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An enormous amount of environmental monitoring data has been acquired by various organisations for the evaluation and implementation of countermeasures to mitigate the effects of the accident at the Fukushima Daiichi Nuclear Power Plant. However, it is difficult to collate, compare, and analyse this data because it was published in different formats at different sites according to the respective objectives of the publishing organisations. Moreover, these organisations have been accumulating data in large volumes for over nine years after the accident. We established procedures to collect this data, convert them into a unified format, classify them according to categories, and make the data accessible on a web-based database system. The database contains environmental monitoring data on air dose rates, ground deposition densities, and concentrations in various environmental samples such as soil, water, and food. This data is being provided not only in numerical format for quantitative analysis but also as distribution maps and time-series graphs for visual understanding. The database system enabled us to spatially and temporally compare large volumes of monitoring data. By using the database functions, characteristics of some representative data in the database was clarified. [ABSTRACT FROM AUTHOR]

A large-scale environmental monitoring effort, construction of detailed contamination maps based on the monitoring data, studies on radiocaesium migration in natural environments, construction of a prediction model for the air dose rate distribution in the 80 km zone, and construction of a database to preserve and keep open the obtained data have been implemented as national projects. Temporal changes in contamination conditions were analysed. It was found that air dose rates above roads have decreased much faster than those above undisturbed flat fields. Further, the decreasing tendency was found to depend on land uses, magnitudes of initial dose rates and some other factors. [ABSTRACT FROM AUTHOR]

Preliminary prediction models have been studied for the radioactive caesium distribution within the 80-km radius of the Fukushima Daiichi nuclear power plant. The models were represented by exponential functions using ecological half-life of radioactive caesium in the environment. The ecological half-lives were derived from the changes in ambient dose equivalent rates through vehicle-borne surveys. It was found that the ecological half-lives of radioactive caesium were not constant within the 80-km radius of the Fukushima Daiichi nuclear power plant. The ecological half-life of radioactive caesium in forest areas was found to be much larger than that in urban and water areas. [ABSTRACT FROM AUTHOR]

Background: Clonogenicity gives important information about the cellular reproductive potential following ionizing irradiation, but an abortive colony that fails to continue to grow remains poorly characterized. It was recently reported that the fraction of abortive colonies increases with increasing dose. Thus, we set out to investigate the production kinetics of abortive colonies using a model of branching processes. Methodology/Principal Findings: We firstly plotted the experimentally determined colony size distribution of abortive colonies in irradiated normal human fibroblasts, and found the linear relationship on the log-linear or log-log plot. By applying the simple model of branching processes to the linear relationship, we found the persistent reproductive cell death (RCD) over several generations following irradiation. To verify the estimated probability of RCD, abortive colony size distribution (≤15 cells) and the surviving fraction were simulated by the Monte Carlo computational approach for colony expansion. Parameters estimated from the log-log fit demonstrated the good performance in both simulations than those from the log-linear fit. Radiation-induced RCD, i.e. excess probability, lasted over 16 generations and mainly consisted of two components in the early (<3 generations) and late phases. Intriguingly, the survival curve was sensitive to the excess probability over 5 generations, whereas abortive colony size distribution was robust against it. These results suggest that, whereas short-term RCD is critical to the abortive colony size distribution, long-lasting RCD is important for the dose response of the surviving fraction. Conclusions/Significance: Our present model provides a single framework for understanding the behavior of primary cell colonies in culture following irradiation. [ABSTRACT FROM AUTHOR]

In order to provide fundamental data required for dose evaluation due to environmental exposures, effective dose conversion coefficients, that is, the effective dose rate per unit activity per unit area, were calculated for a number of potentially important radionuclides, assuming an exponential distribution in ground, over a wide range of relaxation depths. The conversion coefficients were calculated for adults and a new-born baby on the basis of dosimetric methods that the authors and related researchers have previously developed, using Monte Carlo simulations and anthropomorphic computational phantoms. The differences in effective dose conversion coefficients due to body size between the adult and baby phantoms were found to lie within 50 %, for most cases; however, for some low energies, differences could amount to a factor of 3. The effective dose per unit source intensity per area was found to decrease by a factor of 2-5, for increasing relaxation depths from 0 to 5 g/cm, above a source energy of 50 keV. It is also shown that implementation of the calculated coefficients into the computation of the tissue weighting factors and the adult reference computational phantoms of ICRP Publication 103 does not significantly influence the effective dose conversion coefficients of the environment. Consequently, the coefficients shown in this paper could be applied for the evaluation of effective doses, as defined according to both recommendations of ICRP Publications 103 and 60. [ABSTRACT FROM AUTHOR]

Internal dosimetry in non-human biota is desirable from the viewpoint of radiation protection of the environment. The International Commission on Radiological Protection (ICRP) proposed Reference Animals and Plants using simplified models, such as ellipsoids and spheres and calculated absorbed fractions (AFs) for whole bodies. In this study, photon and electron AFs in whole bodies of voxel-based rat and frog models have been calculated and compared with AFs in the reference models. It was found that the voxel-based and the reference frog (or rat) models can be consistent for the whole-body AFs within a discrepancy of 25 %, as the source was uniformly distributed in the whole body. The specific absorbed fractions (SAFs) and S values were also evaluated in whole bodies and all organs of the voxel-based frog and rat models as the source was distributed in the whole body or skeleton. The results demonstrated that the whole-body SAFs reflect SAFs of all individual organs as the source was uniformly distributed per mass within the whole body by about 30 % uncertainties with exceptions for body contour (up to −40 %) for both electrons and photons due to enhanced radiation leakages, and for the skeleton for photons only (up to +185 %) due to differences in the mass attenuation coefficients. For nuclides such as 90Y and 90Sr, which were concentrated in the skeleton, there were large differences between S values in the whole body and those in individual organs, however the whole-body S values for the reference models with the whole body as the source were remarkably similar to those for the voxel-based models with the skeleton as the source, within about 4 and 0.3 %, respectively. It can be stated that whole-body SAFs or S values in simplified models without internal organs are not sufficient for accurate internal dosimetry because they do not reflect SAFs or S values of all individual organs as the source was not distributed uniformly in whole body. Thus, voxel-based models would be good candidates for dosimetry in non-human biota if further accuracy in environmental dosimetry is desired. [ABSTRACT FROM PUBLISHER]

Acetylation of lysine residues, one of the most common protein post-transcriptional modifications, is thought to regulate protein affinity with other proteins or nucleotides. Experimentally, the effects of acetylation have been studied using recombinant mutants in which lysine residues (K) are substituted with glutamine (Q) as a mimic of acetyl lysine (KQ mutant), or with arginine (R) as a mimic of nonacetylated lysine (KR mutant). These substitutions, however, have not been properly validated. The effects lysine acetylation on Ku, a multifunctional protein that has been primarily implicated in DNA repair and cell survival, are characterized herein using a series of computer simulations. The binding free energy was reduced in the KQ mutant, while the KR mutant had no effect, which is consistent with previous experimental results. Unexpectedly, the binding energy between Ku and DNA was maintained at almost the same level as in the wild type protein despite full acetylation of the lysine residues. These results suggest that the effects of acetylation may be overestimated when the KQ mutant is used as a mimic of the acetylated protein. © 2011 Wiley Periodicals, Inc. J Comput Chem 2012 [ABSTRACT FROM AUTHOR]

In the Japan Atomic Energy Agency, several studies have been conducted on the use of voxel models for internal dosimetry. Absorbed fractions (AFs) and S values have been evaluated for preclinical assessments of radiopharmaceuticals using human voxel models and a mouse voxel model. Computational calibration of in vivo measurement system has been also made using Japanese and Caucasian voxel models. In addition, for radiation protection of the environment, AFs have been evaluated using a frog voxel model. Each study was performed by using Monte Carlo simulations. Consequently, it was concluded that these data of Monte Carlo simulations and voxel models could adequately reproduce measurement results. Voxel models were found to be a significant tool for internal dosimetry since the models are anatomically realistic. This fact indicates that several studies on correction of the in vivo measurement efficiency for the variability of human subjects and interspecies scaling of organ doses will succeed. [ABSTRACT FROM PUBLISHER]

Radial energy deposition distribution, the distribution of DNA strand breaks and their yields were simulated by Monte Carlo track structure simulation for C and Ne ions with the same linear energy transfer (LET) around 450 keV/μm. The radial DNA damage distribution shows different pattern for C and Ne ions. Double strand break (DSB) are mostly formed in the central area, while the single strand break (SSB) tends to spread to the surrounding area. It is also shown that the production efficiency of the SSB and DSB depends on the radial distance. This result shows reasonable agreement with the recently obtained experimental observation, which indicates that different types of DNA damage shows different distribution patterns around C and Ne ion paths in cell nuclei. [ABSTRACT FROM PUBLISHER]

The internal exposures of the patients in nuclear medicine can be calculated based on the equations and data in ICRP Publications 53 and 80. Physical and biological parameters are used for the calculation, and both include uncertainties. Physical parameters can be considered as more precise than biological parameters, so that uncertainties originated from biological parameters are more important. Absorbed fractions (AFs) have been calculated by Monte-Carlo method using medical internal radiation dose (MIRD)-type mathematical phantoms. They depend on the shapes and sizes of the phantoms used in simulations. For estimating shape- and size-related uncertainties, AFs of pairs of source regions and target tissues of the patient-injected 99mTc-MDP were calculated by using EGS4 codes and a voxel phantom of Japanese male. By simply resizing the voxels of the phantom, the dependencies of size for AFs were calculated, and the uncertainties caused by the cumulated activities in source regions were also estimated by assuming these parameters distributions as Gaussian. [ABSTRACT FROM AUTHOR]

In recent years, concern has been raised about patient-specific doses due to the increased use of PET imaging. It is of scientific and practical interest for the accurate quantification of the doses to patients administered a radiopharmaceutical for PET imaging. In the present study, Monte Carlo simulations have been carried out to evaluate S values—the mean absorbed dose to the target region per unit cumulated activity in the source region—for positron emitters in the brain, heart and the urinary bladder content. The positron emitters considered were four radionuclides that are frequently used for PET imaging: 11C, 13N, 15O and 18F. S values were evaluated for the Medical Internal Radiation Dose S type mathematical phantom and the adult voxel phantoms developed at the Japan Atomic Energy Research Institute (JAERI). Consequently, Monte Carlo simulation and voxel phantoms were found to be useful in the evaluation of the beta dose to organs, in particular to hollow organs such as the urinary bladder. It was also demonstrated that the self-dose S values largely depend on the beta-ray energy and the mass of each target region. [ABSTRACT FROM AUTHOR]

As the conventional graphical user interface (GUI) associated with DOSXYZnrc or BEAMnrc is unable to define specific structures such as gross tumor volume (GTV) on computed tomography (CT) data, the quantitative analysis of doses in the form of dose-volume histograms (DVHs) is difficult. The purpose of this study was to develop an interface that enables us to analyze the results of DOSXYZnrc output with a commercial radiation treatment planning (RTP) system and to investigate the validity of the system. Interface software to visualize three-dimensional radiotherapy Monte Carlo (MC) dose data from DOSXYZnrc on the XiO RTP system was developed. To evaluate the interface, MC doses for a variety of photon energies were calculated using the CT data of a thorax phantom and a uniform phantom as well as data from patients with lung tumors. The dose files were analyzed on the XiO RTP system in the form of isodose distributions and DVHs. In all cases, the XiO RTP system perfectly displayed the MC doses for quantitative evaluation in the form of differential and integral DVHs. Three-dimensional display of DOSXYZnrc doses on a dedicated RTP system could provide all the existing facilities of the system for quantitative dose analysis. [ABSTRACT FROM AUTHOR]

Clustered DNA damage sites induced by ionizing radiation have been suggested to have serious consequences to organisms, such as cancer, due to their reduced probability to be repaired by the enzymatic repair machinery of the cell. Although experimental results have revealed that clustered DNA damage sites effectively retard the efficient function of repair enzymes, it remains unclear as to what particular factors influence this retardation. In this study, approaches based on molecular dynamics (MD) simulation have been applied to examine conformational changes and energetic properties of DNA molecules containing clustered damage sites consisting of two lesioned sites, namely 7,8-dihydro-8-oxoguanine (8-oxoG) and apurinic/apyrimidinic (AP) site, located within a few base pairs of each other. After 1 ns of MD simulation, one of the six DNA molecules containing a clustered damage site develops specific characteristic features: sharp bending at the lesioned site and weakening or complete loss of electrostatic interaction energy between 8-oxoG and bases located on the complementary strand. From these results it is suggested that these changes would make it difficult for the repair enzyme to bind to the lesions within the clustered damage site and thereby result in a reduction of its repair capacity. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 788–798, 2005 [ABSTRACT FROM AUTHOR]

Purpose: To study DNA strand breaks induced by direct energy deposition by photo- and Auger electrons ejected following K-shell photoabsorption of DNA constituent atoms (carbon, nitrogen, oxygen and phosphorus). Method: Using a Monte Carlo code which has been developed to simulate the photoelectric effect on plasmid DNA pBR322, the energy deposition pattern of secondary electrons ejected after photoabsorption in DNA constituent atoms (not including the hydration shell) was calculated. Experimentally obtained X-ray absorption near edge structures were considered of the cross-sections at the K-shell resonant absorption (1s&rarrα*) of carbon, nitrogen and oxygen, and the K-shell resonant absorption (1s→α*) of phosphorus. Direct energy deposition by secondary electrons was scored using two different DNA models with and without the hydrated shell. The yields of SSB, DSB per photoabsorption events as well as break complexity were estimated for monochromatic X-rays around the K-edges of DNA constituent atoms (200-3000 eV). Result: Higher SSB and DSB yields were obtained below the carbon, nitrogen and oxygen K-edges compared to at or above the resonance, and at the K-shell resonant absorption of phosphorus compared to below the resonance. The number of electrons with sufficient energy to induce strand breaks was found to change depending on the photon energy. Electrons with 120 and 250 eV are shown to be rather more effective in SSB and DSB induction than electrons with higher energy. Inclusion of hydrated water in the DNA volume did not affect the photon energy dependence of the strand break yields. Conclusion: The small difference of photon energies around K-absorption edges of the carbon, nitrogen, oxygen and phosphorus is indicated to induce variation in strand break yields by direct effect. Higher SSB and DSB induction efficiencies could be due to a higher yield of more than two electrons with around 120 eV to 250 eV per photoabsorption event. [ABSTRACT FROM AUTHOR]

The radiation-induced process of strand breaks on pBR322 plasmid DNA in aqueous solution for different energy electrons was studied by Monte Carlo simulation. Assumptions of induction mechanisms of single- and double-strand breaks (SSBs and DSBs) used in the simulation are that SSB is induced by OH or H reaction with DNA and that DSB is induced by two SSBs on the opposite strands within 10 bp. Dose-response relationships of SSBs and DSBs were demonstrated for monoenergetic electrons of 100 eV, 10 keV, 1 keV and 1 MeV, and the yields of SSB and DSB were calculated. The dose-response relationships of SSBs and DSBs can be fitted by linear and linear-quadratic functions, respectively. The ratio of quadratic to linear components of DSB induction changes due to the electron energy. A high contribution of the linear component is observed for 1 keV electrons in the dose range below 160 Gy. The yields of SSBs and DSBs for all examined electron energies lie well within the experimental data when the probability of strand-break induction by OH and H is assumed to be around 0.1–0.2. The yield of SSBs has a minimum at 1 keV, while the yield of DSBs has a maximum at 1 keV in the examined energies. The strand breaks are formed most densely for 1 keV electrons. [ABSTRACT FROM AUTHOR]