A radiation protection approach to assessing population risk for threshold-type radiobiological effects

The potential harm to a population exposed to radiation from a nuclear accident, such as the one that recently occurred at the Chernobyl plant in the Soviet Union, is of concern to many individuals. The average dose to a population is a useful index of harm (IH) only for linear, nonthreshold-type, quantal (i.e., all-or-none) effects. For such radiobiological effects, the expected harm to the population is linearly related to the average dose. However, for nonstochastic effects, it is not. An IH is proposed for threshold-type nonstochastic effects which is based on a form of the Weibull model where, at low to moderate doses, the individual risk at dose X = D/D50 is given by the approximation Risk = ln(2)XV; where D50 is the absorbed radiation dose that produces the specified effect in one-half the population, D is the absorbed radiation dose, and V is a positive parameter. The dose, X, is in units of the D50. Use of this form of the Weibull model is limited to doses such that X is small in comparison to 1. An IH for the population can be obtained by defining a new variable, P = XV, in dimensionless units, because the individual risk is linearly related to P at low and moderate doses. The average value for P (given by [P]) for an exposed population can be used as an IH for the population when the maximum value for P does not exceed 1. Both P and [P] can be regarded as theoretical doses. The average risk for the population in terms of the average dose [P] is given by ln(2)*[P], and the expected cases of nonstochastic effects among N individuals by N*ln(2)*[P]. As an example of the application of the average dose [P], the expected cases of temporary sterility in males among the approximately 135,000 people evacuated within 30 km of the Chernobyl plant is calculated to be about 200. The cases of sterility would be expected to come from those males exposed to doses to the testes of about 0.35 Gy or higher. No cases of sterility would be expected for individuals exposed to lower doses.     

Detection limit of electron spin resonance for Japanese deciduous tooth enamel and density separation method for enamel–dentine separation

Electron spin resonance (ESR) dosimetry is one of the most powerful tools for radiation dose reconstruction. The detection limit of this technique using human teeth is reported to be 56 mGy or 67 mGy; however, the absorbed dose of Fukushima residents after the Fukushima Daiichi Nuclear Power Plant (FNPP) accident was estimated to be lower than this detection limit. Our aim is to assess the absorbed radiation dose of children in Fukushima Prefecture after the accident; therefore, it is important to estimate the detection limit for their teeth. The detection limit for enamel of deciduous teeth of Japanese children separated by the mechanical method is estimated to be 115.0 mGy. The density separation method can effectively separate enamel from third molars of Japanese people. As we have collected thousands of teeth from children in Fukushima, the present technique may be useful to examine their external absorbed dose after the FNPP accident.     

The Chernobyl experience in the area of retrospective dosimetry

The Chernobyl accident, which occurred on 26 April 1986 at a nuclear power plant located less than 150 km north of Kiev, was the largest nuclear accident to date. The unprecedented scale of the accident was determined not only by the amount of released activity, but also by the number of workers and of the general public involved, and therefore exposed to increased doses of ionising radiation. Due to the unexpected and large scale of the accident, dosimetry techniques and practices were far from the optimum; personal dosimetry of cleanup workers (liquidators) was not complete, and there were no direct measurements of the exposures of members of the public. As a result, an acute need for retrospective dose assessment was dictated by radiation protection and research considerations. In response, substantial efforts have been made to reconstruct doses for the main exposed cohorts, using a broad variety of newly developed methods: analytical, biological and physical (electron paramagnetic resonance spectroscopy of teeth, thermoluminescence of quartz) and modelling. This paper reviews the extensive experience gained by the National Research Center for Radiation Medicine, Academy of Medical Sciences, Ukraine in the field of retrospective dosimetry of large cohorts of exposed population and professionals. These dose reconstruction projects were implemented, in particular, in the framework of epidemiological studies, designed to follow-up the medical consequences of the Chernobyl accident and study health effects of ionizing radiation, particularly Ukrainian-American studies of cataracts and leukaemia among liquidators.     

Individual dose reconstruction among residents living in the vicinity of the Semipalatinsk nuclear test site using EPR spectroscopy of tooth enamel

Individual accumulated doses were determined by EPR spectroscopy of tooth enamel for 26 adult persons residing in territories adjacent to the Semipalatinsk Nuclear Test Site (SNTS). The absorbed dose values due to radiation from nuclear tests were obtained after subtracting the contribution of natural background radiation from the total accumulated dose. The determined dose values ranged up to 250 mGy, except for one person from Semipalatinsk city with a measured dose of 2.8 +/- 0.4 Gy. Increased dose values were determined for the individuals whose teeth were formed before 1962, the end of the atmospheric nuclear tests. These values were found to be significantly larger than those obtained for a group of younger residents of heavily exposed territories and the residents of territories not exposed to radioactive fallout. These increased dose values are consistent with those based on officially registered data for the Northeastern part of Kazakstan adjacent to SNTS, which was exposed to high levels of radioactive fallout from nuclear tests in period 1949-1962.     

Cytogenetic biodosimetry for Fukushima travelers after the nuclear power plant accident: no evidence of enhanced yield of dicentrics

Individuals who traveled to contaminated areas after the Fukushima nuclear accident have concerns about the health effects. However, medical follow-up for any adverse health effects will be difficult without personal dose measurements. Cytogenetic biodosimetry is a reasonable method of assessing absorbed doses retrospectively. We analyzed dicentric chromosomes for 265 Fukushima travelers, mostly journalists and rescue workers, who had been dispatched to northeastern Japan during the nuclear emergency. As a control group, 37 healthy volunteers who had not visited Japan since the accident were enrolled. Yields of dicentrics and absorbed doses calculated from a dose-response calibration curve for travelers and the control group were compared. The cut-off level for dicentric chromosomes in the controls was 3.5 per 1000 cells. Of the 265 travelers, 31 had elevated numbers of dicentrics (High-Dics group) while 234 were below the cut-off (Normal-Dics group). All but one of the individuals in the High-Dics group also reported a significantly higher number of medical exposures to radiation within the past three years compared with the Normal-Dics or control groups. The 225 travelers with no history of medical exposure showed no difference of dicentrics yield compared to the control group. Our data indicate that Fukushima travel alone did not enhance the yield of dicentrics.     

单位中子注量照射中国参考人产生的全身平均吸收剂量

目的 研究不同能量E单位中子注量照射人体时产生的全身平均吸收剂量FD(E),为核事故或中子照射事故中的中子剂量评价提供基本数据。方法 根据ICRP74号出版物提供的单位中子注量对拟人模体不同器官和组织产生的吸收剂量,用中国参考人5个质量较大的主要器官和组织:红骨髓、肝、肺、胃和直肠的质量进行权重计算FD(E)。结果 获得了不同能量中子的FD(E)及²⁵²Cf/²³⁵U裂变中子谱权重的F_DCf/F_DU。结论 在事故时入射到人体上的中子谱及中子注量一旦被确定,使用FD(E)就能方便地计算出受照射者的全身中子吸收剂量。     

Improvement of accuracy of chromosome aberration analysis for biological radiation dosimetry

The frequency of chromosome aberrations in circulating lymphocytes is accepted as being the most reliable indicator of the absorbed dose of radiation. Researches done to improve the accuracy of cytogenetic analysis are described in this review. These include investigations of in vitro factors that affect the yield of radiation-induced aberrations and of in vivo factors that affect the chromosomal radiosensitivity of individuals. Improved chromosome-painting methods for accurate judgment of dicentrics and translocations are introduced. The practicality of these advanced cytogenetic techniques is shown by examinations of individuals exposed in the radiation accident at Tokaimura in 1999.     

High frequency of simple and complex chromosome aberrations detected in the Tokai-mura survivor four and five years after the 1999 criticality accident

In September 1999 a criticality accident occurred in a uranium processing plant in Tokai-mura, Japan. During the accident, three workers (A, B and C) were exposed to high acute doses of neutrons and γ-rays: workers A and B fatally and worker C to an estimated whole body absorbed dose of 0.81 Gy neutrons and 1.3 Gy γ-rays. We obtained fixed peripheral blood lymphocytes (PBL) preparations from worker C approximately four and five years after the accident and assayed by 24 colour karyotyping (M-FISH) to determine the frequency and complexity of chromosome aberrations present. We observed a high frequency of simple reciprocal translocations, which we used to provide a rough estimation of dose and, in addition, for the assessment of the emergence of any clinically-relevant clonal exchanges. We did not observe any evidence of clonality but did find some evidence suggesting chromosome 1 as being preferentially involved in exchanges in stable cells. We also detected a relatively high frequency of damaged cells containing complex chromosome aberrations, of both the stable and unstable types. Qualitatively these complex aberrations were consistent with those observed to be induced after exposure to low doses of high-LET radiation or moderate doses of low-LET radiation, supporting the suggestion that heavily damaged cells can be quite long-lived in vivo.     

Electron spin resonance dosimetric properties of bone

The characteristics of electron spin resonance (ESR) dosimetry using bovine bone samples are described. The number of paramagnetic centers created by gamma radiation in the inorganic bone matrix was measured as a function of absorbed dose. The minimum detectable dose was 0.5 Gy for 60Co gamma rays. The response was linear up to the maximum dose studied (30 Gy) and independent of dose rate up to the maximum dose rate used (1.67 Gy min-1). For different bone samples the reproducibility was 5%. This method may be valuable for nuclear accident dosimetry.     

日本福岛事故10周年剂量与健康效应评估

为简述并探讨福岛核事故10年来造成的应急人员和公众的受照剂量及其健康影响,全面梳理评估联合国原子辐射效应科学委员会的最新报告和其他重要研究成果,并追踪含氚废水排放等近期热点问题。结果显示,由于福岛事故造成的公众受照剂量较低,无法观察到白血病和甲状腺癌等发病率的增加;事故救援人员中已经有4例因患白血病、甲状腺癌被认定为工伤;福岛县及周边地区生产的大部分食品放射性铯浓度已低于100 Bq/kg的新标准限值。福岛事故中一些应急防护行动未能有效实施,导致部分公众接受了本可避免或降低的照射;同时,部分过度防护措施又造成弊大于利,并引起社会心理效应。此外,我国应持续关注和监测评估日本核污水排放的影响。     

The fate of chromosomal aberrations in 137Cs-exposed individuals in the Goiania radiation accident

Following the Goiania radiation accident, lymphocytes from 110 exposed or potentially exposed individuals were analyzed for the frequencies of chromosomal aberrations (dicentrics and centric rings) to estimate absorbed radiation dose. Dose estimates for 21 subjects exceeded 1.0 Gy, and for eight subjects they exceeded 4.0 Gy. Four of the subjects died. After the emergency period, a cytogenetic follow-up of 10 of the highest exposed patients was started. The results suggest that the average disappearance half-time of lymphocytes containing dicentric and centric rings was 130 d, which is shorter than the usually accepted value of 3 y reported in the literature.     

Guidelines for Exposure Assessment in Health Risk Studies Following a Nuclear Reactor Accident

Background: Worldwide concerns regarding health effects after the Chernobyl and Fukushima nuclear power plant accidents indicate a clear need to identify short- and long-term health impacts that might result from accidents in the future. Fundamental to addressing this problem are reliable and accurate radiation dose estimates for the affected populations. The available guidance for activities following nuclear accidents is limited with regard to strategies for dose assessment in health risk studies.Objectives: Here we propose a comprehensive systematic approach to estimating radiation doses for the evaluation of health risks resulting from a nuclear power plant accident, reflected in a set of seven guidelines.Discussion: Four major nuclear reactor accidents have occurred during the history of nuclear power production. The circumstances leading to these accidents were varied, as were the magnitude of the releases of radioactive materials, the pathways by which persons were exposed, the data collected afterward, and the lifestyle factors and dietary consumption that played an important role in the associated radiation exposure of the affected populations. Accidents involving nuclear reactors may occur in the future under a variety of conditions. The guidelines we recommend here are intended to facilitate obtaining reliable dose estimations for a range of different exposure conditions. We recognize that full implementation of the proposed approach may not always be feasible because of other priorities during the nuclear accident emergency and because of limited resources in manpower and equipment.Conclusions: The proposed approach can serve as a basis to optimize the value of radiation dose reconstruction following a nuclear reactor accident.Citation: Bouville A, Linet MS, Hatch M, Mabuchi K, Simon SL. 2014. Guidelines for exposure assessment in health risk studies following a nuclear reactor accident. Environ Health Perspect 122:1–5; http://dx.doi.org/10.1289/ehp.1307120     

Estimation of absorbed dose of beta radiation into the critical tissues by a single injection of tritiated water

The biological effects of tritium in humans need to be clarified, because the chances of humans becoming exposed to tritium beta radiation may increase with the development of the nuclear fusion reactor. To evaluate the biological effects of tritium, it is necessary to estimate exactly the absorbed dose from the tritium beta rays in the tissue. In many reports, the absorbed dose of HTO in the tissues is estimated from the tritium content in body fluid and dose calculations are customarily based upon the water content of soft tissues, which is taken to be 0.7 to 0.8. However, these methods may not show the exact absorbed dose in the organs. In the present study, the radioactivity of the critical tissues was measured directly using a sample oxidizer and the absorbed dose was calculated from the radioactivity of tritium in the tissues. Details on the method for calculation of the absorbed dose in tissues of the mouse is shown in this report. The results suggest that the absorbed dose should be obtained from the radioactivity in the tissues.     

Radiation epidemiology: a perspective on Fukushima

For nearly 100 years, epidemiologic studies of human populations exposed to ionising radiation have provided quantitative information on health risks. High dose deterministic (tissue reaction) effects result when sufficient numbers of functioning cells are killed, such as in bone marrow depression that can lead to death. Lower dose stochastic effects are probabilistic in nature and include an increased risk of cancer later in life and heritable genetic defects, although genetic conditions in the children of irradiated parents have yet to be convincingly demonstrated. Radiation studies are of diverse populations and include not only the Japanese atomic bomb survivors, but also patients treated with radiation for malignant and non-malignant disease; patients exposed for diagnostic purposes; persons with intakes of radionuclides; workers occupationally exposed; and communities exposed to environmental and accidentally released sources of radiation. Much is known about radiation and its risks. The major unanswered question in radiation epidemiology, however, is not whether radiation causes cancer, but what the level of risk is following low dose (<100 mSv) or low dose rate exposures. Paracelsus is credited with first articulating that the 'poison is in the dose', which for radiation epidemiology translates as 'the lower the dose, the lower the risk' and, an important corollary, the lower the dose, the greater the difficulty in detecting any increase in the number of cancers possibly attributable to radiation. In contrast to the Chernobyl reactor accident, the Fukushima reactor accident has to date resulted in no deterministic effects and no worker deaths. Estimates to date of population doses suggest very low uptakes of radioactive iodine which was a major determinant of the epidemic of thyroid cancer following childhood exposures around Chernobyl. The estimates to date of population doses are also much lower (and the distribution much narrower) than the doses for which cancer excesses have been detected among atomic bomb survivors after 60 years of follow-up. Studies of populations exposed to low doses are also limited in their ability to account for important lifestyle factors, such as cigarette smoking and medical x-ray exposures, which could distort findings. Studies of the Fukushima population should be and are being considered for reassurance and health care reasons. Apart from as regards the extreme psychological stress caused by the horrific loss of life following the tsunami and the large-scale evacuation from homes and villages, such studies have limited to no chance of providing information on possible health risks following low dose exposures received gradually over time--the estimated doses (to date) are just too small.     

Extended conversion coefficients for use in radiation protection of the embryo and fetus against external neutrons from 10 MeV to 100 GeV

External neutron exposure is of concern in the environment and in some workplaces. Dose assessments for neutrons frequently rely on fluence-to-absorbed dose conversion coefficients. A problem of concern in radiation protection is exposure of pregnant women to ionizing radiation because of the high radiosensitivity of the embryo and fetus. While neutron fluence-to-dose conversion coefficients for adults are recommended in ICRP publications and ICRU reports, conversion coefficients for embryos and fetuses are not given in the publications. This study uses the Monte Carlo code MCNPX to determine mean absorbed doses to the embryo and fetus when the mother is exposed to neutron fields. A previous study has dealt with neutrons from 1 eV to 10 MeV. In this study, monoenergetic neutrons ranging from 10 MeV to 100 GeV are considered. The irradiation geometries include antero-posterior, postero-anterior, lateral, rotational, and isotropic. At each of these standard irradiation geometries, absorbed doses to the fetal brain and body are calculated for the embryo of 8 wk and the fetus of 3, 6, or 9 mo. Neutron fluence-to-absorbed dose conversion coefficients are derived for the four prenatal ages. The results showed that the fetus at about 3 mo of prenatal age should receive more radiation protection to prevent long-term brain damage. During prenatal life, the fetus generally receives the highest absorbed dose per unit neutron fluence for antero-posterior irradiation. In cases where the irradiation geometry is not specified or not adequately known, conversion coefficients of AP-irradiation can therefore be used in a conservative dose assessment of fetus exposure to external neutrons.     

Absorption of strontium from the gastrointestinal tract into plasma in healthy human adults

The radioactive isotopes of strontium have always been a major concern in radiation protection. Currently, radiostrontium is of interest for evaluation of the health effects of the Chernobyl accident and for epidemiological studies in populations exposed to releases from the Mayak nuclear facilities in Russia. Ingestion is one of the most important exposure pathways involving radioactive strontium. The main sources of published data on the fraction of the ingested strontium that is transferred to plasma (f1) are summarized. For some of these studies, the original data had to be reanalyzed and a new iterative method to account for the elimination in feces of strontium of endogenous origin (i.e., that was absorbed to blood and has already been returned into feces) was employed. Data indicate no significant dependence of the absorbed fraction on sex or age at exposure within the adult group, but absorption of strontium is reduced if the intake of stable calcium is very high and is enhanced if the intake of calcium is very low. The probability distribution function of f1 values is well represented by a lognormal curve with a geometric mean of 22.3% and a geometric standard deviation of 1.44 (95% confidence interval 10.9% to 45.6%, or about a factor of 2 around the geometric mean). This distribution can be considered representative for the variability of the f1 values in a population of healthy adults.     

“散布式”应急监测系统的研发

目的 在核与辐射事故情况下快速获取现场辐射场信息并加强属地化应急响应支持。方法 采用GM计数管和NaI (Tl)闪烁体相结合的方式,拓展探测单元的γ剂量率测量量程并实时获取现场核素信息,监测数据通过内置冗余的无线传输方式(3G和RF)传至数据处理系统,系统具备气象和地理信息接口,能够实现现场污染趋势的可视化,并可对核事故释放的烟羽源项进行"反演"计算。结果 探测单元结构轻便、可靠,能灵活地"散布"在事故现场周围,及时地为应急指挥中心提供决策支持。结论 测试表明,本系统能够在核与辐射事故情况下为应急决策提供"一站式"服务。     

Thyroid cancer incidence among people living in areas contaminated by radiation from the Chernobyl accident

As a result of the Chernobyl nuclear power plant accident, massive amounts of radioactive materials were released into the environment and large numbers of individuals living in Belarus, Russia, and Ukraine were exposed to radioactive iodines, primarily 131I. Iodine-131 concentrated in the thyroid gland of residents of the contaminated areas, with children and adolescents being particularly affected. In the decade after the accident, a substantial increase in thyroid cancer incidence was observed among exposed children in the three affected countries, and compelling evidence of an association between pediatric thyroid cancer incidence and radiation exposure to the thyroid gland accumulated. The data currently available suggest that both the magnitude and patterns of thyroid cancer risk are generally consistent with those reported following external exposure. Based on data from case-control studies, iodine deficiency appeared to enhance the risk of developing thyroid cancer following exposure from Chernobyl. Results from a recent large cohort study, however, did not support these findings. Data on adult exposure are limited and not entirely consistent. Similarly, information on thyroid cancer risks associated with in utero exposure is insufficient to draw conclusions. The lack of information on these two population groups indicates an important gap that needs to be filled. Twenty years after the accident, excess thyroid cancers are still occurring among persons exposed as children or adolescents, and, if external radiation can be used as a guide, we can expect an excess of radiation-associated thyroid cancers for several more decades. Since considerable uncertainties about the long-term health effects from Chernobyl remain, continued follow-up of the exposed populations should provide valuable information.     

Current status and epidemiological research needs for achieving a better understanding of the consequences of the Chernobyl accident

Twenty years after the Chernobyl accident, there is no clearly demonstrated increase in the incidence of cancers in the most affected populations that can be attributed to radiation from the accident, except for the dramatic increase in thyroid cancer incidence among those exposed in childhood and adolescence. Increases in the incidence of cancers and other diseases have been reported in Belarus, the Russian Federation, and Ukraine, but much of the increase appears to be due to other factors, including improvements in diagnosis, reporting, and registration. Recent findings indicate a possible doubling of leukemia risk among Chernobyl liquidators and a small increase in the incidence of premenopausal breast cancer in the very most contaminated districts. Increased risks of cardiovascular diseases and cataracts have also been reported. These findings, however, need confirmation in well-designed analytical epidemiological studies with careful individual dose reconstruction. The absence of demonstrated increases in cancer risk--apart from thyroid cancer--is not the proof that no increase has in fact occurred. Based on the experience of atomic bomb survivors, and assuming that there is a linear, no-threshold dose-response relationship between exposure to ionizing radiation and the development of cancer in humans, a small increase in the relative risk of cancer is expected, even at the low to moderate doses received. Given the large number of individuals exposed, the absolute number of cancer cases caused could be substantial, particularly in the future. It is therefore essential to continue to use population registries to monitor trends in disease morbidity and mortality in the most contaminated areas, as well as among liquidators, in order to assess the public health impact of the accident. Studies of selected populations and diseases are also essential in order to study the real effect of the accident and compare it to predictions. Careful studies may in particular provide important information on the effect of exposure rate and exposure type in the low to medium dose range and on factors that may modify radiation effects. As such, they may have important consequences for the radiation protection of patients and of the general population in case of further nuclear emergencies.     

上海市PET/CT工作场所放射性水平监测与分析

目的 了解上海市PET/CT使用基本状况,通过对PET/CT工作场所放射性水平的监测,掌握目前上海市PET/CT场所防护情况。方法 普查上海市PET/CT医疗机构,通过γ辐射空气吸收剂量率和β表面污染两项检测指标进行现场监测。结果 截止2011年底,上海市共有PET/CT 13台。现场检测表明,候诊室及注射室γ辐射空气吸收剂量率水平相对较高,候诊室门四周最高达19 552 nSv/h,注射室桌面最高达6 136 nSv/h,注射室中央最高达5408 nSv/h。PET/CT工作场所β表面污染无超国家标准限值情况,但注射室内,尤其是传递窗及废物桶四周仍然较高。结论 上海市PET/CT工作场所放射防护较得当,工作场所表面污染水平能控制在标准限值内,但国家标准对PET/CT等核医学场所的γ辐射空气吸收剂量率并没有限值,防护重点仍是外照射的防护。