Epidemiology is the study of the distribution and determinants of diseases or other healthrelated events. Descriptive epidemiology aims to investigate the distribution of diseases by time, region or in different groups of individuals, while analytical studies are used to study determinants of diseases. The most common analytical approaches are case-control studies and cohort studies. Both study designs are introduced with respect to methods, measures of risk, weaknesses and strengths. Examples for radiation epidemiological studies are the atomic bomb survivors of Hiroshima and Nagasaki, and occupationally, environmentally or medically radiation exposed populations. Generally, the choice of the study design depends on many factors such as the disease (frequency, latency) and the exposure (rare or not) to be studied, the time over which the study can be carried out, the resources available to collect detailed individual data and the potential to minimize bias and confounding. The interpretation of results of epidemiological studies requires consideration of systematic errors (information bias, selection bias), confounding and chance. Finally, the likelihood that an association between radiation exposure and health outcome is causal should be evaluated. Criteria for assessing if an association is causal include temporal relationship, biological plausibility, consistency, strength of the association, exposure-response relationship, reversibility and coherence.

This article focuses on issues and associated challenges in radiation risk communication to the public. All of the issues start with very simple questions and the challenges are to answer them in a way that can be easily understood by the public. Two of the most commonly asked questions are addressed, “what is radiation?” and “are we safe?”. The discussion is based mostly on information available on the internet to the public. Collectively, more is known and understood about the biological effects of radiation than any other toxin or carcinogen. As health physicists, we are confident that current radiation dose limits protect workers and the public. It is our duty to engage the public, address their concerns, translate our knowledge to their language, and eventually build trust among us. From the discussion given here, one can see that radiation risk communication to the public is a science-based art. Depending on how it is designed, the communication can be a beauty to people when it makes their life easier, or it can turn into a beast when it makes people even more scared of radiation.

In case of a radiological emergency, it is essential to assess the possible dose received by possible victims. Several disciplines, such as physical dosimetry, dose reconstruction and biological dosimetry should put together their expertise to respond as fast as possible. Among different methods used in biological dosimetry, “dicentric analysis” is still the most widely used method, as it has the lowest detection limit, is the one that most accurately estimates the dose, and distinguishes between whole- and partial-body irradiations. To score dicentric chromosomes, peripheral blood lymphocytes have to be stimulated to enter the cell cycle and reach metaphase. In addition, skilled scorers should analyze at the microscope complete cells containing 46 centromeres and to recognize dicentrics chromosomes with their corresponding acentric fragment. For this reason, dicentric analysis is time consuming and in case of an accident involving a large number of victims, it should not be possible to respond promptly. One promising improvement of the methodology is to automate dicentric analysis, and nowadays several laboratories of biological dosimetry have the equipment needed to perform automatic dicentric scoring (ADS). Here we present a review of different experiences carried out at the “Institut de Radioprotection et Surete Nucleaire” from France to compare ADS in relation to manual scoring (MS) and evaluate the feasibility to introduce ADS as a real option to be used instead of MS. The experience obtained indicates that automatic dicentric scoring is a real alternative and is mature enough to substitute manual scoring.

Rapid test of radioactivity contamination in foods/foodstuffs is required to ensure the radiological protection of the public in emergency situation. Just after the Fukushima accident rapid screening of radio-iodine radioactivity in foods/foodstuffs was carried out through over the country. In the present paper, the rapid test method based on the Ministry of Health, Labour and Welfare manual for radioactivity measurements in emergency, which were specified as the normative references for radioactivity monitoring of foods/foodstuffs by testing laboratories, is shown with some considerations for the expected future improvement.

General survey for the environmental radon and thoron has been performed in Minamidaitojima, Okinawa prefecture, southwestern part of Japan. In situ measurements of the radon and thoron exhalation rates were conducted at a total of 7 points using an accumulation technique with a ZnS(Ag) scintillation detector. The medians of radon and thoron exhalation rates were estimated to be 31 mBq m-2 s-1 and 3,970 mBq m-2 s-1, respectively. The atmospheric radon concentrations were measured at 2 points with an ionization chamber, and the maximum concentration was estimated to be 94 Bq m-3. For the surface soil samples collected at the measurement points of the exhalation rates, arithmetic means for 238U and 232Th series concentration were estimated to be approximately 145 Bq kg-1 dry and 101 Bq kg-1 dry, respectively. These results indicated that the environmental radon and thoron levels in Minamidaito-jima are fairly higher than those of the average of Japan. And it is strongly suggested that the exhalation rates and the concentrations are enhanced mainly due to the surface soil with the relatively high radioactivity.

Interventional radiology (IVR) procedures are indispensable in treatment directly connected to lifesaving. As IVR requires X-ray irradiation for a long time and is carried out repeatedly, the skin dose to the patient is high. We measured waveforms of the entrance surface dose in pulsed fluoroscopy with the intent of reducing the exposure dose from IVR. Using a flat-panel detector (FPD) system, we also measured entrance surface doses in various cases in normaland low-dose modes. As a result, wavetail cutoff of waveforms was confirmed. In addition, we confirmed that in each of the cases of lower pulse rates, lower frame rates, larger FPD sizes, larger irradiation fields, shorter table-FPD distances, and thinner phantom thicknesses,doses decreased. Based on these results, from the perspective of reducing exposure doses, fluoroscopy or exposure should be undertaken using: a low pulse rate; a low frame rate during exposure; a large FPD size without magnification; an irradiation field that is not small; and an FPD brought to close to the patient.

Ionizing radiation is a potent genotoxic agent that can induce delayed biological effects referred to as genomic instability. Delayed chromosomal instability has been studied as a typical phenotype of genomic instability in the progeny of irradiated cells, but the mechanisms by which it arises remain obscure. The previous chromosome transfer study revealed that chromosomal instability could be transmitted to the progeny of unirradiated recipient cells by a chromosome exposed to ionizing radiation1). To determine whether the transmitted chromosomal instability is promoted in cells with compromised genomic integrity, we examined chromosome transfer to the cells which have defect of DNA repair genes, such as ataxia telangiectasia mutated gene (ATM), Nijmegen breakage syndrome protein 1 gene (NBS1) and Werner syndrome (WRN) gene. Unfortunately, we could not get clone of ATM or NBS1 deficient cells but we could get Werner syndrome cell line (WS780: WRNmut) which carries transferred chromosome 9. The results indicated that both unirradiated and irradiated chromosomes 9 were stable after chromosome transfer in microcell hybrids derived from non-WS control cells (GM638: WRNwt). In contrast, although all six WRNmutderived microcell hybrids had no rearrangements in the transferred-unirradiated chromosome 9, 11-28% of cells showed the rearranged chromosome 9 in three out of seven WRNmut-derived microcell hybrids transferred with the 6 Gy-irradiated chromosome 9. Thus, the present study demonstrates the possibility that chromosome instability mediated by an irradiated chromosome is promoted in WS cells that harbor multiple defects of genomic integrity.

Radioactive materials are produced when a linear accelerator (LINAC) generating highenergy X rays is operated. The following two methods are followed for disposing of these materials in Japan: 1) consigning disposal of the materials to the Radioisotope Association or 2) using a radioactive contaminant confirmation system that allows very-low-dose radioactive contaminants to be disposed of as industrial waste. Identification of radioactive nuclides is required for both methods, and nuclide identification using a high-purity germanium (HPGe) detector is indispensable under the existing circumstances. Upon the disposal of a LINAC in this study, we conducted nuclide analyses using both an HPGe detector and an NaI(Tl) detector, and compared the results. Eleven nuclides were detected in the analysis using the HPGe detector. ⁵¹Cr, ⁵⁴Mn and/or ⁵⁸Co, ⁶⁰Co, ⁶⁵Zn, ¹²⁴Sb and ¹⁹⁸Au could be detected using the NaI(Tl) detector, while ⁵⁷Co, ^110mAg, ¹⁸¹W and ¹⁹⁶Au could not be identified with this detector. However, if the count of a spectrum is large and the energy distribution waveforms bore no　similarity, nuclides could be identified. The study suggests that an NaI(Tl) detector could be　also used for measurement of radioactive materials.

Monte Carlo calculations were carried out to evaluate absorbed dose rates in air and dose buildup factors at a height of 1 m above the air-ground interface for underground ¹³⁴Cs and ¹³⁷Cs sources having three typical types of depth profile, i.e. slab, exponential and triangular sources. The calculated results showed that the respective dose rates and buildup factors were relatively different one another. In addition, a linear relationship was found between mean source depths expressed in natural logarithm and the corresponding dose rates.

We have collected surface soil samples on the campus of Nihon University, Koriyama, Fukushima, Japan, after the Fukushima Dai-ichi Nuclear Power Plant accident for three years and measured their radiocesium (¹³⁴Cs and ¹³⁷Cs) concentrations to understand the behavior of deposited radiocesium on soil surfaces in the campus. In 2011, the inventory of ¹³⁴Cs and ¹³⁷Cs ranged from 73 to 164 kBq m-2 with the arithmetic mean value of 110 ± 33 kBq m-2, and from 83 to 203 kBq m-2 with the arithmetic mean value of 134 ± 42 kBq m-2, respectively. In 2012 and 2013, we found radiocesium inventories were rapidly decreasing at most sampling stations because of university decontamination work programs to remove the surface soil to a depth of 5 cm. Slightly increasing radiocesium inventories were observed at some stations, however, where soil and grass covered soil areas met. We considered that the elevated radiocesium inventories were affected by resuspension of soil dust. The ¹³⁷Cs residual rate at areas that had not been decontaminated was estimated at approximately 50% during 2012 to 2013.