Radiation-related brain damage and growth retardation among the prenatally exposed atomic bomb survivors

CDC Division of Reproductive Health's Emergency Preparedness Resources and Activities for Radiation Emergencies: Public Health Considerations for Women's Reproductive Health

Pregnant, postpartum, and lactating people, and infants have unique needs during public health emergencies, including nuclear and radiological incidents. This report provides information on the CDC Division of Reproductive Health's emergency preparedness and response activities to address the needs of women of reproductive age (aged 15-49 years), people who are pregnant, postpartum, or lactating, and infants during a radiation emergency. Highlighted preparedness activities include: (1) development of a quick reference guide to inform key questions about pregnant, postpartum, and lactating people, and infants during radiation emergencies; and (2) exercising the role of reproductive health experts during nuclear and radiological incident preparedness activities.

Neurocognitive Function in Aged Survivors Exposed to Atomic Bomb Radiation In Utero: The Radiation Effects Research Foundation Adult Health Study

Although some adverse effects on neurocognitive function have been reported in children and adolescents irradiated prenatally during the atomic bombings and the Chernobyl nuclear accident, little information is available for effects on the elderly. Here we evaluate the effects of prenatal exposure to atomic bomb radiation on subjective neurocognitive function in aged survivors. To evaluate neurocognitive impairment, we mailed the Neurocognitive Questionnaire (NCQ), a self-administered scale, to prenatally exposed survivors, including clinic visitors and non-visitors at the time of the 2011 and 2013 Adult Health Study (AHS) examinations. We received replies from 444 individuals (mean age, 66.9 ± 0.6 years). After adjusting for sex, city, and educational background, we found no significant effects of radiation, clinic visit, or interaction between radiation and clinic visit on the scores of the 4 NCQ factors of metacognition, emotional regulation, motivation/organization, and processing speed. Even in analyses considering gestational age at the time of the bombings, none of the 4 NCQ factor scores was related to maternal uterine dose. There remains the limitation that this study consisted of healthy survivors, but we found no significant radiation effect on late-life cognition in people prenatally exposed to atomic bomb radiation.

DNA damage and repair: underlying mechanisms leading to microcephaly

DNA-damaging agents and endogenous DNA damage constantly harm genome integrity. Under genotoxic stress conditions, the DNA damage response (DDR) machinery is crucial in repairing lesions and preventing mutations in the basic structure of the DNA. Different repair pathways are implicated in the resolution of such lesions. For instance, the non-homologous DNA end joining and homologous recombination pathways are central cellular mechanisms by which eukaryotic cells maintain genome integrity. However, defects in these pathways are often associated with neurological disorders, indicating the pivotal role of DDR in normal brain development. Moreover, the brain is the most sensitive organ affected by DNA-damaging agents compared to other tissues during the prenatal period. The accumulation of lesions is believed to induce cell death, reduce proliferation and premature differentiation of neural stem and progenitor cells, and reduce brain size (microcephaly). Microcephaly is mainly caused by genetic mutations, especially genes encoding proteins involved in centrosomes and DNA repair pathways. However, it can also be induced by exposure to ionizing radiation and intrauterine infections such as the Zika virus. This review explains mammalian cortical development and the major DNA repair pathways that may lead to microcephaly when impaired. Next, we discuss the mechanisms and possible exposures leading to DNA damage and p53 hyperactivation culminating in microcephaly.

Radiation risks and information needs of pregnant and lactating women

This a historical review and current information regarding risks and effects of ionizing radiation in the context of human pregnancy and in particular the information needed for pregnant women to understand the type and magnitude of risks placing them in a realistic context. Much of our understanding comes from early animal studies but has been supported by studies of human exposure to medical radiation, radiation accidents and nuclear weapons.

Radiology's Ionising Radiation Paradox: Weighing the Indispensable Against the Detrimental in Medical Imaging

Ionising radiation stands as an indispensable protagonist in the narrative of medical imaging, underpinning diagnostic evaluations and therapeutic interventions across an array of medical conditions. However, this protagonist poses a paradox - its inestimable service to medicine coexists with an undercurrent of potential health risks, primarily DNA damage and subsequent oncogenesis. The narrative of this comprehensive review unfurls around this intricate enigma, delicately balancing the indispensable diagnostic utility against the non-negotiable commitment to patient safety. In this critical discourse, the intricacies of ionising radiation are dissected, illuminating not only its sources but also the associated biological and health hazards. The exploration delves into the labyrinth of strategies currently deployed to minimise exposure and safeguard patients. By casting light on the scientific nuances of X-rays, computed tomography (CT), and nuclear medicine, it traverses the complex terrain of radiation use in radiology, to promote safer medical imaging practices, and to facilitate an ongoing dialogue about diagnostic necessity and risk. Through a rigorous examination, the pivotal relationship between radiation dose and dose response is elucidated, unravelling the mechanisms of radiation injury and distinguishing between deterministic and stochastic effects. Moreover, protection strategies are illuminated, demystifying concepts such as justification, optimisation, the As Low As Reasonably Achievable (ALARA) principle, dose and diagnostic reference levels, along with administrative and regulatory approaches. With an eye on the horizon, promising avenues of future research are discussed. These encompass low-radiation imaging techniques, long-term risk assessment in large patient cohorts, and the transformative potential of artificial intelligence in dose optimisation. This exploration of the nuanced complexities of radiation use in radiology aims to foster a collaborative impetus towards safer medical imaging practices. It underscores the need for an ongoing dialogue around diagnostic necessity and risk, thereby advocating for a continual reassessment in the narrative of medical imaging.

An integrative systems biology strategy to support the development of adverse outcome pathways (AOPs): a case study on radiation-induced microcephaly

Adverse Outcome Pathways (AOPs) are useful tools for assessing the potential risks associated with exposure to various stressors, including chemicals and environmental contaminants. They provide a framework for understanding the causal relationships between different biological events that can lead to adverse outcomes (AO). However, developing an AOP is a challenging task, particularly in identifying the molecular initiating events (MIEs) and key events (KEs) that constitute it. Here, we propose a systems biology strategy that can assist in the development of AOPs by screening publicly available databases, literature with the text mining tool AOP-helpFinder, and pathway/network analyses. This approach is straightforward to use, requiring only the name of the stressor and adverse outcome to be studied. From this, it quickly identifies potential KEs and literature providing mechanistic information on the links between the KEs. The proposed approach was applied to the recently developed AOP 441 on radiation-induced microcephaly, resulting in the confirmation of the KEs that were already present and identification of new relevant KEs, thereby validating the strategy. In conclusion, our systems biology approach represents a valuable tool to simplify the development and enrichment of Adverse Outcome Pathways (AOPs), thus supporting alternative methods in toxicology.

Influence of radiation exposure to delayed fetal growth in wild Japanese monkeys after the Fukushima accident

Wild Japanese monkeys (Macaca fuscata) were exposed to radiation after the Fukushima Daiichi nuclear accident in 2011. To clarify the biological effects of radiation exposure on their fetal growth, pregnant monkeys and their fetuses were analyzed. These animals were collected between 2008 and 2020 (before and after the accident in 2011) living in Fukushima City, approximately 70 km from the nuclear power plant. Multiple regression analyses were conducted with fetal body weight (FBW) and fetal head circumference (FHS) as objective variables, and maternal and fetal factors as explanatory variables. The maternal factors were relative exposure dose rate (REDR), age, body weight, body length, fat index, and parity. The fetal factors were crown ramp length (CRL) and sex. Multiple regression analyses showed that FBR and FHS growth were positively associated with CRL, maternal body length, and negatively associated with REDR. Since the relative growth of FBR and FHS to CRL decreased with increasing REDR, radiation exposure due to the nuclear accident may have contributed to the delayed fetal growth observed in Japanese monkeys.

Human development and reproduction in space-a European perspective

This review summarises key aspects of the first reproductive and developmental systems Science Community White Paper, supported by the European Space Agency (ESA). Current knowledge regarding human development and reproduction in space is mapped to the roadmap. It acknowledges that sex and gender have implications on all physiological systems, however, gender identity falls outside the scope of the document included in the white paper collection supported by ESA. The ESA SciSpacE white papers on human developmental and reproductive functions in space aim to reflect on the implications of space travel on the male and female reproductive systems, including the hypothalamic-pituitary-gonadal (HPG) reproductive hormone axis, and considerations for conception, gestation and birth. Finally, parallels are drawn as to how this may impact society as a whole on Earth.

Considerations of Medical Preparedness to Assess and Treat Various Populations During a Radiation Public Health Emergency

During a radiological or nuclear public health emergency, given the heterogeneity of civilian populations, it is incumbent on medical response planners to understand and prepare for a potentially high degree of interindividual variability in the biological effects of radiation exposure. A part of advanced planning should include a comprehensive approach, in which the range of possible human responses in relation to the type of radiation expected from an incident has been thoughtfully considered. Although there are several reports addressing the radiation response for special populations (as compared to the standard 18-45-year-old male), the current review surveys published literature to assess the level of consideration given to differences in acute radiation responses in certain sub-groups. The authors attempt to bring clarity to the complex nature of human biology in the context of radiation to facilitate a path forward for radiation medical countermeasure (MCM) development that may be appropriate and effective in special populations. Consequently, the focus is on the medical (as opposed to logistical) aspects of preparedness and response. Populations identified for consideration include obstetric, pediatric, geriatric, males, females, individuals of different race/ethnicity, and people with comorbidities. Relevant animal models, biomarkers of radiation injury, and MCMs are highlighted, in addition to underscoring gaps in knowledge and the need for consistent and early inclusion of these populations in research. The inclusion of special populations in preclinical and clinical studies is essential to address shortcomings and is an important consideration for radiation public health emergency response planning. Pursuing this goal will benefit the population at large by considering those at greatest risk of health consequences after a radiological or nuclear mass casualty incident.

A review on fetal dose in Radiotherapy: A historical to contemporary perspective

This paper aims to review on fetal dose in radiotherapy and extends and updates on a previous work¹ to include proton therapy. Out-of-field doses, which are the doses received by regions outside of the treatment field, are unavoidable regardless of the treatment modalities used during radiotherapy. In the case of pregnant patients, fetal dose is a major concern as it has long been recognized that fetuses exposed to radiation have a higher probability of suffering from adverse effects such as anatomical malformations and even fetal death, especially when the 0.1Gy threshold is exceeded. In spite of the low occurrence of cancer during pregnancy, the radiotherapy team should be equipped with the necessary knowledge to deal with fetal dose. This is crucial so as to ensure that the fetus is adequately protected while not compromising the patient treatment outcomes. In this review paper, various aspects of fetal dose will be discussed ranging from biological, clinical to the physics aspects. Other than fetal dose resulting from conventional photon therapy, this paper will also extend the discussion to modern treatment modalities and techniques, namely proton therapy and image-guided radiotherapy, all of which have seen a significant increase in use in current radiotherapy. This review is expected to provide readers with a comprehensive understanding of fetal dose in radiotherapy, and to be fully aware of the steps to be taken in providing radiotherapy for pregnant patients.

Development of an Adverse Outcome Pathway for radiation-induced microcephaly via expert consultation and machine learning

BACKGROUND

Brain development during embryogenesis and in early postnatal life is particularly complex and involves the interplay of many cellular processes and molecular mechanisms, making it extremely vulnerable to exogenous insults, including ionizing radiation (IR). Microcephaly is one of the most frequent neurodevelopmental abnormalities that is characterized by small brain size, and is often associated with intellectual deficiency. Decades of research span from epidemiological data on in utero exposure of the A-bomb survivors, to studies on animal and cellular models that allowed deciphering the most prominent molecular mechanisms leading to microcephaly. The Adverse Outcome Pathway (AOP) framework is used to organize, evaluate and portray the scientific knowledge of toxicological effects spanning different biological levels of organizations, from the initial interaction with molecular targets to the occurrence of a disease or adversity. In the present study, the framework was used in an attempt to organize the current scientific knowledge on microcephaly progression in the context of ionizing radiation (IR) exposure. This work was performed by a group of experts formed during a recent workshop organized jointly by the Multidisciplinary European Low Dose Initiative (MELODI) and the European Radioecology Alliance (ALLIANCE) associations to present the AOP approach and tools. Here we report on the development of a putative AOP for congenital microcephaly resulting from IR exposure based on discussions of the working group and we emphasize the use of a novel machine-learning approach to assist in the screening of the available literature to develop AOPs.

CONCLUSION

The expert consultation led to the identification of crucial biological events for the progression of microcephaly upon exposure to IR, and highlighted current knowledge gaps. The machine learning approach was successfully used to screen the existing knowledge and helped to rapidly screen the body of evidence and in particular the epidemiological data. This systematic review approach also ensured that the analysis was sufficiently comprehensive to identify the most relevant data and facilitate rapid and consistent AOP development. We anticipate that as machine learning approaches become more user-friendly through easy-to-use web interface, this would allow AOP development to become more efficient and less time consuming.

Revealing the Increased Stress Response Behavior through Transcriptomic Analysis of Adult Zebrafish Brain after Chronic Low to Moderate Dose Rates of Ionizing Radiation

Simple Summary

The increasing use of radiopharmaceuticals for medical diagnostics and radiotherapy raises concerns regarding health risks for both humans and the environment. Additionally, in the context of major nuclear accidents like in Chernobyl and Fukushima, very little is known about the effects of chronic exposure to low and moderate dose rates of ionizing radiation (IR). Many studies demonstrated the sensibility of the developmental brain, but little data exists for IR at low dose rates and their impact on adults. In this study, we characterized the molecular mechanisms that orchestrate stress behavior caused by chronic exposure to low to moderate dose rates of IR using the adult zebrafish model. We observed the establishment of a congruent stress response at both the molecular and individual levels.

Abstract

High levels of ionizing radiation (IR) are known to induce neurogenesis defects with harmful consequences on brain morphogenesis and cognitive functions, but the effects of chronic low to moderate dose rates of IR remain largely unknown. In this study, we aim at defining the main molecular pathways impacted by IR and how these effects can translate to higher organizational levels such as behavior. Adult zebrafish were exposed to gamma radiation for 36 days at 0.05 mGy/h, 0.5 mGy/h and 5 mGy/h. RNA sequencing was performed on the telencephalon and completed by RNA in situ hybridization that confirmed the upregulation of oxytocin and cone rod homeobox in the parvocellular preoptic nucleus. A dose rate-dependent increase in differentially expressed genes (DEG) was observed with 27 DEG at 0.05 mGy/h, 200 DEG at 0.5 mGy/h and 530 DEG at 5 mGy/h. Genes involved in neurotransmission, neurohormones and hypothalamic-pituitary-interrenal axis functions were specifically affected, strongly suggesting their involvement in the stress response behavior observed after exposure to dose rates superior or equal to 0.5 mGy/h. At the individual scale, hypolocomotion, increased freezing and social stress were detected. Together, these data highlight the intricate interaction between neurohormones (and particularly oxytocin), neurotransmission and neurogenesis in response to chronic exposure to IR and the establishment of anxiety-like behavior.

Risk of Adverse Pregnancy Outcomes in Young Women with Thyroid Cancer: A Systematic Review and Meta-Analysis

Simple Summary

This meta-analysis of 22 articles investigated whether thyroidectomy or radioactive iodine treatment (RAIT) in patients with differentiated thyroid cancer was associated with an increase in adverse pregnancy outcomes, such as miscarriage, preterm delivery, and congenital malformations. The results of this meta-analysis suggest that thyroid cancer treatment, including RAIT, is not associated with an increased risk of adverse pregnancy outcomes, including miscarriage, preterm labor, and congenital anomalies.

Abstract

This meta-analysis investigated whether thyroidectomy or radioactive iodine treatment (RAIT) in patients with differentiated thyroid cancer (DTC) was associated with an increase in adverse pregnancy outcomes, such as miscarriage, preterm delivery, and congenital malformations. A total of 22 articles (5 case-control and 17 case series studies) from 1262 studies identified through a literature search in the PubMed and EMBASE databases from inception up to 13 September 2021 were included. In patients with DTC who underwent thyroidectomy, the event rates for miscarriage, preterm labor, and congenital anomalies were 0.07 (95% confidence interval [CI], 0.05–0.11; 17 studies), 0.07 (95% CI, 0.05–0.09; 14 studies), and 0.03 (95% CI, 0.02–0.06; 17 studies), respectively. These results are similar to those previously reported in the general population. The risk of miscarriage or abortion was increased in patients with DTC when compared with controls without DTC (odds ratio [OR], 1.80; 95% CI, 1.28–2.53; I² = 33%; 3 studies), while the OR values for preterm labor and the presence of congenital anomalies were 1.22 (95% CI, 0.90–1.66; I² = 62%; five studies) and 0.73 (95% CI, 0.39–1.38; I² = 0%; two studies) respectively, which showed no statistical significance. A subgroup analysis of patients with DTC according to RAIT revealed that the risk of miscarriage, preterm labor, or congenital anomalies was not increased in the RAIT group when compared with patients without RAIT. The results of this meta-analysis suggest that thyroid cancer treatment, including RAIT, is not associated with an increased risk of adverse pregnancy outcomes, including miscarriage, preterm labor, and congenital anomalies.

Radiotherapy and pregnancy

We present the updated recommendations of the French society for radiation oncology on radiotherapy and pregnancy. The occurrence of cancer during pregnancy is a rare event (approximately 1 in 1000 pregnancies). The risks for the embryo or the foetus depend on the gestational age at the time of irradiation. The main risks are malformations with microcephaly and mental retardation. There is also a risk of radiation-induced cancer in the unborn child. In the case of only supradiaphragmatic irradiation, radiotherapy can be performed most often in pregnant women without risk to the foetus. On the other hand, in the case of an indication for subdiaphragmatic irradiation, therapeutic termination of the pregnancy should be proposed. In all cases, when radiotherapy is chosen, a phantom estimation of the dose delivered to the foetus, confirmed by in vivo measurement, is recommended. Conformational radiotherapy is the preferred technique because of the lower dose delivered to the foetus (except in tumour locations where other techniques such as IMRT are recommended).

Prenatal Radiation Exposure Leads to Higher-Order Telencephalic Dysfunctions in Adult Mice That Coincide with Reduced Synaptic Plasticity and Cerebral Hypersynchrony

Higher-order telencephalic circuitry has been suggested to be especially vulnerable to irradiation or other developmentally toxic impact. This report details the adult effects of prenatal irradiation at a sensitive time point on clinically relevant brain functions controlled by telencephalic regions, hippocampus (HPC), and prefrontal cortex (PFC). Pregnant C57Bl6/J mice were whole-body irradiated at embryonic day 11 (start of neurogenesis) with X-ray intensities of 0.0, 0.5, or 1.0 Gy. Female offspring completed a broad test battery of HPC-/PFC-controlled tasks that included cognitive performance, fear extinction, exploratory, and depression-like behaviors. We examined neural functions that are mechanistically related to these behavioral and cognitive changes, such as hippocampal field potentials and long-term potentiation, functional brain connectivity (by resting-state functional magnetic resonance imaging), and expression of HPC vesicular neurotransmitter transporters (by immunohistochemical quantification). Prenatally exposed mice displayed several higher-order dysfunctions, such as decreased nychthemeral activity, working memory defects, delayed extinction of threat-evoked response suppression as well as indications of perseverative behavior. Electrophysiological examination indicated impaired hippocampal synaptic plasticity. Prenatal irradiation also induced cerebral hypersynchrony and increased the number of glutamatergic HPC terminals. These changes in brain connectivity and plasticity could mechanistically underlie the irradiation-induced defects in higher telencephalic functions.

Radiation exposures in pregnancy, health effects and risks to the embryo/foetus-information to inform the medical management of the pregnant patient

Generally, intentional exposure of pregnant women is avoided as far as possible in both medical and occupational situations. This paper aims to summarise available information on sources of radiation exposure of the embryo/foetus primarily in medical settings. Accidental and unintended exposure is also considered. Knowledge on the effects of radiation exposure on the developing embryo/foetus remains incomplete-drawn largely from animal studies and two human cohorts but a summary is provided in relation to the key health endpoints of concern, severe foetal malformations/death, future cancer risk, and future impact on cognitive function. Both the specific education and training and also the literature regarding medical management of pregnant females is in general sparse, and consequently the justification and optimisation approaches may need to be considered on a case by case basis. In collating and reviewing this information, several suggestions for future basic science research, education and training, and radiation protection practice are identified.

Acute, Low-Dose Neutron Exposures Adversely Impact Central Nervous System Function

A recognized risk of long-duration space travel arises from the elevated exposure astronauts face from galactic cosmic radiation (GCR), which is composed of a diverse array of energetic particles. There is now abundant evidence that exposures to many different charged particle GCR components within acute time frames are sufficient to induce central nervous system deficits that span from the molecular to the whole animal behavioral scale. Enhanced spacecraft shielding can lessen exposures to charged particle GCR components, but may conversely elevate neutron radiation levels. We previously observed that space-relevant neutron radiation doses, chronically delivered at dose-rates expected during planned human exploratory missions, can disrupt hippocampal neuronal excitability, perturb network long-term potentiation and negatively impact cognitive behavior. We have now determined that acute exposures to similar low doses (18 cGy) of neutron radiation can also lead to suppressed hippocampal synaptic signaling, as well as decreased learning and memory performance in male mice. Our results demonstrate that similar nervous system hazards arise from neutron irradiation regardless of the exposure time course. While not always in an identical manner, neutron irradiation disrupts many of the same central nervous system elements as acute charged particle GCR exposures. The risks arising from neutron irradiation are therefore important to consider when determining the overall hazards astronauts will face from the space radiation environment.

Effects of Continuous In Utero Low- and Medium-Dose-Rate Gamma-Ray Exposure on Fetal Germ Cells

The effects of radiation exposure on germ cells and the gonads have been well studied at acute high-dose exposures, but the effects of chronic low-dose-rate (LDR) irradiation, particularly relevant for radiation protection, on germ cells and the gonads are largely unknown. Our previous study revealed that chronic exposure of mice to medium-dose-rate (MDR, 200 or 400 mGy/day) gamma-rays in utero for the entire gestation period (18 days) induced only a mild degree of general growth retardation, but with very drastic effects on the gonads and germ cells. In the current study, we further investigated the histomorphological changes in the gonads and the number of germ cells from gestation day (GD) 18 fetuses irradiated with MDR throughout the entire gestation period. The germ cells in the testes and ovaries of the MDR-irradiated fetuses were almost obliterated. Gestation day 18 fetuses exposed to LDR (20 mGy/day) radiation for the entire gestation period showed decreases in the number of the germ cells, which were not statistically significant or only marginally significant at most. Further investigations on the effects of LDR irradiation in utero using more sensitive methods are necessary.

Low- and moderate-dose non-cancer effects of ionizing radiation in directly exposed individuals, especially circulatory and ocular diseases: a review of the epidemiology

PURPOSE

There are well-known correlations between high and moderate doses (>0.5 Gy) of ionizing radiation exposure and circulatory system damage, also between radiation and posterior subcapsular cataract. At lower dose correlations with circulatory disease are emerging in the Japanese atomic bomb survivors and in some occupationally exposed groups, and are still to some extent controversial. Heterogeneity in excess relative risks per unit dose in epidemiological studies at low (<0.1 Gy) and at low-moderate (>0.1 Gy, <0.5 Gy) doses may result from confounding and other types of bias, and effect modification by established risk factors. There is also accumulating evidence of excess cataract risks at lower dose and low dose rate in various cohorts. Other ocular endpoints, specifically glaucoma and macular degeneration have been little studied. In this paper, we review recent epidemiological findings, and also discuss some of the underlying radiobiology of these conditions. We briefly review some other types of mainly neurological nonmalignant disease in relation to radiation exposure.

CONCLUSIONS

We document statistically significant excess risk of the major types of circulatory disease, specifically ischemic heart disease and stroke, in moderate- or low-dose exposed groups, with some not altogether consistent evidence suggesting dose-response non-linearity, particularly for stroke. However, the patterns of risk reported are not straightforward. We also document evidence of excess risks at lower doses/dose-rates of posterior subcapsular and cortical cataract in the Chernobyl liquidators, US Radiologic Technologists and Russian Mayak nuclear workers, with fundamentally linear dose-response. Nuclear cataracts are less radiogenic. For other ocular endpoints, specifically glaucoma and macular degeneration there is very little evidence of effects at low doses; radiation-associated glaucoma has been documented only for doses >5 Gy, and so has the characteristics of a tissue reaction. There is some evidence of neurological detriment following low-moderate dose (∼0.1-0.2 Gy) radiation exposure in utero or in early childhood.

Effects of fetal involvement of inadvertent radioactive iodine therapy for the treatment of thyroid diseases during an unsuspected pregnancy

Radioactive iodine (¹³¹I) therapy is absolutely contraindicated in pregnancy, but reports of inadvertent exposure continue to appear in the literature. Radiation-induced effects on the embryo/fetus are highly dependent on the stage of pregnancy, the dose absorbed by the embryo/fetus, and the manifestations of the pathological condition that develops as a result of the irradiation. Prior to implantation, the major concern is death of the embryo when exposed to radiation greater than the 100 mGy threshold. At this very early stage of pregnancy, exposure to ¹³¹I is unlikely to cause major malformations or thyroid dysfunction in surviving embryos. Exposure during organogenesis of the thyroid (from 10 weeks of gestation onward) and that of other organs at radiation thresholds of 100-300 mGy may result in fetal thyroid ablation, malformations, growth restriction, and in later life, mental retardation (MR). In addition, any dose of radiation exposure may increase the risk of cancer many years after the in utero exposure. Fetal and neonatal hypothyroidism due to in utero ¹³¹I exposure may require lifelong thyroxine replacement therapy and result in severe MR if the condition is not recognized immediately. Therefore, thyroid function must be evaluated and replacement therapy should be started without delay even before birth. Physicians treating women of childbearing age with ¹³¹I need to be aware of the risks of in utero ¹³¹I exposure and take all measures to avoid inadvertent exposure during pregnancy. Nevertheless, in case of accidental exposure, the clinician should confirm the gestational age at exposure, evaluate the risks to the fetus by estimating the radiation dose delivered, and discuss the subsequent management plan with the pregnant woman. This review aimed to summarize the current knowledge regarding the risk of harm to the developing fetus after in utero ¹³¹I exposure, especially focusing on the effects on thyroid function. This study also evaluated the most significant new findings regarding the prevention and in utero and peripartum management of fetal exposure to ¹³¹I.

Cognitive effects of low dose of ionizing radiation - Lessons learned and research gaps from epidemiological and biological studies

The last decades have seen increased concern about the possible effects of low to moderate doses of ionizing radiation (IR) exposure on cognitive function. An interdisciplinary group of experts (biologists, epidemiologists, dosimetrists and clinicians) in this field gathered together in the framework of the European MELODI workshop on non-cancer effects of IR to summarise the state of knowledge on the topic and elaborate research recommendations for future studies in this area. Overall, there is evidence of cognitive effects from low IR doses both from biology and epidemiology, though a better characterization of effects and understanding of mechanisms is needed. There is a need to better describe the specific cognitive function or diseases that may be affected by radiation exposure. Such cognitive deficit characterization should consider the human life span, as effects might differ with age at exposure and at outcome assessment. Measurements of biomarkers, including imaging, will likely help our understanding on the mechanism of cognitive-related radiation induced deficit. The identification of loci of individual genetic susceptibility and the study of gene expression may help identify individuals at higher risk. The mechanisms behind the radiation induced cognitive effects are not clear and are likely to involve several biological pathways and different cell types. Well conducted research in large epidemiological cohorts and experimental studies in appropriate animal models are needed to improve the understanding of radiation-induced cognitive effects. Results may then be translated into recommendations for clinical radiation oncology and imaging decision making processes.

Calculation of dose distribution in a realistic brain structure and the indication of space radiation influence on human brains

One of the most important steps in the near-future space age will be a crew mission returning to the Moon and even a manned mission to Mars. Unfortunately, such a mission will expose astronauts to unavoidable cosmic radiation in deep space and on the Martian or lunar surface. Thus, a better understanding of the radiation environment for such a mission and the consequent biological impacts on humans, in particular the human brains, is critical. The need for this better understanding is strongly suggested by investigations on animal models and on human patients who were undergoing irradiation for cancer therapy in the head. These have revealed unexpected alterations in the central nervous system behavior and sensitivity of mature neurons in the brain to charged particles. However, such experiments shall not be carried out realistically in space using humans. Therefore, to investigate the impact of cosmic radiation on human brains and the potential influence on the brain functions, we model and study the cosmic particle-induced radiation dose in a realistic head structure. Specifically speaking, 134 slices of computed tomography (CT) images of an actual human head have been used as a 3D phantom in Geant4 (GEometry ANd Tracking), which is a Monte Carlo tool for simulating energetic particles impinging into different parts of the brain and deliver radiation dose therein. As a first step, we compare the influence of different brain structures (e.g., with or without bones, with or without soft tissues) to the resulting dose therein to demonstrate the necessity of using a realistic brain structure for our investigation. Afterward, we calculate energy-dependent functions of dose distribution, for the most important (some of the most abundant and most biologically-relevant) particle types encountered during a deep space mission inside a spacecraft or habitat such as protons, helium ions, neutrons and some major heavier ions like carbon, nitrogen, and iron particles. Furthermore, two different scenarios have been modeled as a comparison: a human head without shielding protection and a human head with an aluminum shielding shell around (of varying thickness). These functions can then be used to fold with energetic cosmic-ray particle spectra of the ambient environment for obtaining the dose rate distribution at different lobes of the human brain. Our calculation of these functions can serve as a ready tool and a baseline for further evaluations of the radiation in the brain encountered during a space mission with different radiation fields, such as on the surface of the Moon or Mars.

Non-Human Primates Receiving High-Dose Total-Body Irradiation are at Risk of Developing Cerebrovascular Injury Years Postirradiation

Nuclear accidents and acts of terrorism have the potential to expose thousands of people to high-dose total-body iradiation (TBI). Those who survive the acute radiation syndrome are at risk of developing chronic, degenerative radiation-induced injuries [delayed effects of acute radiation (DEARE)] that may negatively affect quality of life. A growing body of literature suggests that the brain may be vulnerable to radiation injury at survivable doses, yet the long-term consequences of high-dose TBI on the adult brain are unclear. Herein we report the occurrence of lesions consistent with cerebrovascular injury, detected by susceptibility-weighted magnetic resonance imaging (MRI), in a cohort of non-human primate [(NHP); rhesus macaque, Macaca mulatta] long-term survivors of high-dose TBI (1.1-8.5 Gy). Animals were monitored longitudinally with brain MRI (approximately once every three years). Susceptibility-weighted images (SWI) were reviewed for hypointensities (cerebral microbleeds and/or focal necrosis). SWI hypointensities were noted in 13% of irradiated NHP; lesions were not observed in control animals. A prior history of exposure was correlated with an increased risk of developing a lesion detectable by MRI (P = 0.003). Twelve of 16 animals had at least one brain lesion present at the time of the first MRI evaluation; a subset of animals (n = 7) developed new lesions during the surveillance period (3.7-11.3 years postirradiation). Lesions occurred with a predilection for white matter and the gray-white matter junction. The majority of animals with lesions had one to three SWI hypointensities, but some animals had multifocal disease (n = 2). Histopathologic evaluation of deceased animals within the cohort (n = 3) revealed malformation of the cerebral vasculature and remodeling of the blood vessel walls. There was no association between comorbid diabetes mellitus or hypertension with SWI lesion status. These data suggest that long-term TBI survivors may be at risk of developing cerebrovascular injury years after irradiation.

Ionizing Radiation-Induced Epigenetic Modifications and Their Relevance to Radiation Protection

The present system of radiation protection assumes that exposure at low doses and/or low dose-rates leads to health risks linearly related to the dose. They are evaluated by a combination of epidemiological data and radiobiological models. The latter imply that radiation induces deleterious effects via genetic mutation caused by DNA damage with a linear dose-dependence. This picture is challenged by the observation of radiation-induced epigenetic effects (changes in gene expression without altering the DNA sequence) and of non-linear responses, such as non-targeted and adaptive responses, that in turn can be controlled by gene expression networks. Here, we review important aspects of the biological response to ionizing radiation in which epigenetic mechanisms are, or could be, involved, focusing on the possible implications to the low dose issue in radiation protection. We examine in particular radiation-induced cancer, non-cancer diseases and transgenerational (hereditary) effects. We conclude that more realistic models of radiation-induced cancer should include epigenetic contribution, particularly in the initiation and progression phases, while the impact on hereditary risk evaluation is expected to be low. Epigenetic effects are also relevant in the dispute about possible "beneficial" effects at low dose and/or low dose-rate exposures, including those given by the natural background radiation.

The psychological consequences of (perceived) ionizing radiation exposure: a review on its role in radiation-induced cognitive dysfunction

PURPOSE

Exposure to ionizing radiation following environmental contamination (e.g., the Chernobyl and Fukushima nuclear accidents), radiotherapy and diagnostics, occupational roles and space travel has been identified as a possible risk-factor for cognitive dysfunction. The deleterious effects of high doses (≥1.0 Gy) on cognitive functioning are fairly well-understood, while the consequences of low (≤0.1 Gy) and moderate doses (0.1-1.0 Gy) have been receiving more research interest over the past decade. In addition to any impact of actual exposure on cognitive functioning, the persistent psychological stress arising from perceived exposure, particularly following nuclear accidents, may itself impact cognitive functioning. In this review we offer a novel interdisciplinary stance on the cognitive impact of radiation exposure, considering psychological and epidemiological observations of different exposure scenarios such as atomic bombings, nuclear accidents, occupational and medical exposures while accounting for differences in dose, rate of exposure and exposure type. The purpose is to address the question that perceived radiation exposure - even where the actual absorbed dose is 0.0 Gy above background dose - can result in psychological stress, which could in turn lead to cognitive dysfunction. In addition, we highlight the interplay between the mechanisms of perceived exposure (i.e., stress) and actual exposure (i.e., radiation-induced cellular damage), in the generation of radiation-induced cognitive dysfunction. In all, we offer a comprehensive and objective review addressing the potential for cognitive defects in the context of low- and moderate-dose IR exposures.

CONCLUSIONS

Overall the evidence shows prenatal exposure to low and moderate doses to be detrimental to brain development and subsequent cognitive functioning, however the evidence for adolescent and adult low- and moderate-dose exposure remains uncertain. The persistent psychological stress following accidental exposure to low-doses in adulthood may pose a greater threat to our cognitive functioning. Indeed, the psychological implications for instructed cohorts (e.g., astronauts and radiotherapy patients) is less clear and warrants further investigation. Nonetheless, the psychosocial consequences of low- and moderate-dose exposure must be carefully considered when evaluating radiation effects on cognitive functioning, and to avoid unnecessary harm when planning public health response strategies.

NEUROENDOCRINE EFFECTS OF PRENATAL IRRADIATION FROM RADIOACTIVE IODINE (review)

BACKGROUND

Neuroendocrine effects of the prenatal radiation exposure from radioactive iodine in an event of nuclear power reactor accidents are a key issue in the field of radiation medicine and radiation safety because of a dramatic radiosensitivity of the developing organism.

OBJECTIVE

Review of contemporary epidemiological, clinical and experimental data on neuroendocrine effects of prenatal exposure to 131I.

OBJECT AND METHODS

Search in the PubMed/MEDLINE and Google Scholar abstract databases, along with a manual search for the relevant data sources.

RESULTS

Estimated absorbed doses of intrauterine thyroid irradiation from radioactive iodine were obtained based on ICRP Publication 88, both with estimates of effective radiation doses on embryo and fetus, and estimates of the brain equivalent doses upon exposure in utero. The latter ones are subject to updating. The evidence-based data has been presented regarding a radiation-associated reduction of head and chest circumference at birth, as well as a radiation-associated excess of goiter with large thyroid nodules, and possibly of thyroid cancer after a prenatal exposure to 131I radionuclides. Data on intrauterine brain damage are controversial, but most researchers share the view that there are cognitive and emotional-behavioral disorders due to prenatal and postnatal irradiation and psy- chosocial impacts. Incidence increase of non-cancerous endocrine disorders and degenerative vascular disease of retina was noted. An experimental model of intrauterine irradiation from 131I on Wistar rats was for the first time ever created, extrapolating the radioneuroembryological effects in rats to individuals prenatally exposed after the Chornobyl disaster. Late neuropsychiatric and endocrine effects may be resulted from the relatively short-term impact of ionizing radiation at a level previously been considered safe. The necessity of neuropsychiatric and endocrinological monitoring of individuals exposed prenatally to ionizing radiation after the Chornobyl catastrophe throughout their life is substantiated. Experimental animal studies are a key direction in the further research of radiation effects, especially associated with low radiation doses. Further experimental and clinical neuroradiobio- logical studies aimed at exploration of the effect of ionizing radiation on hippocampal neurogenesis are most rele- vant nowadays.

Challenges to the central nervous system during human spaceflight missions to Mars

Space travel presents a number of environmental challenges to the central nervous system, including changes in gravitational acceleration that alter the terrestrial synergies between perception and action, galactic cosmic radiation that can damage sensitive neurons and structures, and multiple factors (isolation, confinement, altered atmosphere, and mission parameters, including distance from Earth) that can affect cognition and behavior. Travelers to Mars will be exposed to these environmental challenges for up to 3 years, and space-faring nations continue to direct vigorous research investments to help elucidate and mitigate the consequences of these long-duration exposures. This article reviews the findings of more than 50 years of space-related neuroscience research on humans and animals exposed to spaceflight or analogs of spaceflight environments, and projects the implications and the forward work necessary to ensure successful Mars missions. It also reviews fundamental neurophysiology responses that will help us understand and maintain human health and performance on Earth.

Novel in vitro assay to investigate radiation induced changes in the functionality of human embryonic stem cell-derived neurospheres

Ionizing radiation (IR) is increasingly used for diagnostics and therapy of severe brain diseases. However, IR also has adverse effects on the healthy brain tissue, particularly on the neuronal network. This is true for adults but even more pronounced in the developing brain of unborn and pediatric patients. Epidemiological studies on children receiving radiotherapy showed an increased risk for cognitive decline ranging from mild deficits in academic functioning to severe late effects in intellectual ability and language as a consequence of altered neuronal development and connectivity. To provide a comprehensive approach for the analysis of radiation-induced alterations in human neuronal functionality, we developed an in vitro assay by combining microelectrode array (MEA) analyses and human embryonic stem cell (hESC) derived three-dimensional neurospheres (NS). In our proof of principle study, we irradiated hESC with 1 Gy X-rays and let them spontaneously differentiate into neurons within NS. After the onset of neuronal activity, we recorded and analyzed the activity pattern of the developing neuronal networks. The network activity in NS derived from irradiated hESC was significantly reduced, whereas no differences in molecular endpoints such as cell proliferation and transcript or protein expression analyses were found. Thus, the combination of MEA analysis with a 3D model for neuronal functionality revealed radiation sequela that otherwise would not have been detected. We therefore strongly suggest combining traditional biomolecular methods with the new functional assay presented in this work to improve the risk assessment for IR-induced effects on the developing brain.

Abnormal retinal pigment epithelium melanogenesis as a major determinant for radiation-induced congenital eye defects

Recent studies highlighted a link between ionizing radiation exposure during neurulation and birth defects such as microphthalmos and anophthalmos. Because the mechanisms underlying these defects remain largely unexplored, we irradiated pregnant C57BL/6J mice (1.0 Gy, X-rays) at embryonic day (E)7.5, followed by histological and gene/protein expression analyses at defined days. Irradiation impaired embryonic development at E9 and we observed a delayed pigmentation of the retinal pigment epithelium (RPE) at E11. In addition, a reduced RNA expression and protein abundance of critical eye-development genes (e.g. Pax6 and Lhx2) was observed. Furthermore, a decreased expression of Mitf, Tyr and Tyrp1 supported the radiation-induced perturbation in RPE pigmentation. Finally, via immunostainings for proliferation (Ki67) and mitosis (phosphorylated histone 3), a decreased mitotic index was observed in the E18 retina after exposure at E7.5. Overall, we propose a plausible etiological model for radiation-induced eye-size defects, with RPE melanogenesis as a major determining factor.

Breast Cancer during Pregnancy-Current Paradigms, Paths to Explore

Breast cancer is the most common form of malignancy in pregnant women. The prevalence of pregnancy-associated breast cancer (PABC) is up to 0.04% of pregnancies and is expected to rise in developed countries. PABC represents a unique clinical scenario which requires a delicate balance of risks and benefits for both maternal and fetal well-being. Currently, there is paucity of data regarding the short- and long-term outcomes of in-utero exposure to anti-neoplastic agents. In general, when possible, treatment for PABC should follow the same guidelines as in non-pregnant patients. Surgery, including sentinel lymph node biopsy, is possible during all trimesters of pregnancy. Radiotherapy is contraindicated during pregnancy, although it might be considered in highly selected patients based on risk-benefit assessment. Evidence supports that administration of chemotherapy may be safe during the second and third trimesters, with cessation of treatment three weeks prior to expected delivery. Currently, hormonal therapy and anti-HER2 agents are contraindicated during pregnancy and should be postponed until after delivery. Prematurity is associated with worse neonatal and long-term outcomes, and thus should be avoided. While current data on the long-term effects of anti-neoplastic treatments are reassuring, grade of evidence is lacking, hence additional large prospective studies with long-term follow-up are essential to rule out any treatment-induced adverse effects.

Internal exposure risk due to radiocesium and the consuming behaviour of local foodstuffs among pregnant women in Minamisoma City near the Fukushima nuclear power plant: a retrospective observational study

OBJECTIVES

This study aimed to evaluate the internal cesium (Cs) level among pregnant women in Minamisoma City (the area straddling the evacuation zones) over a 5-year period after Japan's 2011 Fukushima nuclear accident and assess the status and transition of their food-acquiring preferences during this period.

DESIGN

A retrospective observational study of a screening along with a questionnaire survey.

SETTING

This study was conducted in an obstetrics and gynaecology service in Minamisoma City in Fukushima, Japan.

PARTICIPANTS

Participants included pregnant women who applied for the voluntary internal radiation exposure screening programme.

PRIMARY AND SECONDARY OUTCOME MEASURES

Internal radiation exposure was evaluated using the whole-body counter (WBC) in the screening programme. Data from a food acquisition preference questionnaire administered to the participants were analysed and compared across the 5-year period after adjusting for covariates.

RESULTS

Overall, 804 screening programmes were conducted with 579 participants during the study period. All participants had internal contamination levels below the detection limit of the WBC unit (220 and 250 Bq/body for Cs-134 and Cs-137, respectively). Based on the most conservative assumption, their maximum annual effective doses by Cs-134 and Cs-137 together were estimated at 16 µSv/year. Contrary to limited internal contamination risks and counter-dose initiatives by the government, a considerable number of pregnant women were still concerned about consuming potentially contaminated local food products when purchasing them at supermarkets between 2012 (78.4%) and 2015 (75.0%).

CONCLUSIONS

Health effects from post-accident internal radiation exposure were likely to be insignificant in pregnant women. National/local action is urgently needed to promote scientific understanding in pregnant women regarding limited internal exposure risks from local food products in the market. However, few mothers chose to participate in the internal radiation exposure screening programme, and thus, caution is required in interpreting the results of analyses.

Epidemiological studies of atomic bomb radiation at the Radiation Effects Research Foundation

Epidemiological studies of people who were exposed to atomic bomb radiation and their children who were conceived after parental exposure to radiation (F₁) have investigated late health effects of atomic bomb radiation and its transgenerational effects. Those studies were initiated by the Atomic Bomb Casualty Commission (ABCC) in the 1950s. ABCC was reorganized to the Radiation Effects Research Foundation (RERF) in 1975, which continued the work of the ABCC. Follow-up of vital status and cause of death is performed for all RERF cohorts, including the atomic bomb survivors (the Life Span Study: LSS), in utero survivors, and the children of the survivors (F₁). Cancer incidence is investigated for accessible subpopulations of the cohorts. Health examinations for subcohorts of the LSS and in utero survivors are conducted as the Adult Health Study (AHS); a program of health examinations for a subcohort of the F₁ study is called the F₁ Offspring Clinical Study (FOCS). Participants of all clinical programs are asked to donate their blood and urine for storage and future biomedical investigations. Epidemiological studies have observed increased radiation risks for malignant diseases among survivors including those exposed in utero, and possible risks for some noncancer diseases. No increased risks due to parental exposure to radiation have been observed for malignancies or other diseases in F₁, but continuing investigations are required.

Prenatal Irradiation-Induced Hippocampal Abnormalities in Rats Evaluated Using Manganese-Enhanced MRI

The aim of this study was to characterize hippocampal abnormalities in rats after prenatal x-ray irradiation using manganese-enhanced MRI (MEMRI). All radiation-exposed rat brains showed a reduced volume with prominent dilatation of lateral ventricles. Moreover, MEMRI-enhanced areas within the hippocampus were reduced in volumes by approximately 25% of controls, although the entire volume of hippocampus was decreased by approximately 50% of controls. MEMRI signals were enhanced strongly in the hilus and granular layer of the dentate gyrus (DG) and the pyramidal layer and infrapyramidal region of the CA3 region, and moderately along the CA1/2 pyramidal cell layer in the control rats. In radiation-exposed rats, MEMRI signals in the CA1/2 regions disappeared due to disrupting their laminar organization, although strong MEMRI signals were sustained in the DG and CA3 regions. Histopathological examinations in radiation-exposed rats revealed disorganizations of the DG granule cell layer and the CA3 pyramidal cell layer with reducing the cell density. The CA1/2 pyramidal cell layer was disrupted by invading ectopic cell mass. Neural cell adhesion molecule (NCAM)-positive fiber bundles were sustained in radiation-exposed rats, although they distributed aberrantly in the suprapyramidal CA3 region with a slight reduction of NCAM staining. Furthermore, glial components consisted largely by astrocytes and minor by microglia were densely distributed in the DG rather than in other hippocampal regions, and their density radiation-exposed rats. In conclusion, MEMRI signal enhancements could delineate different neuronal and/or glial components among hippocampal regions. We characterized microstructures of the deformed hippocampus as well as its macrostructures in a prenatally radiation-exposed rat model using in vivo MEMRI. The present findings provide advantageous information for detecting nondestructively hippocampal deformations in neurodevelopmental disorders.

Low dose or low dose rate ionizing radiation-induced health effect in the human

The extensive literature review on human epidemiological studies suggests that low dose ionizing radiation (LDIR) (≤100 mSv) or low dose rate ionizing radiation (LDRIR) (<6mSv/H) exposure could induce either negative or positive health effects. These changes may depend on genetic background, age (prenatal day for embryo), sex, nature of radiation exposure, i.e., acute or chronic irradiation, radiation sources (such as atomic bomb attack, fallout from nuclear weapon test, nuclear power plant accidents, ⁶⁰Co-contaminated building, space radiation, high background radiation, medical examinations or procedures) and radionuclide components and human epidemiological experimental designs. Epidemiological and clinical studies show that LDIR or LDRIR exposure may induce cancer, congenital abnormalities, cardiovascular and cerebrovascular diseases, cognitive and other neuropsychiatric disorders, cataracts and other eye and somatic pathology (endocrine, bronchopulmonary, digestive, etc). LDIR or LDRIR exposure may also reduce mutation and cancer mortality rates. So far, the mechanisms of LDIR- or LDRIR -induced health effect are poorly understood. Further extensive studies are still needed to clarify under what circumstances, LDIR or LDRIR exposure may induce positive or negative effects, which may facilitate development of new therapeutic approaches to prevent or treat the radiation-induced human diseases or enhance radiation-induced positive health effect.

Radioprotective effect of epimedium on neurogenesis and cognition after acute radiation exposure

The radioprotective effect of herb epimedium (or yin yang huo) extract (5 g/kg, oral administration daily for 4 weeks) on neurogenesis and cognition after acute radiation exposure with 5.5 Gy was evaluated in Balb/c mice by behavioral tests and immunohistochemical study. The results indicated that epimedium extract could improve animal weight loss, locomotor activity and spatial learning and memory which are similar to pre-irradiation intraperitoneal injection (100 mg/kg) of amifostine phosphate, a well- known radioprotective drug. Immunohistochemical study showed that epimedium extract prevented the loss of proliferation cells, newly generated neurons, and interneurons in the hilus, in particular, the subgranular zone of the dentate gyrus. It suggests that herb epimedium may be a promising radio-neuro-protective drug to prevent radiation-induced neuropsychological disorders.

Radical change of apoptotic strategy following irradiation during later period of embryogenesis in medaka (Oryzias latipes)

Induction of apoptosis in response to various genotoxic stresses could block transmission of teratogenic mutations to progeny cells. The severity of biological effects following irradiation depends on the stage at which embryos are irradiated during embryogenesis. We reported previously that irradiation of medaka embryos 3 days post fertilization (dpf) with 10 Gy of gamma rays induced high incidence of apoptotic cells in the mid-brain, however, the embryos hatched normally and developed without apparent malformations. To determine the severity of biological effects following irradiation during a later period of embryogenesis, embryos of various developmental stages were irradiated with 15 Gy of gamma rays and examined for apoptotic induction at 24 h after irradiation in the brain, eyes and pharyngeal epithelium tissues, which are actively proliferating and sensitive to irradiation. Embryos irradiated at 3 dpf exhibited many apoptotic cells in these tissues, and all of them died due to severe malformations. In contrast, embryos irradiated at 5 dpf showed no apoptotic cells and subsequently hatched without apparent malformations. Embryos irradiated at 4 dpf had relatively low numbers of apoptotic cells compared to those irradiated at 3 dpf, thereafter most of them died within 1 week of hatching. In adult medaka, apoptotic cells were not found in these tissues following irradiation, suggesting that apoptosis occurs during a restricted time period of medaka embryogenesis throughout the life. No apoptotic cells were found in irradiated intestinal tissue, which is known to be susceptible to radiation damage in mammals, whereas many apoptotic cells were found in proliferating spermatogonial cells in the mature testis following irradiation. Taken together, with the exception of testicular tissue, the results suggest a limited period during medaka embryogenesis in which irradiation-induced apoptosis can occur.

Intratumoral evaluation of 3D microvasculature and nanoparticle distribution using a gadolinium-dendron modified nano-liposomal contrast agent with magnetic resonance micro-imaging

The enhanced permeability and retention (EPR) effect is variable depending on nanoparticle properties and tumor/vessel conditions. Thus, intratumoral evaluations of the vasculature and nanoparticle distribution are important for predicting the therapeutic efficacy and the intractability of tumors. We aimed to develop a tumor vasculature evaluation method and high-resolution nanoparticle delivery imaging using magnetic resonance (MR) micro-imaging technology with a gadolinium (Gd)-dendron assembled liposomal contrast agent. Using the Gd-liposome and a cryogenic receiving coil, we achieved 50-μm isotropic MR angiography with clear visualization of tumor micro-vessel structure. The Gd-liposome-enhanced MR micro-imaging revealed differences in the vascular structures between Colon26- and SU-DHL6-grafted mice models. The vessel volumes and diameters measured for both tumors were significantly correlated with histological observations. The MR micro-imaging methods facilitate the evaluation of intratumoral vascularization patterns, the quantitative assessment of vascular-properties that alter tumor malignancy, particle retentivity, and the effects of treatment.

When a duck is not a duck; a new interdisciplinary synthesis for environmental radiation protection

This consensus paper presents the results of a workshop held in Essen, Germany in September 2017, called to examine critically the current approach to radiological environmental protection. The meeting brought together participants from the field of low dose radiobiology and those working in radioecology. Both groups have a common aim of identifying radiation exposures and protecting populations and individuals from harmful effects of ionising radiation exposure, but rarely work closely together. A key question in radiobiology is to understand mechanisms triggered by low doses or dose rates, leading to adverse outcomes of individuals while in radioecology a key objective is to recognise when harm is occurring at the level of the ecosystem. The discussion provided a total of six strategic recommendations which would help to address these questions.

Effects of Continuous Gamma-Ray Exposure In Utero in B6C3F1 Mice on Gestation Day 18 and at 10 Weeks of Age

Pregnant C57BL/6JJcl mice were exposed to γ rays at low dose rate (20 mGy/day, LDR) or medium dose rate (200 and 400 mGy/day, MDR) from gestation day (GD) 0-18 to total accumulated doses of 360, 3,600 and 7,200 mGy, respectively. An additional group of pregnant mice were acutely exposed to 2 Gy at high dose rate (HDR) of 0.77 Gy/min on GD 11. In experiment 1, fetuses collected via cesarean section on GD 18 were examined for external and skeletal abnormalities. While the results of LDR exposure (20 mGy/day) did not significantly differ from the nonirradiated controls in all parameters examined, MDR (200 and 400 mGy/day) and acute HDR (2 Gy) exposure caused growth retardation and significantly increased incidence of unossified bones. Increased incidence of external abnormalities was observed only in the acute HDR group. In experiment 2, the dams were allowed to give birth and the pups were clinically monitored and weighed periodically until 10 weeks of age when they were sacrificed and subjected to pathological examination. Pups exposed at MDRs of 200 and 400 mGy/dayand at acute HDR of 0.77 Gy/min had lower bodyweights from weaning (3 weeks) to 10 weeks of age except for females exposed to 400 mGy/day MDR. None of the pups exposed to an acute 2 Gy dose on GD 11 survived to 10 weeks of age. Histopathological changes were not significantly different between the nonirradiated control and the 20 mGy/day LDR groups. However, at both MDR exposures of 200 and 400 mGy/day. gonadal (testes and ovary) hypoplasia/atrophy was observed in all the 10-week-old pups. Our results show that in utero LDR exposure to 20 mGy/day for the entire gestation period did not cause any significant effect in pups when compared to the nonirradiated controls up to 10 weeks of age. However, pups exposed in utero to MDRs showed dose-related growth retardation with delayed ossifications (400 mGy/day) and gonadal hypoplasia/atrophy. These findings suggest that increased post-implantation loss in dams exposed at MDR is due to early embryonic deaths resulting in early resorption.

Neonatal outcomes following exposure in utero to fallout from Chernobyl

Iodine 131 (I-131), the principal component of nuclear fallout from the Chernobyl accident, concentrates in the thyroid gland and may pose risks to fetal development. To evaluate this, neonatal outcomes following the accident in April of 1986 were investigated in a cohort of 2582 in utero-exposed individuals from northern Ukraine for whom estimates of fetal thyroid I-131 dose were available. We carried out a retrospective review of cohort members' prenatal, delivery and newborn records. The relationships of dose with neonatal anthropometrics and gestational length were modeled via linear regression with adjustment for potentially confounding variables. We found similar, statistically significant dose-dependent reductions in both head circumference (-1.0 cm/Gy, P = 0.005) and chest circumference (-0.9 cm/Gy, P = 0.023), as well as a similar but non-significant reduction in neonatal length (-0.6 cm/Gy, P = 0.169). Gestational length was significantly increased with increasing fetal dose (0.5 wks/Gy, P = 0.007). There was no significant (P > 0.1) effect of fetal dose on birth weight. The observed associations of radioiodine exposure with decreased head and chest circumference are consistent with those observed in the Japanese in utero-exposed atomic bomb survivors.

A detailed characterization of congenital defects and mortality following moderate X-ray doses during neurulation

BACKGROUND

Both epidemiological and animal studies have previously indicated a link between in utero radiation exposure and birth defects such as microphthalmos, anophthalmos, and exencephaly. However, detailed knowledge on embryonic radiosensitivity during different stages of neurulation is limited, especially in terms of neural tube defect and eye defect development.

METHODS

To assess the most radiosensitive stage during neurulation, pregnant C57BL6/J mice were X-irradiated (0.5 Gy or 1.0 Gy) at embryonic days (E)7, E7.5, E8, E8.5, or E9. Next, the fetuses were scored macroscopically for various defects and prenatal resorptions/deaths were counted. In addition, cranial skeletal development was ascertained using the alcian-alizarin method. Furthermore, postnatal/young adult survival was followed until 5 weeks (W5) of age, after X-irradiation at E7.5 (0.1 Gy, 0.5 Gy, or 1.0 Gy). In addition, body and brain weights were registered at adult age (W10) following X-ray exposure at E7.5 (0.1 Gy, 0.5 Gy).

RESULTS

Several malformations, including microphthalmos and exencephaly, were most evident after irradiation at E7.5, with significance starting respectively at 0.5 Gy and 1.0 Gy. Prenatal mortality and weight were significantly affected in all irradiated groups. Long-term follow-up of E7.5 irradiated animals revealed a reduction in survival at 5 weeks of age after high dose exposure (1.0 Gy), while lower doses (0.5 Gy, 0.1 Gy) did not affect brain and body weight at postnatal week 10.

CONCLUSIONS

With this study, we gained more insight in radiosensitivity throughout neurulation, and offered a better defined model to further study radiation-induced malformations and the underlying mechanisms.

Gilbert W. Beebe Symposium on 30 Years after the Chernobyl Accident: Current and Future Studies on Radiation Health Effects

This commentary summarizes the presentations and discussions from the 2016 Gilbert W. Beebe symposium "30 years after the Chernobyl accident: Current and future studies on radiation health effects." The symposium was hosted by the National Academies of Sciences, Engineering, and Medicine (the National Academies). The symposium focused on the health consequences of the Chernobyl accident, looking retrospectively at what has been learned and prospectively at potential future discoveries using emerging 21st Century research methodologies.