and the Environment (New York: Annals of the New York Academy of Sciences)) published both in Russian and English a substantial review of the consequences of Chernobyl based mostly on Russian-language papers. In this book, they suggested a departure from analytical epidemiological studies in favour of ecological ones. This erroneous approach resulted in the overestimation of the number of accident victims by more than 800 000 deaths during 1987-2004. This paper investigates the mistakes in methodology made by Yablokov et al and concludes that these errors led to a clear exaggeration of radiation-induced health effects. Should similar mistakes be made following the 2011 accident at Fukushima-1 NPP this could lead quite unnecessarily to a panic reaction by the public about possible health effects and to erroneous decisions by the authorities in Japan.

Release criteria for patients having undergone radionuclide therapy and criteria for their crossing the state border of the Russian Federation.

By means of a conservative dosimetry model, the values of operational radiological criteria for patients released from hospital--residual activity in a body and dose rate near the patient's body--are substantiated based on the effective dose limit of 5 mSv for persons helping the patient or living with him and 1 mSv for other adults and children. Two sets of operative criteria for radionuclides (125)I, (131)I, (153)Sm and (188)Re used in Russia for radionuclide therapy were derived. Release criteria for (125)I well differ from such values in other countries because in this work absorption of (125)I low-energy photon radiation in the patient was taken into account. When a patient having undergone radionuclide therapy crosses the frontier of Russia, high-sensitivity devices for radiation control at the custom can detect the patient. A simplified radiological assessment of the patient was suggested aimed at provision of radiation safety for patient companions in transport.

Contribution of internal exposures to the radiological consequences of the Chernobyl accident.

The main pathways leading to exposure of members of the general public due to the Chernobyl accident were external exposure from radionuclides deposited on the ground and ingestion of contaminated terrestrial food products. The collective dose to the thyroid was nearly 1.5 million man Gy in Belarus, Russia and Ukraine with nearly half received by children and adolescents. The collective effective dose received in 1986-2005 by approximately five million residents living in the affected areas of the three countries was approximately 50,000 man Sv with approximately 40% from ingestion. That contribution might have been larger if countermeasures had not been applied. The main radionuclide contributing to both external and internal effective dose is 137Cs with smaller contributions of 134Cs and 90Sr and negligible contribution of transuranic elements. The major demonstrated radiation-caused health effect of the Chernobyl accident has been an elevated incidence of thyroid cancer in children.

Inter-comparison of absorbed dose rates for non-human biota.

A number of approaches have been proposed to estimate the exposure of non-human biota to ionizing radiation. This paper reports an inter-comparison of the unweighted absorbed dose rates for the whole organism (compared as dose conversion coefficients, or DCCs) for both internal and external exposure, estimated by 11 of these approaches for selected organisms from the Reference Animals and Plants geometries as proposed by the International Commission on Radiological Protection. Inter-comparison results indicate that DCCs for internal exposure compare well between the different approaches, whereas variation is greater for external exposure DCCs. Where variation among internal DCCs is greatest, it is generally due to different daughter products being included in the DCC of the parent. In the case of external exposures, particularly to low-energy beta-emitters, variations are most likely to be due to different media densities being assumed. On a radionuclide-by-radionuclide basis, the different approaches tend to compare least favourably for (3)H, (14)C and the alpha-emitters. This is consistent with models with different source/target geometry assumptions showing maximum variability in output for the types of radiation having the lowest range across matter. The intercomparison demonstrated that all participating approaches to biota dose calculation are reasonably comparable, despite a range of different assumptions being made.

The Chernobyl Forum: major findings and recommendations.

The accident at the Chernobyl NPP in 1986 was the most severe in the history of the nuclear industry, causing a huge release of radionuclides over large areas of Europe. The recently completed Chernobyl Forum concluded that after a number of years, along with reduction of radiation levels and accumulation of humanitarian consequences, severe social and economic depression of the affected regions and associated psychological problems of the general public and the workers had become the most significant problem to be addressed by the authorities. The majority of the affected land is now safe for life and economic activities. However, in the Chernobyl Exclusion Zone and in some limited areas of Belarus, Russia and Ukraine some restrictions on land-use should be retained for decades to come. Most of the 600,000 emergency and recovery operation workers and five million residents of the contaminated areas in Belarus, Russia and Ukraine received relatively minor radiation doses which are comparable with the natural background levels. Apart from the dramatic increase in thyroid cancer incidence among those exposed at a young age and some increase of leukaemia and solid cancer in most exposed workers, there is no clearly demonstrated increase in the somatic diseases due to radiation.

Twenty years' application of agricultural countermeasures following the Chernobyl accident: lessons learned.

The accident at the Chernobyl NPP (nuclear power plant) was the most serious ever to have occurred in the history of nuclear energy. The consumption of contaminated foodstuffs in affected areas was a significant source of irradiation for the population. A wide range of different countermeasures have been used to reduce exposure of people and to mitigate the consequences of the Chernobyl accident for agriculture in affected regions in Belarus, Russia and Ukraine. This paper for the first time summarises key data on countermeasure application over twenty years for all three countries and describes key lessons learnt from this experience.

Soil-dependent uptake of 137Cs by mushrooms: experimental study in the Chernobyl accident areas.

The influence of agrochemical properties of forest soils and growth conditions on 137Cs aggregated transfer factors from soil to different species of forest mushrooms have been analysed. Statistically significant correlations between 137Cs soil to mushroom aggregated transfer factors and agrochemical soil properties have been revealed. The experimental data show that 137Cs aggregated transfer factors depend on the mushroom's trophic group, biological family, genus and species. They also strongly depend on forest soil properties and their values can be estimated with the use of multiple regression equations constructed from agrochemical soil parameters which most closely correlate with the 137Cs transfer parameters for particular mushroom groups.

External and internal irradiation of a rural Bryansk (Russia) population from 1990 to 2000, following high deposition of radioactive caesium from the Chernobyl accident.

In 1990, a joint Nordic-Russian project was initiated in order to make independent estimations of the effective dose to selected groups of inhabitants in a highly contaminated area around the city of Novozybkov in the western Bryansk region of Russia. The inhabitants were living in six villages with initial contamination levels of (137)Cs between 0.9 and 2.7 MBq m(-2). Some villages had been decontaminated, others not. Both school children and adults participated in the study. The external irradiation of 100-130 inhabitants was determined during 1 month in September-October each year from 1990 to 2000 (except 1999), using individual thermoluminescent dosemeters. The body burden of (137,134)Cs was determined by in vivo measurements in about 500 inhabitants annually from 1991 to 2000, and for a subgroup also with analysis of the (137)Cs concentration in urine. The mean effective dose (E) from external and internal irradiation due to (137,134)Cs deposition varied between 2.5 and 1.2 mSv per year between 1990 and 2000. The total mean E decreased, on average, by 9% per year, while the mean external dose decreased by 16% per year. The dose rate from internal radiation decreased more slowly than the dose rate from external radiation, and also showed an irregular time variation. The contribution from the internal dose to the total E was 30-50%, depending on the village. Predictions for the long-term changes in the effective dose to people living in the areas are presented. The cumulated E for the 70 years following the accident was estimated to be about 90 mSv with the assumption that both internal and external dose decrease by 2% per year after year 2000. The highest E during a life-time received by single individuals living in the area may amount to around 500 mSv considering the individual variations in E.

Model testing using data on 137Cs from Chernobyl fallout in the Iput River catchment area of Russia.

Data collected for 10 years following the Chernobyl accident in 1986 have provided a unique opportunity to test the reliability of computer models for contamination of terrestrial and aquatic environments. The Iput River scenario was used by the Dose Reconstruction Working Group of the BIOMASS (Biosphere Modelling and Assessment Methods) programme. The test area was one of the most highly contaminated areas in Russia following the accident, with an average contamination density of 137Cs of 800,000 Bq m-2 and localized contamination up to 1,500,000 Bq m-2, and a variety of countermeasures that were implemented in the test area had to be considered in the modelling exercise. Difficulties encountered during the exercise included averaging of data to account for uneven contamination of the test area, simulating the downward migration and changes in bioavailability of 137Cs in soil, and modelling the effectiveness of countermeasures. The accuracy of model predictions is dependent at least in part on the experience and judgment of the participant in interpretation of input information, selection of parameter values, and treatment of uncertainties.

Lake fish as the main contributor of internal dose to lakeshore residents in the Chernobyl contaminated area.

Two field expeditions in 1996 studied 137Cs intake patterns and its content in the bodies of adult residents from the village Kozhany in the Bryansk region, Russia, located on the shore of a drainless peat lake in an area subjected to significant radioactive contamination after the 1986 Chernobyl accident. The 137Cs contents in lake water and fish were two orders of magnitude greater than in local rivers and flow-through lakes, 10 years after Chernobyl radioactive contamination, and remain stable. The 137Cs content in lake fish and a mixture of forest mushrooms was between approximately 10-20 kBq/kg, which exceeded the temporary Russian permissible levels for these products by a factor of 20-40. Consumption of lake fish gave the main contribution to internal doses (40-50%) for Kozhany village inhabitants Simple countermeasures, such as Prussian blue doses for dairy cows and pre-boiling mushrooms and fish before cooking, halved the 137Cs internal dose to inhabitants, even 10 years after the radioactive fallout.