The Fukushima Health Management Survey: estimation of external doses to residents in Fukushima Prefecture

Spectroscopic and dosimetric comparison of tooth enamel separation methods for EPR retrospective dosimetry

Precise estimation of individual radiation dose utilizing biomaterials (fingernail, bone, and tooth) is very challenging due to their complex sample processing. Despite, tooth enamel, the most mineralized tissue of tooth is used for this purpose due to its high radiation sensitivity and ability to produce radiation induced long lived CO2- radicals. However, human teeth are not always available, and invasive nature of sample collection adds to the complexity making dose estimation difficult. In such cases, animal teeth (goat, cow, and moose) can be used as a substitute for human teeth due to comparable enamel sensitivity. Moreover, separation of enamel from dentine is a crucial step towards accurate dose estimation from irradiated teeth. In this work, Indian goat teeth were used as it was readily available to us and the comparison of goat enamel sensitivity to radiation was found to be within ∼7.4 % that of human. The enamel samples were separated following two chemical methods; (1) density separation using sodium polytungstate, (2) alkaline denaturation using NaOH and the quality was compared based on their purity and radiation sensitivity. Combined results of spectroscopic characterization using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman analysis authenticated the crystallinity and purity of the separated enamel samples. The radiation sensitivity of separated enamel samples was compared by electron paramagnetic resonance (EPR) analysis as a part of dosimetric characterization. The suitability of both the samples for retrospective dosimetry and epidemiological studies was checked by validating the dose estimated from separated enamel samples with standard alanine/EPR dosimeter.

Confounding factors and biases involved in regional differences in the detection rate of thyroid cancer in the second-round Thyroid Ultrasound Examination: the Fukushima Health Management Survey

In response to concerns about health due to radiation exposure, the Fukushima Prefecture launched the Thyroid Ultrasound Examination program for residents aged 0-18 years at the time of the earthquake. Herein, we considered the confounding factors involved in the regional differences in the development of thyroid cancer. In this study, the 242 065 individuals who participated in both first- and second-round surveys were classified into four groups by address according to their air radiation dose. The number of participants diagnosed as malignant or suspicious for malignancy by cytological examination were 17, 38, 10 and 4 with detection rates of 53.8, 27.8, 21.7 and 14.5 per 100 000 participants in Regions 1, 2, 3 and 4, respectively. Sex (P = 0.0400), age at the time of the primary examination (P < 0.0001) and interval between the first- and second-round surveys (P < 0.0001) were significantly different among the four regions, and these were suspected to be confounding factors affecting regional differences in malignant nodule detection rates. In addition, significant regional differences were observed in the participation rate in the confirmatory examination (P = 0.0037) and the fine needle aspiration cytology implementation rate (P = 0.0037), which could be potential biases. No significant regional differences in the detection of malignant nodules were found in the multivariate logistic regression analysis after adjusting for the survey interval alone or for sex, age and survey interval. The confounding factors and biases identified in this study that may have important impacts on thyroid cancer detection rate should be fully considered in future studies.

"I'd like to let people know what we did:" values of Fukushima medical students following the Great East Japan Earthquake

BACKGROUND

The Great East Japan Earthquake and the resulting tsunami and nuclear disaster on March 11, 2011 have had a profound and lasting effect on residents of Japan's Fukushima Prefecture, particularly among evacuees. While there continues to be extensive news coverage and academic study of Fukushima Prefecture's recovery, there has been little exploration of individual narratives. This study aims to illuminate some individual stories of medical students at Fukushima Medical University (FMU) who lived in the Prefecture at the time of the Earthquake.

METHODS

A qualitative approach was taken in order to investigate individuals' experiences with the goal of adding a personal dimension to quantitative studies on the subject. 10 open-ended ethnographic interviews were conducted with medical students at FMU in years 1-5 who lived in Fukushima Prefecture at the time of the Great East Japan Earthquake. All interviews were audio recorded and transcribed. Transcriptions were reviewed using inductive thematic analysis under the lens of ethnographic anthropology.

RESULTS

Three major themes emerged from these interviews: first, that the events following the Earthquake influenced not only these students' decisions to pursue careers in medicine, but the ways in which they hope to practice medicine in the future. Second, that these students were motivated to share their experiences by a want to change Fukushima Prefecture's public image. And lastly, that the students viewed the opportunity to discuss their experiences through these interviews as healing, both for themselves and for the future.

CONCLUSIONS

While multiple factors undoubtably contributed these students' medical education, they cite the Earthquake as essential to their approach to their medical careers. Additionally, opportunities for the participants to discuss their experiences following the Earthquake appear to be rare but valued, as the students view their stories as their "legacies." The enduring, burdening effects of the Earthquake appear to have galvanized the participating students to act on behalf of their communities and their Prefecture. Further qualitative studies in more generalizable populations are needed to improve and deepen our understanding of the societal, cultural, and personal impacts of the Great East Japan Earthquake.

Comparison between external and internal doses to the thyroid after the Fukushima Daiichi Nuclear Power Plant accident

To analyze the association between radiation dose and thyroid cancer after the 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, external doses have often been used because of the difficulty to estimate internal thyroid doses individually due to the lack of human data. However, no evaluation has been made as to whether external dose is a good surrogate marker for internal thyroid dose individually. This study aimed at analyzing the relationship between external doses and internal thyroid doses estimated by recently developed methodology. For four municipalities affected by the accident, 200 individuals aged under 20 at the time of the accident per municipality were randomly selected, and their external and internal thyroid doses and their ratios were estimated individually. In a separate analysis, median and arithmetic mean values for external thyroid doses estimated for persons of 16 municipalities that included the above four were compared with those for previously estimated internal thyroid doses. The ratios of the median of internal thyroid dose to that of external thyroid dose in these 16 municipalities ranged from 0.56 to 13.8 for 15-year-old children and 0.91 to 21.1 for 1-year-old children. No consistent relationship between external and internal thyroid doses was found in all 16 municipalities. Thus, thyroid doses from both external and internal exposures should be used to analyze the association between radiation dose and thyroid cancer detection rates for persons who lived in Fukushima Prefecture at the time of the FDNPP accident. (240).

Associations Between External Radiation Doses and the Risk of Psychological Distress or Post-traumatic Stress After the Fukushima Daiichi Nuclear Power Plant Accident: the Fukushima Health Management Survey

BACKGROUND

The relationship between radiation levels and mental health status after a nuclear disaster is unknown. We examined the association between individual external radiation doses and psychological distress or post-traumatic stress after the Fukushima Daiichi nuclear power plant accident in March 2011 in Japan.

METHODS

The Mental Health and Lifestyle Survey was conducted from January 2012. Based on the estimated external radiation doses for the first 4 months, a total of 64,184 subjects were classified into <1 mSv, 1 to <2 mSv, and ≥2 mSv groups. Odds ratios (ORs) and 95% confidence intervals (CIs) of psychological distress and post-traumatic stress, with the <1 mSv group as the reference, were calculated using logistic regression analysis adjusted for age, sex, evacuation, perception of radiation risk, and subjective health status.

RESULTS

The prevalence of psychological distress/post-traumatic stress in the <1 mSv, 1 to <2 mSv, and ≥2 mSv groups was 15.1%/22.1%, 14.0%/20.1%, and 15.0%/21.7%, respectively. In women, although the ≥2 mSv group tended to have a higher risk of psychological distress with the age-adjusted OR of 1.13 (95% CI, 0.99-1.30), the adjusted OR decreased to 1.00 (95% CI, 0.86-1.16) after controlling for all variables. On the other hand, there were no dose-dependent associations between radiation dose and post-traumatic stress.

CONCLUSION

Although external radiation doses were not associated with psychological distress, evacuation and perception of radiation risk may increase the risk of psychological distress in women in the higher dose group.

External Doses Available for Epidemiological Studies Related to the Fukushima Health Management Survey: First 4-month Individual Doses and Municipality-average Doses for the First Year

BACKGROUND

One of the components of the Fukushima Health Management Survey (FHMS) is the Basic Survey, which estimates individual external doses for the first 4 months after the 2011 nuclear power plant accident. However, external exposure continues long-term. According to estimations by international organizations, the external dose during the first year accounts for a significant part of the long-term dose. Thus, the present study was intended to estimate the first-year doses by extrapolating the Basic Survey results.

METHODS

For most municipalities of non-evacuated areas, ambient dose rate had been continuously measured for at least one designated point in each municipality after the accident. In the present study, a municipality-average dose received by residents for a period was assumed to be proportional to the ambient dose measured at the designated point of that municipality during the same period. Based on this assumption, 4-month municipality-average doses calculated from the Basic Survey results were extrapolated to obtain first-year doses.

RESULTS

The extrapolated first-year doses for 49 municipalities in the non-evacuated areas had a good correlation with those estimated by UNSCEAR, although the extrapolated doses were generally higher (slope of the regression line: 1.23). The extrapolated municipality-average doses were in reasonable agreement (within 30%) with personal dosimeter measurements, suggesting that the extrapolation was reasonable.

CONCLUSION

The present paper reports the first 4-month average doses for all 59 municipalities of Fukushima Prefecture and the extrapolated first-year doses for 49 municipalities. The extrapolated doses will be the basis for future epidemiological studies related to the FHMS.

Achievements and Current Status of the Fukushima Health Management Survey

The Fukushima Health Management Survey (FHMS) was established in response to the Fukushima Daiichi Nuclear Power Plant accident on March 11, 2011. The primary objectives of the study are to monitor residents' long-term health and promote their future well-being, and to determine the health effects of long-term low-dose radiation exposure. This special issue summarizes the results and current status of the FHMS and discusses the challenges and future directions of the FHMS. The FHMS, a cohort study of all people who were residents in Fukushima Prefecture at the time of the accident, consists of a Basic Survey, Thyroid Ultrasound Examination, Comprehensive Health Check, Mental Health and Lifestyle Survey, and Pregnancy and Birth Survey. The radiation exposure was estimated based on the behavioral records examined using the Basic Survey. Although the response rate was low in the Basic Survey, the representativeness of the radiation exposure data was confirmed using additional surveys. There appears to be no relationship between the radiation exposure and risk of thyroid cancer, although more thyroid cancer cases were detected than initially expected. The ongoing Comprehensive Health Check and Mental Health and Lifestyle Survey have provided evidence of worsening physical and mental health status. The Pregnancy and Birth Survey showed rates of preterm delivery, low birth weight, and congenital abnormalities similar to the national average. Considering the above evidence, the Fukushima Prefectural Government decided to end the Pregnancy and Birth Survey at the end of March 2021, as recommended by the Prefectural Oversight Committee. The framework of the FHMS has not changed, but the FHMS needs to adapt according to the survey results and the changing needs of the eligible residents and municipalities.

Effects of External Radiation Exposure Resulting From the Fukushima Daiichi Nuclear Power Plant Accident on the Health of Residents in the Evacuation Zones: the Fukushima Health Management Survey

BACKGROUND

Associations have been reported between lifestyle-related diseases and evacuation after the Great East Japan Earthquake (GEJE). However, the relationship between lifestyle-related diseases and the effective radiation dose due to external exposure (EDEE) after the GEJE remains unclear.

METHODS

From among 72,869 residents of Fukushima Prefecture (31,982 men; 40,887 women) who underwent a comprehensive health check in fiscal year (FY) 2011, the data of 54,087 residents (22,599 men; 31,488 women) aged 16 to 84 years were analyzed. The EDEE data of 25,685 residents with incomplete results from the basic survey, performed to estimate the external radiation exposure dose, were supplemented using multiple imputation. The data were classified into three groups based on EDEE (0 to <1, 1 to <2, and ≥2 mSv groups and associations between the incidence of diseases and EDEE from FY2011 to FY2017 were examined using a Cox proportional hazards model, with FY2011 as the baseline.

RESULTS

A higher EDEE was associated with a greater incidence of hypertension, diabetes mellitus, dyslipidemia, hyperuricemia, liver dysfunction, and polycythemia from FY2011 to FY2017 in the age- and sex-adjusted model. However, after further adjustment for evacuation status and lifestyle-related factors, the significant associations disappeared. No association was found between EDEE and other lifestyle-related diseases.

CONCLUSION

EDEE was not directly associated with the incidence of lifestyle-related diseases after the GEJE. However, residents with higher external radiation doses in Fukushima Prefecture might suffer from lifestyle-related diseases related to evacuation and the resultant lifestyle changes.

Effects of External Radiation Exposure on Perinatal Outcomes in Pregnant Women After the Fukushima Daiichi Nuclear Power Plant Accident: the Fukushima Health Management Survey

BACKGROUND

This study aimed to investigate the effects of maternal exposure to external radiation on perinatal outcomes among women who experienced the Fukushima Daiichi Nuclear Disaster (FDND) using the Fukushima Health Management Survey (FHMS).

METHODS

Data from the Pregnancy and Birth Survey and Basic Survey in the FHMS were combined to analyze external maternal radiation exposure following the FDND, and the relationship between radiation dose and perinatal outcomes was analyzed using binomial logistic regression analysis. Missing dose data were supplemented using multiple imputation.

RESULTS

A total of 6,875 individuals responded to the survey. Congenital anomalies occurred in 2.9% of patients, low birth weight (LBW) in 7.6%, small for gestation age (SGA; <10th percentile) in 8.9%, and preterm birth in 4.1%. The median maternal external radiation dose was 0.5 mSv (maximum, 5.2 mSv). Doses were classified as follows: <1 mSv (reference), 1 to <2 mSv, and ≥2 mSv. For congenital anomalies, the crude odds ratio for 1 to <2 mSv was 0.81 (95% confidence interval [CI], 0.56-1.17) (no participants with congenital anomaly were exposed to ≥2 mSv). At 1 to <2 mSv and ≥2 mSv, the respective adjusted odds ratios were 0.91 (95% CI, 0.71-1.18) and 1.21 (95% CI, 0.53-2.79) for LBW, 1.14 (95% CI, 0.92-1.42) and 0.84 (95% CI, 0.30-2.37) for SGA, and 0.91 (95% CI, 0.65-1.29) and 1.05 (95% CI, 0.22-4.87) for preterm birth.

CONCLUSION

External radiation dose due to the FDND was not associated with congenital anomalies, LBW, SGA, or preterm birth.

The Effects of the Great East Japan Earthquake on Perinatal Outcomes: Results of the Pregnancy and Birth Survey in the Fukushima Health Management Survey

There are limited studies on the long-term effects of natural/environmental disasters, especially nuclear disasters, on obstetric outcomes. This study aimed to review the results of perinatal outcomes immediately after the Great East Japan Earthquake (GEJE) and the Fukushima Daiichi Nuclear Power Plant accident, as well as their long-term trends over 8 years, in the Fukushima Health Management Survey. The annual population-based Pregnancy and Birth Survey is conducted as part of the Fukushima Health Management Survey. The Fukushima Prefecture government launched it to assess the health conditions of pregnant women and their neonates after the GEJE. The self-reported questionnaire was sent to 115,976 pregnant women by mail from January 2012, with 58,344 women responding to the questionnaire (50.3% response rate). Pregnancy complications, such as gestational hypertension, respiratory diseases, and mental disorders, increased in some women who were pregnant at the time of the earthquake and immediately after the earthquake. However, the direct effects on newborns, such as preterm birth, low birth weight, and congenital anomalies, were not immediately clear after the earthquake. Although there were significant differences in the occurrence of preterm birth and low birth weight among the districts, there was no change in the occurrences of preterm birth, low birth weight, or anomalies in newborns in Fukushima Prefecture from the fiscal year 2011 to the fiscal year 2018. Therefore, the long-term effects of the post-disaster radiation accident on perinatal outcomes are considered to be very small.

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.

Public health response and medical management of internal contamination in past radiological or nuclear incidents: A narrative review

Following a radiological or nuclear emergency, workers, responders and the public may be internally contaminated with radionuclides. Screening, monitoring and assessing any internal contamination and providing necessary medical treatment, especially when a large number of individuals are involved, is challenging. Experience gained and lessons learned from the management of previous incidents would help to identify gaps in knowledge and capabilities on preparedness for and response to radiation emergencies. In this paper, eight large-scale and five workplace radiological and nuclear incidents are reviewed cross 14 technical areas, under the broader topics of emergency preparedness, emergency response and recovery processes. The review findings suggest that 1) new strategies, algorithms and technologies are explored for rapid screening of large populations; 2) exposure assessment and dose estimation in emergency response and dose reconstruction in recovery process are supported by complementary sources of information, including 'citizen science'; 3) surge capacity for monitoring and dose assessment is coordinated through national and international laboratory networks; 4) evidence-based guidelines for medical management and follow-up of internal contamination are urgently needed; 5) mechanisms for international and regional access to medical countermeasures are investigated and implemented; 6) long-term health and medical follow up programs are designed and justified; and 7) capabilities and capacity developed for emergency response are sustained through adequate resource allocation, routine non-emergency use of technical skills in regular exercises, training, and continuous improvement.

Effects of Ionizing Radiation on Flora Ten Years after the Fukushima Dai-ichi Disaster

The aim of this work is to analyze the effects of ionizing radiation and radionuclides (like 137Cs) in several higher plants located around the Fukushima Dai-ichi Nuclear Power Plant (FNPP), evaluating both their adaptive processes and evolution. After the FNPP accident in March 2011 much attention was focused to the biological consequences of ionizing radiation and radionuclides released in the area surrounding the nuclear plant. This unexpected mishap led to the emission of radionuclides in aerosol and gaseous forms from the power plant, which contaminated a large area, including wild forest, cities, farmlands, mountains, and the sea, causing serious problems. Large quantities of 131I, 137Cs, and 134Cs were detected in the fallout. People were evacuated but the flora continued to be affected by the radiation exposure and by the radioactive dusts' fallout. The response of biota to FNPP irradiation was a complex interaction among radiation dose, dose rate, temporal and spatial variation, varying radiation sensitivities of the different plants' species, and indirect effects from other events. The repeated ionizing radiations, acute or chronic, guarantee an adaptation of the plant species, demonstrating a radio-resistance. Consequently, ionizing radiation affects the genetic structure, especially during chronic irradiation, reducing genetic variability. This reduction is associated with the different susceptibility of plant species to chronic stress. This would confirm the adaptive theory associated with this phenomenon. The effects that ionizing radiation has on different life forms are examined in this review using the FNPP disaster as a case study focusing the attention ten years after the accident.

Estimation of the Early Cs-137 Intake of Evacuees from Areas Affected by the 2011 Fukushima Daiichi Nuclear Power Plant Accident Based on Personal Behavioral Data and the Latest Atmospheric Transport and Dispersion Model Simulation

ABSTRACT

More than 9 y have passed since the 2011 nuclear disaster in Fukushima Prefecture, Japan. During this period, much effort has been spent on the dose reconstruction for Fukushima residents; however, the estimation of the internal dose due to the potential intake of the short-lived radionuclides (mainly iodine-131) has been challenging because of the lack of direct human measurements at the early phase of the accident. Our previous study revealed that the residual cesium body contents observed in delayed whole-body counter (WBC) measurements of residents from Namie-town, one of the most affected municipalities, varied greatly with the timepoint of their evacuations on 12 March 2011 when the first explosive event occurred at the accident site; i.e., the late evacuees had much higher residual cesium body contents compared to the prompt evacuees. The present study thus aimed to clarify this finding by reproducing the exposure situation based on the evacuees' personal behavioral data in combination with the latest atmospheric transport and dispersion model (ATDM) simulation for 356 selected subjects in adult and 15-y (13-17 y) age groups. The results demonstrated that the ATDM simulation-based method could reasonably reproduce the subjects' exposure situation, supporting the previous finding. However, the residual cesium-137 body contents calculated by this method were only 10%-20% of those in the subjects' WBC measurements. This large discrepancy was considered to be caused by both the present method's underestimation and the overestimation of the subjects' early intake in the WBC measurements due to a conservative intake scenario not assuming potential additional intake. Additional studies are needed to further clarify the reasons for the discrepancy and to evaluate the magnitude of the inhalation dose in the accident.

Induction of somatic mutations by low concentrations of tritiated water (HTO): evidence for the possible existence of a dose-rate threshold

Tritium is a low energy beta emitter and is discharged into the aquatic environment primarily in the form of tritiated water (HTO) from nuclear power plants or from nuclear fuel reprocessing plants. Although the biological effects of HTO exposures at significant doses or dose rates have been extensively studied, there are few reports concerning the biological effects of HTO exposures at very low dose rates. In the present study using a hyper-sensitive assay system, we investigated the dose rate effect of HTO on the induction of mutations. Confluent cell populations were exposed to HTO for a total dose of 0.2 Gy at dose rates between 4.9 mGy/day and 192 mGy/day by incubating cells in medium containing HTO. HTO-induced mutant frequencies and mutation spectra were then investigated. A significant inflection point for both the mutant frequency and mutation spectra was found between 11 mGy/day and 21.6 mGy/day. Mutation spectra analysis revealed that a mechanistic change in the nature of the mutation events occurred around 11 mGy/day. The present observations and published experimental results from oral administrations of HTO to mice suggest that a threshold dose-rate for HTO exposures might exist between 11 mGy/day and 21.6 mGy/day where the nature of the mutation events induced by HTO becomes similar to those seen in spontaneous events.

Health management and care following the Fukushima nuclear power plant accident: overview of Fukushima Health Management Survey

Following the accident at Fukushima Daiichi nuclear power plant, Fukushima Prefecture is conducting the Fukushima Health Management Survey, which has been contracted out to Fukushima Medical University. The purpose of this survey is to investigate the exposure doses and health conditions of the residents of Fukushima Prefecture in order to prevent, diagnose, and treat diseases at an early stage, and to maintain and improve the health of residents in the future.This survey consists of a basic survey to estimate external exposure doses and detailed surveys to investigate health conditions. The detailed surveys comprise: (i) thyroid ultrasound examination; (ii) comprehensive health check; (iii) mental health and lifestyle survey; and (iv) pregnancy and birth survey.In the basic survey, the external exposure dose was estimated for >466,000 people during the first 4 months after the accident; it was estimated to be <5 mSv for 99.8% of residents.The thyroid ultrasound examination included four rounds of echo examinations covering approximately 380,000 children aged <18 years at the time of the accident in each round. The first, second, third, and fourth examinations identified 116, 71, 31, and 21 children with thyroid cancer/suspected cancer, respectively. The Fukushima Prefectural Oversight Committee analysed the results from the first and second examinations, and evaluated that 'the detected increased rate is unlikely to be the impact of radiation'. However, the Oversight Committee is deliberating the future direction of thyroid examination, taking into consideration the advantages and disadvantages of the examination as well as ethical viewpoints.In the comprehensive health check, approximately 210,000 people in the evacuation area were examined, and increased rates of lifestyle-related diseases [e.g. obesity, hypertension, diabetes, and dyslipidaemia (low high-density-lipoprotein cholesterol)] were confirmed. In the mental health and lifestyle survey, approximately 210,000 people, including residents in the evacuation area, were examined. A deterioration in general mental health was found for the period immediately after the accident across a wide range of age groups, and although recovery was seen over the years, the rate of mental health issues remains above the national average. The pregnancy and birth survey revealed that the pre-term birth rate, low-birthweight rate, and rate of congenital anomalies did not differ from the national average.The purpose of Fukushima Health Management Survey is not only to collect data on the health of the residents of Fukushima Prefecture, but to provide direct support to residents regarding the health issues clarified by the survey. Moreover, various initiatives are being implemented in cooperation with various local government authorities with the aim of maintaining and promoting the health of the residents.

Communicating with residents about 10 years of scientific progress in understanding thyroid cancer risk in children after the Fukushima Dai-ichi Nuclear Power Station accident

After the Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident in 2011, radiation-related risk of childhood thyroid cancer remains a matter of concern among residents living in areas affected by radioactive plumes. As a countermeasure to that, the Fukushima Prefectural Government-in conjunction with Fukushima Medical University-began the Fukushima Thyroid Examination (FTE) campaign in 2011. As 116 definite or suspected thyroid cancer cases were found after the first round of FTE and the total number of cases was >240 as of June 2020, residents' concerns have deepened. Some researchers claim that these cases are radiation-induced, while others claim a screening effect (because FTE uses high-resolution ultrasound equipment) and express concern about over-diagnosis. Researchers therefore must address two conflicting issues: one is to elucidate radiation effects on thyroid cancer, which requires continuation of FTE; the other is to solve ethical problems associated with FTE. As to over-diagnosis, surgeons claim that early diagnosis benefits children by reducing the side-effects of treatment and prolonging disease-free survival, while cancer epidemiologists claim that early diagnosis will result in overtreatment without reducing the death rate. 'To receive FTE or not' and 'to stop FTE or not' are ongoing dilemmas for children (and their parents) and other stakeholders, respectively. To facilitate building a consensus among stakeholders, I overview recent findings about dose reconstruction, the dose-response relationship of thyroid cancer, over-diagnosis, and the natural history of thyroid cancer, all of which contribute to judging the risk-benefit balance of thyroid screening.

Lessons learned from conducting disease monitoring in low-dose exposure conditions as a counter-measure after a nuclear disaster

The complex disaster of the Great East Japan Earthquake and the Fukushima nuclear accident caused concern about their various health impacts. Many types of intervention are desired as a countermeasure, depending on the phase of the disaster cycle. The importance of developing and applying codes of conduct has recently been emphasized for post-disaster investigations. Thyroid examination as a type of cancer screening survey was launched from October 2011 after the Fukushima nuclear accident as part of the Fukushima Health Management Survey. In this article, we reviewed the results of three rounds of thyroid examination from 2011 to 2018, and summarized the points to consider in the health survey conducted after the Fukushima nuclear accident. Large-scale mass screening by ultrasound thyroid examination resulted in many cancer diagnoses, >200 cases from a large reservoir of thyroid cancer that goes mainly unnoticed without screening. To prevent the harms of such over-diagnosis, we should be aware of the disadvantage of mass-screening based on the expected natural history of thyroid cancer. A change in strategy from mass-screening to individual monitoring is urgently needed according to international recommendations that are opposed to thyroid ultrasound cancer screening even after a nuclear disaster. To guarantee autonomy and informed choice on post-disaster disease monitoring for residents in a disaster-zone, it is important to set protocol participation and on a voluntary code of conduct basis.

The mental health status of children who have been evacuated or migrated from rural areas in Fukushima prefecture after the Fukushima daiichi nuclear power station accident:results from the Fukushima health management survey

INTRODUCTION

We evaluated the mental health status of children residing in Kawauchi village (Kawauchi), Fukushima Prefecture, after the 2011 accident at the Fukushima Daiichi Nuclear Power Station, based on the children's experience of the nuclear disaster.

METHODS

We conducted this cross-sectional study within the framework of the Fukushima Health Management Survey (FHMS);FHMS data on age, sex, exercise habits, sleeping times, experience of the nuclear disaster, and the "Strengths and Difficulties Questionnaire (SDQ)" scores for 156 children from Kawauchi in 2012 were collected. Groups with and without experience of the nuclear disaster - "nuclear disaster (+)" and "nuclear disaster (-)" - were also compared.

RESULTS

Our effective response was 93 (59.6%);the mean SDQ score was 11.4±6.8 among elementary school-aged participants and 12.4±6.8 among junior high school-aged ones. We statistically compared the Total Difficulties Scores (TDS) and sub-item scores of the SDQ between "elementary school" and "junior high school" or "nuclear disaster" (+) and (-). There was no significant difference between these items.

CONCLUSIONS

We found indications of poor mental health among elementary and junior high school-aged children in the disaster area immediately following the accident, but no differences based on their experience of the nuclear disaster. These results indicate the possibility of triggering stress, separate to that from experiences related to the nuclear disaster, in children who lived in affected rural areas and were evacuated just after the nuclear disaster.

Discriminative Measurement of Absorbed Dose Rates in Air from Natural and Artificial Radionuclides in Namie Town, Fukushima Prefecture

Ten years have elapsed since the accident at the Fukushima Daiichi Nuclear Power Plant in 2011, and the relative contribution of natural radiation is increasing in Fukushima Prefecture due to the reduced dose of artificial radiation. In order to accurately determine the effective dose of exposure to artificial radiation, it is necessary to evaluate the effective dose of natural as well as artificial components. In this study, we measured the gamma-ray pulse-height distribution over the accessible area of Namie Town, Fukushima Prefecture, and evaluated the annual effective dose of external exposure by distinguishing between natural and artificial radionuclides. The estimated median (range) of absorbed dose rates in air from artificial radionuclides as of 1 April 2020, is 133 (67–511) nGy h⁻¹ in the evacuation order cancellation zone, and 1306 (892–2081) nGy h⁻¹ in the difficult-to-return zone. The median annual effective doses of external exposures from natural and artificial radionuclides were found to be 0.19 and 0.40 mSv in the evacuation order cancellation zone, and 0.25 and 3.9 mSv in the difficult-to-return zone. The latest annual effective dose of external exposure discriminated into natural and artificial radionuclides is expected to be utilized for radiation risk communication.

External Radiation Dose, Obesity, and Risk of Childhood Thyroid Cancer After the Fukushima Daiichi Nuclear Power Plant Accident: The Fukushima Health Management Survey

BACKGROUND

The 2011 Great East Japan Earthquake led to a nuclear accident at Fukushima Daiichi Nuclear Power Plant. This study examines the associations of radiation dose and lifestyle factors with incidence of thyroid cancer in Fukushima.

METHODS

We designed a prospective study with 300,473 participants aged 18 years or younger, who underwent thyroid examinations from October 2011. Follow-up surveys were conducted through June 2017, and 245,530 participants (123,480 men and 122,050 women, 82% follow-up) received follow-up examinations. Fukushima Prefecture was divided into five areas based on individual external radiation dose. We calculated relative risks and 95% confidence intervals (CIs) for thyroid cancer in each area, with area of lowest dose as reference, using age-adjusted Poisson regression models. We also calculated risks associated with overweight and obesity.

RESULTS

The incidence per 100,000 for Groups A (highest dose), B, C, D, and E (lowest dose) were 13.5, 19.2, 17.3, 9.0, and 8.3, respectively. Compared with Group E, the age-adjusted risks (95% CIs) were 1.62 (0.59, 4.47) for group A, 2.32 (0.86, 6.24) for group B, 2.21 (0.82, 5.94) for group C, and 1.02 (0.36, 2.86) for group D. Obesity was positively associated with thyroid cancer incidence; the multivariable-adjusted risk of thyroid cancer was 2.23 (1.01, 4.90) for obese individuals compared with nonobese individuals.

CONCLUSION

Regional differences in radiation dose were not associated with increased risk of thyroid cancer among children in Fukushima within 4 to 6 years after the nuclear power plant accident. Obesity may be an important factor for further follow-up in Fukushima.

Measuring individual external doses of Tokyo Electric Power Company Holdings employees living in Fukushima prefecture

Since the accident at Fukushima Daiichi Nuclear Power Plant, individual external doses of residents have been investigated. To accurately analyse survey data, a variety of information, including the activity patterns of many residents, needs to be integrated. However, such large-scale surveys have not yet been conducted and actual individual external doses in Fukushima are unclear. In this study, the individual external doses of approximately 300 Tokyo Electric Power Company Holdings employees, who live and work in Fukushima Prefecture outside the Fukushima Daiichi Nuclear Power Plant, were measured. The employees carried GPS loggers and personal dosimeters capable of measuring dose in counts per minute. The employees' individual external doses were compared along with their activity patterns. It was found that the annual additional individual external dose estimated based upon actual measurements was 1 mSv or less, and the influence on the individual external dose was also revealed.

Nested matched case control study for the Japan Fukushima Health Management Survey's first full-scale (second-round) thyroid examination

Since Fukushima nuclear accident in 2011, thyroid ultrasound examinations have been conducted. The first full-scale examination detected 71 thyroid-cancer cases. This study examined whether radiation exposure was associated with thyroid-cancer incidence.Subjects were participants in the baseline screening and newborns during the 2011 fiscal year. Under nested matched case-control study design, 10 controls per each case were selected by matching the age, sex, baseline screening results, and interval between examinations. With 3 dose levels of external radiation: 1.3 + mSv (upper), 0.8 to 1.3 (middle), and 0.0 to 0.8 (reference), we applied 2 logistic models adjusting for 3 participation-proportions (primary, secondary, and fine-needle aspiratory cytology), overweight, and the B-result of baseline screening (Model 1), and past medical history, family history of thyroid cancer, and frequencies of eating seafood and seaweed in addition to the parameters in Model 1 (Model 2). We examined each model in 3 ways: (a) excluding subjects with a missing radiation exposure dose; and substituting (b1) median or (b2) mean dose of the municipality with missing dose.Odds ratios (ORs) of middle-dose exposure were (a) 1.35 (0.46-3.94), (b1) 1.55 (0.61-3.96), and (b2) 1.23 (0.50-3.03) for Model 1, and (a) 1.18 (0.39-3.57), (b1) 1.31 (0.49-3.49), and (b2) 1.02 (0.40-2.59) for Model 2. For upper-dose exposure, similar results were obtained. Past medical history was significantly associated (odds ratio  = 2.04-2.08) with both (b1) and (b2) in Model 2.No significant associations were obtained between the external radiation exposure and thyroid-cancer incidence.

"Living in Contaminated Areas"-Consideration of Different Perspectives

Following large-scale nuclear power plant accidents such as those that occurred at Chernobyl (Ukraine) in 1986 and Fukushima Daiichi (Japan) in 2011, large populations are living in areas containing residual amounts of radioactivity. As a key session of the ConRad conference, experts were invited from different disciplines to provide state-of-the-art information on the topic of "living in contaminated areas." These experts provided their different perspectives on a range of topics including radiation protection principles and dose criteria, environmental measurements and dose estimation, maintaining decent living and working conditions, evidence of health risks, and social impact and risk communication. A short summary of these different perspectives is provided in this paper.

AGE DEPENDENCE OF INDIVIDUAL EXTERNAL DOSES IN AN EARLY STAGE AFTER THE FUKUSHIMA NUCLEAR ACCIDENT

Individual external doses for the first 4 months after the Fukushima accident have been estimated by the 'Basic Survey' of the Fukushima Health Management Survey. On the other hand, the UNSCEAR 2013 report presented the first-year effective dose due to external radiation for each municipality in nonevacuated areas of Fukushima Prefecture. In this study, the doses estimated by the Basic Survey were averaged for each of three age groups (infants, 0-5 y; children, 6-15 y; and adults, >16 y), in accordance with the categories adopted by the UNSCEAR report. The average dose ratios (infants/adults and children/adults) obtained from the Basic Survey were 1.08 and 1.06 for nonevacuated areas, respectively. These were smaller than the estimation by the UNSCEAR report (1.7 and 1.4, respectively). Three factors (body size factor, location factor and occupancy factor) were discussed and the location and occupancy factors were likely to be reasons for the difference.

Characteristics of Disaster-Related Suicide in Fukushima Prefecture After the Nuclear Accident

Abstract.Background: Suicide is a major concern after the 2011 earthquake and nuclear accident in Fukushima. Aims: This study delineates characteristics of the disaster-related suicides in Fukushima. Method: Data provided by the Fukushima Prefectural Police and data published by the Fukushima or Japanese Government were analyzed. Numbers of disaster-related suicides and evacuees were compared among the three prefectures affected. Age, sex, occupation, and means for disaster-related suicides in Fukushima were compared with overall suicides in Fukushima or Japan. History of medical treatment, changes in job and family structure after the disaster, and signs of contemplation were examined within the disaster-related suicides of Fukushima. Results: While other prefectures have experienced a drop in disaster-related suicides, Fukushima has not. Age-standardized disaster-related suicide rates were remarkably higher in men than in women. Moreover, disaster-related suicide rates in Fukushima were higher in women in their 50s and 80s as compared with overall suicide rates in Fukushima or Japan. Limitations: No detailed comparisons were made between disaster-related and non-disaster-related suicides. Conclusion: Disaster-related suicide rates were higher in men than in women. Also, it was found that the disaster-related suicide rates of elderly women were higher compared with overall suicide rates in Japan and Fukushima. In addition, many who died by suicide showed signs of contemplation before the attempt and had started psychiatric treatment. Improvement of suicide risk assessment skills for mental health professionals and gatekeeper training among residents will be essential to prevent disaster-related suicides.

Relationship between environmental radiation and radioactivity and childhood thyroid cancer found in Fukushima health management survey

Environmental radioactive contamination caused by the Fukushima Dai-ichi Nuclear Power Plant accident has aroused great concern regarding a possible increase in the incidence of childhood thyroid cancer. The ultrasound examinations were conducted immediately after the accident as part of the Fukushima Health Management Survey (FHMS), which is divided into the preliminary baseline survey (PBLS) and the full-scale survey (FSS). Some of their outcomes are reported regularly and made available to the public. We have detailed measurements of the air-dose rates and radioactive elements in soil in many places all over the Fukushima prefecture. To study the dose-response relationship, we begin with the assumption that the external and internal doses are correlated with the air-dose rate and the amount of ¹³¹I in soil, respectively. We then investigate the relationship between these estimated doses and the PBLS and FSS thyroid cancer cases. Our analysis shows that the dose-response curve with the FSS data clearly differs from that with the PBLS data. Finally, we consider the potential mitigating effects of evacuation from highly contaminated areas in both external and internal exposure scenarios.

Low dose of external exposure among returnees to former evacuation areas: a cross-sectional all-municipality joint study following the 2011 Fukushima Daiichi nuclear power plant incident

There is little information on the radiation dose levels of returnees to areas once designated as legal no-go zones, after evacuation orders were lifted subsequent to the 2011 Fukushima Daiichi nuclear power plant incident. This study used individual radiation dosimeter monitoring and a location history survey to conduct the most recent dose assessment of external exposure among returnees to former no-go zones. We specifically determined correlation and agreement between external doses and the air dose rate in residential areas and quantified both uncertainty and population variability of the observed data using Monte Carlo (MC) simulation methods. A total of 239 voluntary participants across ten municipalities were analysed; their representativeness of all affected municipal populations was confirmed in terms of air dose rate distribution in residential areas. We found that individual doses were statistically significantly correlated with the air dose rate based on government airborne monitoring. This implies that airborne monitoring can provide sufficient information for understanding dose levels among such returnees. The MC simulations demonstrated that the mean of the annual dose in 2019 (including natural background doses) was 0.93 (95% uncertainty interval 0.53-1.76) mSv, with limited variation between municipalities. As of 2019, this implies that doses from external exposure were very low among returnees and would be associated with a very low likelihood of physical effects according to current scientific consensus. However, these results should be taken with caution due to several study limitations, including selection and participation biases. Regardless, its findings will enhance societal debates about how both individual-dose and government airborne monitoring practices should operate in the future and how the government can improve the public outlook for radiation doses in incident-affected areas.

Reconstruction of residents' thyroid equivalent doses from internal radionuclides after the Fukushima Daiichi nuclear power station accident

There is concern among residents that their children might suffer from thyroid cancer in the near future after the Fukushima Daiichi nuclear power station (FDNPS) accident. However, the demographic and geographical distribution of thyroid equivalent doses was not thoroughly evaluated, and direct thyroid measurements were conducted only for 1,200 children, whose individual thyroid doses were assessed on the basis of those measurements accounting for the dynamics of radioiodine intake. We conducted hierarchical clustering analyses of 100 or 300 randomly sampled behavioural questionnaire sheets of children from each of seven municipalities in the evacuation area to reconstruct evacuation scenarios associated with high or low exposures to plumes. In total 896 behaviour records in the Fukushima Health Management Survey were analysed to estimate thyroid equivalent doses via inhalation, using a spatiotemporal radionuclides concentration database constructed by atmospheric dispersion simulations. After a decontamination factor for sheltering and a modifying factor for the dose coefficient-to reflect lower iodine uptake rate in Japanese-were applied, estimated thyroid equivalent doses were close to those estimated from direct thyroid measurement. The median and 95th percentile of thyroid equivalent doses of 1-year-old children ranged from 0.6 to 16 mSv and from 7.5 to 30 mSv, respectively. These results are useful for future epidemiological studies of thyroid cancer in Fukushima.

Cost of fear and radiation protection actions: Washington County, Utah and Fukushima, Japan {Comparing case histories}

Purpose: The purpose of this manuscript is to evaluate the role of regulatory limits and regulatory action on the total impact of nuclear contamination and accidents. While it is important to protect the public from excessive radiation exposures it is also critical to weigh the damage done by implementing regulations against the benefits produced. Two cases: Actions taken as a result of radioactive fallout in Washington County, Utah in 1953 from the atomic bomb testing in Nevada, and the actions implemented post release of radioactive materials into the environment from the damaged nuclear power reactor at Fukushima, Japan, are compared.Materials and methods: The Washington County radiation exposures and doses, resulting from the Nevada nuclear weapons tests, were taken from published reports, papers, and historical records. The protective actions taken were reviewed and reported. Recent publications were used to define the doses following Fukushima. The impact and/or results of sheltering only versus sheltering/evacuation of Washington County and Fukushima are compared.Results: The radiation dose from the fallout in Washington County from the fallout was almost 2-3 three times the dose in Japan, but the regulatory actions were vastly different. In Utah, the minimal action taken, e.g. sheltering in place, had no major impact on the public health or on the economy. The actions in Fukushima resulted in major negative impact precipitated through the fear generated. And the evacuation. The results had adverse human health and wellness consequences and a serious impact on the economy of the Fukushima region, and all of Japan.Conclusions: When evacuation is being considered, great care must be taken when any regulatory actions are initiated based on radiation limits. It is necessary to consider total impact and optimize the actions to limit radiation exposure while minimizing the social, economic, and health impacts. Optimization can help ensure that the protective measures result in more good than harm. It seems clear that organizations who recommend radiation protection guidelines need to revisit the past and current guides in light of the significant Fukushima experience.

Reassessment of Internal Thyroid Doses to 1,080 Children Examined in a Screening Survey after the 2011 Fukushima Nuclear Disaster

The dose reconstruction of populations potentially affected by the accident at the Fukushima Daiichi nuclear power plant in March 2011 is of great importance. However, it has been difficult to assess internal thyroid doses to Fukushima residents (mainly from their intake of I) due to the lack of direct measurements. For the residents, only about 1,300 data points related to I are available, and 1,080 of the data points were obtained from the screening campaign that was conducted by the Nuclear Emergency Response Local Headquarters at the end of March 2011 in Kawamata Town, Iwaki City, and Iitate Village. Here, we reassessed thyroid doses to 1,080 subjects aged ≤15 y old using new age-specific conversion factors to determine I thyroid contents from net signals of the devices used, with consideration for the possible uncertainty related to the measurements. The results demonstrated that thyroid equivalent doses to the subjects were <30 mSv (excluding outliers). We also demonstrate dose distributions of each age group from the above three municipalities and those of subjects from Minamisoma City and Fukushima City. One of the findings was that the I intake was similar among different age groups in each of the three municipalities. This was consistent with the assumption that ingestion was a dominant route of intake rather than inhalation. The range of thyroid doses to Iitate Village residents was similar to that to Iwaki City residents even though the I concentration in tap water was much higher in Iitate Village than Iwaki City. The range of thyroid doses to Minamisoma City residents was similar to that to Iitate Village and Iwaki City residents, and the range for Fukushima City residents was smallest among the five municipalities. Since the major route of intake has remained unclear, this paper presents the plausible upper and lower thyroid doses, between which the actual doses are thought to mostly exist, based on two intake scenarios: single inhalation and repeated ingestion. Further research is thus necessary to extract useful evidence from the individual evacuation behaviors for improving the present internal thyroid dose assessment.

The latest update on individual external doses in an early stage after the Fukushima nuclear accident

Following the Fukushima Daiichi Nuclear Power Plant accident, a survey for estimating individual external doses for the first 4 months after the accident was started, and it remains ongoing. Since the authors' previous paper, 44 605 new dose estimates have been made. The new dose estimates increase the number of dose estimates to 465 999 and are reported in this note. Since the previous paper, most of the recently collected responses have been gotten through public relations activities to encourage responses across the prefecture. Thus, recent respondents might be biased ('selection bias'). Also, the dose estimates were based on self-administered responses about personal behaviour, which relied on memories of residents. In this respect, incorrect behaviour records possibly resulted as memories have faded over time ('recall bias'). However, the effects of these biases on dose distribution on a whole-prefecture basis seemed to be small.

Incidence of Thyroid Cancer Among Children and Young Adults in Fukushima, Japan, Screened With 2 Rounds of Ultrasonography Within 5 Years of the 2011 Fukushima Daiichi Nuclear Power Station Accident

Importance

Ultrasonographic (US) screening for thyroid cancer was performed in the Fukushima Health Management Survey after the 2011 Fukushima Daiichi nuclear power station accident. Clinical characteristics of thyroid cancers screened by US among children and young adults during the first 5 years after the accident were analyzed.

Objectives

To evaluate the number of detected thyroid cancers by age group within 5 years of the Fukushima Daiichi nuclear power station accident and to compare the basic clinical characteristics and demographic patterns in first- and second-round examinations.

Design, Setting, and Participants

In this observational study, 324 301 individuals 18 years or younger at the time of accident were included. Patients received a cytologic diagnosis of malignant or suspected malignant thyroid cancer during the first (fiscal years 2011-2013) or second round (fiscal years 2014-2015) of screening. Number of detected cases of cancer was evaluated, correcting for the number of examinees by age group at the time of the accident and for the incidence of detected cancers according to age group at the time of the screening (age groups were divided into 3-year intervals). Results were compared using the age-specific incidence of unscreened cancers from a national cancer registry.

Main Outcomes and Measures

Clinical baseline characteristics of the patients and the age-specific number and incidence of thyroid cancers detected during the second round.

Results

Among 299 905 individuals screened in the first round (50.5% male; mean [SD] age at screening, 14.9 [2.6] years), malignant or suspected thyroid cancer was diagnosed in 116. Among 271 083 individuals screened in the second round (50.4% male; age at screening, 12.6 [3.2] years), malignant or suspected thyroid cancer was diagnosed in 71. The most common pathologic diagnosis in surgical cases was papillary thyroid cancer (149 of 152 [98.0%]). The distribution pattern by age group at the time of the accident, where the number of detected thyroid cancer cases was corrected by the number of examinees, increased with older age in both screening rounds. This demographic pattern was similar between the first and second examinations. The distribution pattern of the incidence rate by age group at the time of screening in the second round also increased with older age. The incidence rate detected by screening was 29 cases per 100 000 person-years for those aged 15 to 17 years, 48 cases per 100 000 person-years for those aged 18 to 20 years, and 64 cases per 100 000 person-years for those aged 21 to 22 years.

Conclusions and Relevance

Large-scale mass US screening of young people resulted in the diagnosis of a number of thyroid cancers, with no major changes in overall characteristics within 5 years of the 2011 Fukushima nuclear power station accident. These results suggest that US screening can identify many detectable cancers from a large pool of nonclinical and subclinical thyroid cancers among individuals of a relatively young age, in an age-dependent manner.

External dose evaluation based on detailed air dose rate measurements in living environments

A method was devised to estimate the realistic external doses of residents expected to return to their homes after evacuation orders are lifted. For 196 residents expected to return to six towns and villages, surveys were administered in FY 2014-2016. After interviewing residents about their expected life patterns after their return, detailed air dose rate measurements were taken along their reported personal routes representing patterns of movement in their daily life. The maximum and average annual additional external effective dose were estimated at 4.9 mSv and 0.86 mSv, respectively. Although the mean values and dispersion of external effective doses differed depending on the level of evacuation, for 93.3% of all residents, the estimated annual additional external effective doses were less than 2 mSv. Measuring air dose rates inside houses was found to be important to obtain a realistic evaluation of the external exposure dose because our research revealed that the average time spent indoors was 87% of the total living time. Moreover, the average exposure dose at home accounted for 66.8% of the annual exposure dose.

Radiation doses and decontamination effects in Minamisoma city: airborne and individual monitoring after the Fukushima nuclear accident

After the Fukushima accident, airborne monitoring was implemented to measure airborne radiation. We examined the relationships between airborne and individual radiation monitoring and clarified the use of airborne monitoring to evaluate the effects of decontamination on residents' received doses. We used the air dose rate data from four airborne monitors conducted between 2013 and 2016, and the dose data from four individual monitors (in which a total of 18 392 adults and 3650 children participated), conducted in Minamisoma City during the same period. We examined the Pearson correlation coefficients between the airborne and individual monitoring data and estimated exposure ratios (ERs; ratios of individual dose to air dose rates) among adults and children. We also estimated the effects of decontamination on residents' doses based on airborne monitoring data, adjusting this for timing and dosing through propensity score matching, which were then compared to individual monitoring data. There were significant correlations between airborne and individual monitoring doses among adults and children, and more than 80% of residents showed a good estimation-observation agreement within a factor of two. The median of ERs was 0.304 and 0.250 among adults and children, respectively. There was a significant difference between the two. Effects of decontamination on residents' doses estimated from airborne monitoring were significantly lower than those estimated from individual monitoring. These findings suggest that airborne monitoring can be used to estimate representative radiation doses within residential areas. It may be a useful tool for enhancing communication among stakeholders and supporting individual and policy decisions; however, it is less sensitive for evaluating individual effects of decontamination than individual monitoring. Combined use of airborne and individual monitoring also showed a lower median of ERs in children than in adults and in a Japanese government's model, possibly due to prioritised decontamination for children and differences between their behavioral patterns.

COMPARATIVE STUDY ON PERFORMANCE OF VARIOUS ENVIRONMENTAL RADIATION MONITORS

After the Fukushima Daiichi Nuclear Power Plant accident, the radiation dose for first responders was not evaluated accurately due to lack of the monitoring data. It has been important to evaluate a radiation dose for workers in emergency response at a nuclear accident. In this study, a new device which can evaluate both of external and internal exposure doses was developed and the performance of various environmental radiation monitors including commercially available monitors were tested and compared from the viewpoint of an environmental monitoring at emergency situation. Background counts of the monitors and the ambient dose equivalent rate were measured in Fukushima Prefecture. The detection limit for beta particles was evaluated by the method of ISO11929. The sensitivity for gamma-rays of the dust monitor using a ZnS(Ag) and a plastic scintillator was high, but that of the external exposure monitor using a silicon photodiode with CsI(Tl) crystal was relatively low. The detection limit ranged 190-280 Bq m-3 at 100 μSv h-1, exceeding the detection limit of 100 Bq m-3 in the minimum requirement by the National Regulation Authority in Japan. Use of the shielding with lead is necessary to achieve the minimum requirement. These results indicate that the dust monitor using a ZnS(Ag) scintillator and a plastic scintillator is suitable for the external exposure monitor and the developed internal exposure monitor is for the internal exposure monitor at emergency situation among the evaluated monitors. In the future study, the counting efficiency, the relative uncertainty and the performance of the detection for alpha particles will be evaluated, and it will be considered which type of a monitor is suitable after taking the portability into account.

Lingering health-related anxiety about radiation among Fukushima residents as correlated with media information following the accident at Fukushima Daiichi Nuclear Power Plant

Following the March 2011 accident at Fukushima Daiichi Nuclear Power Plant, many residents of Fukushima have faced anxieties about the health impacts of radiation exposure. Considering that source of information may influence resident anxiety, this study aimed to elucidate the correlation between the two. In addition, a health literacy query was included to examine a possible relationship between anxiety and health literacy skills. A mail survey was conducted in August 2016 among 2000 residents of Fukushima Prefecture aged 20 to 79 years. Survey items included questions about current health anxieties caused by radiation, trusted sources of information about radiation, and media used to obtain information on radiation. The survey valid response rate was 43.4%. Results of multiple linear regression analysis revealed that anxiety was significantly higher for the groups indicating “trust in citizen groups” and “use of internet sites.” Anxiety was significantly lower for the groups indicating “trust in government ministries,” “trust in local government,” and “use of local broadcast television.” Also anxiety was significantly lower for groups with higher health literacy. It was found that the significant relationship to anxiety varies depending on the sources of trust and media used. There is a possibility that this was caused by the difference between the contents of each information and media reports. In preparation for any future nuclear accident, government may consider action to improve the media literacy of residents. In addition, improving health literacy of both the recipient and the sender of information can improve access to information and thereby safeguard the health and well-being of the public.

A Probabilistic Approach to Assess External Doses to the Public Considering Spatial Variability of Radioactive Contamination and Interpopulation Differences in Behavior Pattern

Dose assessment is an important issue from the viewpoints of protecting people from radiation exposure and managing postaccident situations adequately. However, the radiation doses received by people cannot be determined with complete accuracy because of the uncertainties and the variability associated with any process of defining individual characteristics and in the dose assessment process itself. In this study, a dose assessment model was developed based on measurements and surveys of individual doses and relevant contributors (i.e., ambient dose rates and behavior patterns) in Fukushima City for four population groups: Fukushima City Office staff, Senior Citizens' Club, Contractors' Association, and Agricultural Cooperative. In addition, probabilistic assessments were performed for these population groups by considering the spatial variability of contamination and interpopulation differences resulting from behavior patterns. As a result of comparison with the actual measurements, the assessment results for participants from the Fukushima City Office agreed with the measured values, thereby validating the model and the approach. Although the assessment results obtained for the Senior Citizens' Club and the Agricultural Cooperative differ partly from the measured values, by addressing further considerations in terms of dose reduction effects due to decontamination and the impact of additional exposure sources in agricultural fields, these results can be improved. By contrast, the measurements obtained for the participants from the Contractors' Association were not reproduced well in the present study. To assess the doses to this group, further investigations of association members' work activities and the related dose reduction effects are needed.

Low-dose radiation from A-bombs elongated lifespan and reduced cancer mortality relative to un-irradiated individuals

The US National Academy of Sciences (NAS) presented the linear no-threshold hypothesis (LNT) in 1956, which indicates that the lowest doses of ionizing radiation are hazardous in proportion to the dose. This spurious hypothesis was not based on solid data. NAS put forward the BEIR VII report in 2006 as evidence supporting LNT. The study described in the report used data of the Life Span Study (LSS) of A-bomb survivors. Estimation of exposure doses was based on initial radiation (5%) and neglected residual radiation (10%), leading to underestimation of the doses. Residual radiation mainly consisted of fallout that poured down onto the ground along with black rain. The black-rain-affected areas were wide. Not only A-bomb survivors but also not-in-the-city control subjects (NIC) must have been exposed to residual radiation to a greater or lesser degree. Use of NIC as negative controls constitutes a major failure in analyses of LSS. Another failure of LSS is its neglect of radiation adaptive responses which include low-dose stimulation of DNA damage repair, removal of aberrant cells via stimulated apoptosis, and elimination of cancer cells via stimulated anticancer immunity. LSS never incorporates consideration of this possibility. When LSS data of longevity are examined, a clear J-shaped dose-response, a hallmark of radiation hormesis, is apparent. Both A-bomb survivors and NIC showed longer than average lifespans. Average solid cancer death ratios of both A-bomb survivors and NIC were lower than the average for Japanese people, which is consistent with the occurrence of radiation adaptive responses (the bases for radiation hormesis), essentially invalidating the LNT model. Nevertheless, LNT has served as the basis of radiation regulation policy. If it were not for LNT, tremendous human, social, and economic losses would not have occurred in the aftermath of the Fukushima Daiichi nuclear plant accident. For many reasons, LNT must be revised or abolished, with changes based not on policy but on science.

Experiences of Population Monitoring Using Whole-Body Counters in Response to the Fukushima Nuclear Accident

Whole-body counter measurements of residents of Fukushima Prefecture have been extensively performed after the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. These measurements have demonstrated that the levels of internal contamination with radioactive cesium (Cs and Cs) in the residents are very low. This article provides an overview of and lessons learned from these whole-body counter measurements with emphasis on the technical problems encountered, and it discusses the effective use of whole-body counters for assessing the internal thyroid doses of individuals when direct measurements of I in the thyroid are difficult or impossible to implement for the total affected population in a short time after a nuclear reactor accident. The application of this dose reconstruction method requires determining the intake ratio of I to cesium isotopes at appropriate times and considers the short biological half-lives of cesium isotopes, in particular for children.

Induction of somatic mutations by low-dose X-rays: the challenge in recognizing radiation-induced events

It is difficult to distinguish radiation-induced events from spontaneous events during induction of stochastic effects, especially in the case of low-dose or low-dose-rate exposures. By using a hypersensitive system for detecting somatic mutations at the HPRT1 locus, we investigated the frequency and spectrum of mutations induced by low-dose X-rays. The mutant frequencies induced by doses of >0.15 Gy were statistically significant when compared with the spontaneous frequency, and a clear dose dependency was also observed for mutant frequencies at doses of >0.15 Gy. In contrast, mutant frequencies at doses of <0.1 Gy occurred at non-significant levels. The mutation spectrum in HPRT-deficient mutants revealed that the type of mutations induced by low-dose exposures was similar to that seen in spontaneous mutants. An apparent change in mutation type was observed for mutants induced by doses of >0.2 Gy. Our observations suggest that there could be a critical dose for mutation induction at between 0.1 Gy and 0.2 Gy, where mutagenic events are induced by multiple DNA double-strand breaks (DSBs). These observations also suggest that low-dose radiation delivered at doses of <0.1 Gy may not result in DSB-induced mutations but may enhance spontaneous mutagenesis events.

Causes and Radiological Consequences of the Chernobyl and Fukushima Nuclear Accidents

In this paper, the causes and the radiological consequences of the explosion of the Chernobyl reactor occurred at 1:23 a.m. (local time) on Apr. 26, 1986, and of the Fukushima Daiichi nuclear disaster following the huge Tsunami caused by the Great East Japan earthquake at 2.46 p.m. (local time) on Mar. 11, 2011 are discussed. The need for better severe accident management (SAM), and severe accident management guidelines (SAMGs), are essential in order to increase the safety of the existing and future operating nuclear power plants (NPPs). In addition to that, stress tests should, on a regular basis, be performed to assess whether the NPPs can withstand the effects of natural disasters and man-made failures and actions. The differences in safety preparations at the Chernobyl and Fukushima Daiichi will therefore be presented, as well as recommendations concerning improvements of safety culture, decontamination, and disaster planning. The need for a high-level national emergency response system in case of nuclear accidents will be discussed. The emergency response system should include fast alarms, communication between nuclear power plants, nuclear power authorities and the public people, as well as well-prepared and well-established evacuation plans and evacuation zones. The experiences of disaster planning and the development of a new improved emergency response system in Japan will also be presented together with the training and education program, which have been established to ensure that professional rescue workers, including medical staff, fire fighters, and police, as well as the normal populations including patients, have sufficient knowledge about ionizing radiation and are informed about the meaning of radiation risks and safety.

Effect of Radiological Countermeasures on Subjective Well-Being and Radiation Anxiety after the 2011 Disaster: The Fukushima Health Management Survey

After the Fukushima Daiichi Nuclear Power Station accident in 2011, concerns about radiation exposure and decline in subjective well-being have been reported. To tackle these problems, various countermeasures in relation to radiation have been implemented. In this study, we comprehensively evaluated the effects of radiological countermeasures on subjective well-being (e.g., satisfaction with life (SWL) and emotional well-being) and radiation anxiety, through a questionnaire survey targeting Fukushima residents (N = 1023). Propensity scores matching was applied to evaluate significant effects of radiological countermeasures on subjective well-being and radiation anxiety. Among the radiological countermeasures, thyroid examination, whole body counter, and air dose monitoring showed the highest proportions of participation, utilization, and useful evaluation, suggesting a high degree of public attention focused on these countermeasures. The basic survey was associated with significant increases in SWL and self-rated health (SH). Thyroid examination was significantly associated with not only a reduction in radiation anxiety but also an increase of emotional stress, suggesting the importance of careful design of system and detailed communication. Food inspection was associated with deterioration in SH. Those who utilized explanatory meetings showed increases in sadness, worry, and radiation anxiety, indicating that additional attention is required of the experts and authorities involved in explanatory meetings.

Lessons from Fukushima: Latest Findings of Thyroid Cancer After the Fukushima Nuclear Power Plant Accident

The increase in risk for late-onset thyroid cancer due to radiation exposure is a potential health effect after a nuclear power plant accident mainly due to the release of radioiodine in fallout. The risk is particularly elevated in those exposed during infancy and adolescence. To estimate the possibility and extent of thyroid cancer occurrence after exposure, it is of utmost importance to collect and analyze epidemiological information providing the basis for evaluation of radiation risk, and to consider radiobiology and molecular genetics. In this regard, the dose-response of cancer risk, temporal changes in the rates of thyroid cancer, its histopathological types and subtypes, and frequency of underlying genetic abnormalities are important. At present, however, it is difficult or impossible to distinguish radiation-induced thyroid cancer from spontaneous/sporadic thyroid cancer because molecular radiation signatures, biomarkers of radiation exposure, or genetic factors specific to radiation-induced cancer have not yet been identified. The large-scale ultrasound screening in Fukushima Prefecture of Japan demonstrated a high detection rate of thyroid cancer in young individuals, revealing 116 and 71 cases in the first and second rounds, respectively, among the same cohort of approximately 300,000 subjects. These findings raised concerns among residents and the public that it might be due to putative exposure to radiation from the accident at Fukushima Daiichi Nuclear Power Plant. This review summarizes evaluations by international organizations and reviews scientific publications by the authors and others on childhood thyroid cancer, especially those relevant to radiation, including basic studies on molecular mechanisms of thyroid carcinogenesis. Clinical details are also provided on surgical cases in Fukushima Prefecture, and the effect of thyroid ultrasound screening is discussed. Correct understanding of issues relating to radiation and the thyroid are essential for interpretation of thyroid cancer in Fukushima.

Representativeness of individual external doses estimated for one quarter of residents in the Fukushima Prefecture after the nuclear disaster: the Fukushima Health Management Survey

After the Fukushima Dai-ichi Nuclear Power Plant accident, the Fukushima Health Management Survey (FHMS) was launched. The Basic Survey, a component of FHMS, is a questionnaire used to survey residents across the Fukushima Prefecture about their behaviour in the first 4 months after the accident. The questionnaire findings are used to determine individual external doses by linking behaviour data to a computer programme with daily gamma ray dose rate maps, drawn after the accident. Through 30 June 2015, the response rate was only 27.2% (558 550 population), indicating that the findings might not be generalisable because of poor representativeness of the population. The objective of this study was to clarify if the data from the FHMS Basic Survey were representative of the entire population, by conducting a new survey to compare the external doses between non-respondents and respondents in the previous survey. A total of 5350 subjects were randomly selected from 7 local regions of Fukushima Prefecture. An interview survey was conducted with the non-respondents to the FHMS Basic Survey. A total of 990 responses were obtained from the previous non-responders by interview survey. For the regions Kempoku, Kenchu, Kennan, Aizu, Minami-Aizu, Soso, and Iwaki, differences in mean effective dose (95% confidence interval) in mSv between the non-responders and previous responders were 0.12 (0.01-0.23), -0.09 (-0.21-0.03), -0.06 (-0.18-0.07), 0.05 (-0.04-0.14), 0.01 (-0.01-0.02), 0.09 (0.01-0.17), 0.09 (0.00-0.17), respectively. The differences fall neither within the interval (-∞, -0.25) nor within the interval (0.25, ∞). These findings imply that mean effective doses between the previous and new respondents were not different, with a significantly indifferent region of 0.25 mSv according to equivalence tests. The present study indicates that the dose distribution obtained from about one-quarter of Fukushima residents represents the dose distribution for the entire Fukushima Prefecture.