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Cesium-bearing microparticles (Cs-BMPs) can reach the human respiratory system after inhalation, resulting in chronic local internal exposure. We previously investigated the spatial distribution of DNA damage induced in areas around a Cs-BMP; however, the biological impacts have not been fully clarified due to the limited amount of data. Here, we investigated the inflammatory signaling and DNA damage responses after local exposure to a Cs-BMP in vitro. We used two normal human lung cell lines, i.e., lung fibroblast cells (WI-38) and bronchial epithelial cells (HBEC3-KT). After 24 h exposure to a Cs-BMP, inflammation was evaluated by immunofluorescent staining for nuclear factor κB (NF-κB) p65 and cyclooxygenase 2 (COX-2). The number of DNA double-strand breaks (DSBs) was also detected by means of phospholylated histone H2AX (γ-H2AX) focus formation assay. Cs-BMP exposure significantly increased NF-κB p65 and COX-2 expressions, which were related to the number of γ-H2AX foci in the cell nuclei. Compared to the uniform (external) exposure to 137Cs γ-rays, NF-κB tended to be more activated in the cells proximal to the Cs-BMP, while both NF-κB p65 and COX-2 were significantly activated in the distal cells. Experiments with chemical inhibitors for NF-κB p65 and COX-2 suggested the involvement of such inflammatory responses both in the reduced radiosensitivity of the cells proximal to Cs-BMP and the enhanced radiosensitivity of the cells distal from Cs-BMP. The data show that local exposure to Cs-BMP leads to biological effects modified by the NF-κB pathway, suggesting that the radiation risk for Cs-BMP exposure can differ from that estimated based on conventional uniform exposure to normal tissues.

Altered gene expression is a common feature of tumor cells after irradiation. Our previous study showed that this phenomenon is not only an acute response to cytotoxic stress, instead, it was persistently detected in tumor cells that survived 10 Gy irradiation (IR cells). The current understanding is that DNA double-strand breaks (DSBs) are recognized by the phosphorylation of histone H2AX (H2AX) and triggers the ataxia-telangiectasia mutated (ATM) protein or the ATM- and Rad3-related (ATR) pathway, which activate or inactivate the DNA repair or apoptotic or senescence related molecules and causes the expression of genes in many instances. However, because changes in gene expression persist after passaging in IR cells, it may be due to the different pathways from these transient intracellular signaling pathways caused by DSBs. We performed microarray analysis of 30,000 genes in radiation-surviving cells (H1299-IR and MCF7-IR) and found an interesting relation between altered genes and their chromosomal loci. These loci formed a cluster on the chromosome, especially on 1q21 and 6p21-p22 in both irradiated cell lines. These chromosome sites might be regarded as “radio-fragile” sites.

In this study, we proposed and evaluated the validity of an optimized size-specific dose estimate, a widely used index of radiation dose in X-ray computed tomography (CT) examinations. Based on miscentering correction of scout images, we determined the appropriate conversion factors (CF) by using a phantom. Scans were conducted using a multi-detector CT system (Aquilion ONE, Canon Medical Systems). Four cylindrical phantoms were taken in the anteroposterior (AP) and axial directions to determine the relationship between pixel value and water-equivalent length (L-w). In the AP scout image, the pixel values at the selected slice positions were converted to L-w to calculate the water-equivalent diameter (D-w). The CF was derived from D-w and CF values before and after miscentering correction was calculated. Finally, the CF values were compared to those calculated from the axial image using the conventional methodology of the American Association of Physicists in Medicine. Before miscentering correction, the maximum difference between the CF values of the axial and scout images was 7.26%. However, after miscentering correction, the maximum difference was 1.34%. Validation using a whole-body phantom generally revealed low maximum differences between the CF from the axial image and the values from the miscentering-corrected scout images. These were 2.41% in the chest, 6.30% in the upper abdomen, 1.43% in the abdomen, and 2.45% in the pelvic region. Consequently, we concluded that our miscentering correction method for deriving the appropriate CF values based on scout images is advantageous.

In advanced radiotherapy, intensity modulated radiation fields and complex dose-delivery are utilized to prescribe higher doses to tumours. Here, we investigated the impact of modulated radiation fields on radio-sensitivity and cell recovery during dose delivery. We generated experimental survival data after single-dose, split-dose and fractionated irradiation in normal human skin fibroblast cells (AGO1522) and human prostate cancer cells (DU145). The dose was delivered to either 50% of the area of a T25 flask containing the cells (half-field) or 100% of the flask (uniform-field). We also modelled the impact of dose-rate effects and intercellular signalling on cell-killing. Applying the model to the survival data, it is found that (i) in-field cell survival under half-field exposure is higher than uniform-field exposure for the same delivered dose; (ii) the importance of sub-lethal damage repair (SLDR) in AGO1522 cells is reduced under half-field exposure; (iii) the yield of initial DNA lesions measured with half-field exposure is smaller than that with uniform-field exposure. These results suggest that increased cell survival under half-field exposure is predominantly attributed not to rescue effects (increased SLDR) but protective effects (reduced induction of initial DNA lesions). In support of these protective effects, the reduced DNA damage leads to modulation of cell-cycle dynamics, i.e., less G1 arrest 6 h after irradiation. These findings provide a new understanding of the impact of dose-rate effects and protective effects measured after modulated field irradiation.

Insoluble radioactive microparticles emitted by the incident at the Fukushima nuclear power plant have drawn keen interests from the viewpoint of radiation protection. Cs-bearing particles have been assumed to adhere in the long term to trachea after aspirated into respiratory system, leading to heterogeneous dose distribution within healthy tissue around the particles. However, the biological effects posed by an insoluble radioactive particle remain unclear. Here, we show cumulative DNA damage in normal human lung cells proximal and distal to the particle (β-ray and γ-ray-dominant areas, respectively) under localized chronic exposure in comparison with uniform exposure. We put a Cs-bearing particle into a microcapillary tip and placed it onto a glass-base dish containing fibroblast or epithelial cells cultured in vitro. A Monte Carlo simulation with PHITS code provides the radial distribution of absorbed dose-rate around the particle, and subsequently we observed a significant change in nuclear γ-H2AX foci after 24 h or 48 h exposure to the particle. The nuclear foci in the cells distal to the particle increased even under low-dose-rate exposure compared with uniform exposure to 137Cs γ-rays, which was suppressed by a treatment with a scavenger of reactive oxygen species. In contrast, such focus formation was less manifested in the exposed cells proximal to the particle compared with uniform exposure. These data suggest that the localized exposure to a Cs-bearing particle leads to not only disadvantage to distal cells but also advantage to proximal cells. This study is the first to provide quantitative evaluation for the spatial distribution of DNA double strand breaks after the heterogeneous chronic exposure to a Cs-bearing particle in comparison with uniform Cs exposure.

We provide details of the dual-focal 3D tracking and pixel intensity calibration (DuFT) system used to record gene expression in targeted areas on the skin of freely moving mice. The accuracy of the 3D position calculation was determined by placing a scintillator on the calibration disk at various known locations within the recording cage. The height of the disk was varied from the bottom (Z = 0 cm) to the top (Z = 30 cm). The distance from the central axis range from near the center (R = 1 cm) to near to edge (R = 5 cm). The mean deviation between the known and calculated position was .31 ± 0.16 mm. The maximum deviation was less than .86 mm. The results indicate that the location of a scintillator within the recording cage imaged with two cameras can be calculated with submillimeter accuracy. We hope that our methods can be applied to improve automatic (even real-time) tracking of various animals in vivo.

In radiotherapy, cancer stem cells (CSCs) are well recognized as one of the radioresistant cell types. Even in a small subpopulation, CSCs may have an influence on tumor control probability, represented by cell killing after irradiation. However, the relationship between the percentage content of CSCs and the cell survival dose–response curve has not yet been quantitatively clarified. In this study, we developed a cell-killing model for two cell populations (CSCs and progeny cells) to predict the surviving fractions, and compared it with the conventional linear–quadratic (LQ) model. Three prostate cancer cell lines (DU145, PC3 and LNCaP) were exposed to X-rays at doses ranging from 0 to 10 Gy. After the irradiation, we performed clonogenic survival assays to generate the cell survival curves, and carried out flow-cytometric analyses to estimate the percentage content of CSCs for each cell line. The cell survival curves for DU145 cells and PC3 cells seemed not to follow the conventional LQ model in the high dose range (>8 Gy). However, the outputs of the developed model agreed better with the experimental cell survival curves than those of the LQ model. The percentage content of CSCs predicted by the developed model was almost coincident with the measured percentage content for both DU145 cells and PC3 cells. The experiments and model analyses indicate that a small subpopulation of radioresistant CSCs has lower radiosensitivity in the high-dose range, which may lessen the clinical outcome for patients with prostate cancer after high-dose radiation therapy.

Hyaluronan synthesis inhibitor 4-methylumbelliferone (4-MU) is a candidate of radiosensitizers which enables both anti-tumour and anti-metastasis effects in X-ray therapy. The curative effects under such 4-MU administration have been investigated in vitro; however, the radiosensitizing mechanisms remain unclear. Here, we investigated the radiosensitizing effects under 4-MU treatment from cell experiments and model estimations. We generated experimental surviving fractions of human fibrosarcoma cells (HT1080) after 4-MU treatment combined with X-ray irradiation. Meanwhilst, we also modelled the pharmacological effects of 4-MU treatment and theoretically analyzed the synergetic effects between 4-MU treatment and X-ray irradiation. The results show that the enhancement of cell killing by 4-MU treatment is the greatest in the intermediate dose range of around 4 Gy, which can be reproduced by considering intercellular communication (so called non-targeted effects) through the model analysis. As supposed to be the involvement of intercellular communication in radiosensitization, the oxidative stress level associated with reactive oxygen species (ROS), which leads to DNA damage induction, is significantly higher by the combination of 4-MU treatment and irradiation than only by X-ray irradiation, and the radiosensitization by 4-MU can be suppressed by the ROS inhibitors. These findings suggest that the synergetic effects between 4-MU treatment and irradiation are predominantly attributed to intercellular communication and provide more efficient tumour control than conventional X-ray therapy.

DNA double-strand breaks (DSBs) are thought to be the main cause of cell death after irradiation. In this study, we estimated the probability distribution of the number of DSBs per cell nucleus by considering the DNA amount in a cell nucleus (which depends on the cell cycle) and the statistical variation in the energy imparted to the cell nucleus by X-ray irradiation. The probability estimation of DSB induction was made following these procedures: (i) making use of the Chinese Hamster Ovary (CHO)-K1 cell line as the target example, the amounts of DNA per nucleus in the logarithmic and the plateau phases of the growth curve were measured by flow cytometry with propidium iodide (PI) dyeing; (ii) the probability distribution of the DSB number per cell nucleus for each phase after irradiation with 1.0 Gy of 200 kVp X-rays was measured by means of γ-H2AX immunofluorescent staining; (iii) the distribution of the cell-specific energy deposition via secondary electrons produced by the incident X-rays was calculated by WLTrack (in-house Monte Carlo code); (iv) according to a mathematical model for estimating the DSB number per nucleus, we deduced the induction probability density of DSBs based on the measured DNA amount (depending on the cell cycle) and the calculated dose per nucleus. The model exhibited DSB induction probabilities in good agreement with the experimental results for the two phases, suggesting that the DNA amount (depending on the cell cycle) and the statistical variation in the local energy deposition are essential for estimating the DSB induction probability after X-ray exposure.

In this paper, we compare two radiation effect models: the average surviving fraction (ASF) model and the integral biologically effective dose (IBED) model for deriving the optimal irradiation scheme and show the superiority of ASF. Minimizing the effect on an organ at risk (OAR) is important in radiotherapy. The biologically effective dose (BED) model is widely used to estimate the effect on the tumor or on the OAR, for a fixed value of dose. However, this is not always appropriate because the dose is not a single value but is distributed. The IBED and ASF models are proposed under the assumption that the irradiation is distributed. Although the IBED and ASF models are essentially equivalent for deriving the optimal irradiation scheme in the case of uniform distribution, they are not equivalent in the case of non-uniform distribution. We evaluate the differences between them for two types of cancers: high α/β ratio cancer (e.g. lung) and low α/β ratio cancer (e.g. prostate), and for various distributions i.e. various dose–volume histograms. When we adopt the IBED model, the optimal number of fractions for low α/β ratio cancers is reasonable, but for high α/β ratio cancers or for some DVHs it is extremely large. However, for the ASF model, the results keep within the range used in clinical practice for both low and high α/β ratio cancers and for most DVHs. These results indicate that the ASF model is more robust for constructing the optimal irradiation regimen than the IBED model.

Purpose High-dose-rate irradiation with 6 MV linac X-rays is a wide-spread means to treat cancer tissue in radiotherapy. The treatment planning relies on a mathematical description of surviving fraction (SF), such as the linear-quadratic model (LQM) formula. However, even in the case of high-dose-rate treatment, the repair kinetics of DNA damage during dose-delivery time plays a function in predicting the dose-SF relation. This may call the SF model selection into question when considering the dose-delivery time or dose-rate effects (DREs) in radiotherapy and in vitro cell experiments. In this study, we demonstrate the importance of dose-delivery time at high-dose-rate irradiations used in radiotherapy by means of Bayesian estimation. Methods To evaluate the model selection for SF, three types of models, the LQM and two microdosimetric-kinetic models with and without DREs (MKMDR and MKM) were applied to describe in vitro SF data (our work and references). The parameters in each model were evaluated by a Markov chain Monte Carlo (MCMC) simulation. Results The MCMC analysis shows that the cell survival curve by the MKMDR fits the experimental data the best in terms of the deviance information criterion (DIC). In the fractionated regimen with 30 fractions to a total dose of 60 Gy, the final cell survival estimated by the MKMDR was higher than that by the LQM. This suggests that additional fractions are required for attaining the total dose equivalent to yield the same effect as the conventional regimen using the LQM in fractionated radiotherapy. Conclusions Damage repair during dose-delivery time plays a key role in precisely estimating cell survival even at a high dose rate in radiotherapy. Consequently, it was suggested that the cell-killing model without repair factor during a short dose-delivery time may overestimate actual cell killing in fractionated radiotherapy. This article is protected by copyright. All rights reserved.

In the northern part of Japan, close cooperation is essential in preparing for any possible emergency response to radiation accidents because several facilities, such as the Low-Level Radioactive Waste Disposal Facility, the MOX Fuel Fabrication Plant and the Vitrified Waste Storage Center, exist in Rokkasho Village (Aomori Prefecture). After the accident at Fukushima Daiichi Nuclear Power Plant in 2011, special attention should be given to the relationship between radiation and human health, as well as establishing a system for managing with a radiation emergency. In the area of Hokkaido and Aomori prefectures in Japan, since 2008 an exchange meeting between Hokkaido University and Hirosaki University has been held every year to have opportunities to discuss radiation effects on human health and to collect the latest news on monitoring environmental radiation. This meeting was elevated to an international meeting in 2014 titled “Educational Symposium on Radiation and Health (ESRAH) by Young Scientists”. ...

Radiation weighting factor wR for photons and electrons has been defined as unity independently of the energy of the particles. However, the biological effects depend on the incident energies according to in vitro experimental data. In this study, we have quantified the energy concentration along electron tracks in terms of dose-mean lineal energy (yD) on chromosome (micro-meter) and DNA (nano-meter) order scales by Monte Carlo simulations, and evaluated the impact of photon energies on DNA double-strand break (DNA-DSB) induction from an experimental study of irradiated cells. Our simulation result shows that the yD values for diagnostic X-rays (60–250 kVp) are higher than that for therapeutic X-rays (linac 6 MV), which agrees well with the tissue equivalent proportional counter (TEPC) measurements. The relation between the yD values and the numbers of γ-H2AX foci for various photon energy spectra suggests that low energy X-rays induce DNA-DSB more efficiently than higher energy X-rays even at the same absorbed dose (e.g., 1.0 Gy). The relative biological effectiveness based on DNA-DSBs number (RBEDSB) is proportionally enhanced as the yD value increases, demonstrating that the biological impact of the photon irradiation depends on energy concentration along radiation tracks of electrons produced in the bio-tissues. Ultimately, our study implies that the value of wR for photons varies depending on their energies.

Hypoxic cancer cells within solid tumours show radio-resistance, leading to malignant progression in fractionated radiotherapy. When prescribing dose to tumours under heterogeneous oxygen pressure with intensity-modulated radiation fields, intercellular signalling could have an impact on radiosensitivity between in-field and out-of-field (OF) cells. However, the impact of hypoxia on radio-sensitivity under modulated radiation intensity remains to be fully clarified. Here, we investigate the impact of hypoxia on in-field and OF radio-sensitivities using two types of cancer cells, DU145 and H1299. Using a nBIONIX hypoxic culture kit and a shielding technique to irradiate 50% of a cell culture flask, oxygen enhancement ratios for double-strand breaks (DSB) and cell death endpoints were determined. These in vitro measurements indicate that hypoxia impacts OF cells, although the hypoxic impacts on OF cells for cell survival were dose-dependent and smaller compared to those for in-field and uniformly irradiated cells. These decreased radio-sensitivities of OF cells were shown as a consistent tendency for both DSB and cell death endpoints, suggesting that radiation-induced intercellular communication is of importance in advanced radiotherapy dose-distributions such as with intensity-modulated radiotherapy.

Understanding of hydrogen accumulation behavior in tungsten deposits is important from viewpoints of tritium economy and tritium safety in fusion reactors. Some reports indicate that a large amount of hydrogen isotope is incorporated into tungsten deposits growing by hydrogen plasma sputtering. However, the mechanism of hydrogen incorporation is not clarified yet. In this work, tungsten deposits were formed at different circumstances in the sputtering device and the amount of incorporated hydrogen was measured. The implantation of hydrogen reflected from the sputtering target was mainly contributed to the hydrogen incorporation. The contribution of the implantation of reactive hydrogen from plasma was smaller than that of the reflected hydrogen in the experimental condition. A detectable amount of tungsten deposits was formed even in the shadow region from the sputtering target. This suggests that a certain amount of tungsten atoms, which lost its initial energy by collision with molecular hydrogen, diffuses in the gas phase and adheres in the shadow region.

Development of tritium transport model in natural soil is an important issue from a viewpoint of safety of fusion reactors. The spill of a large amount of tritiated water to the environment is a concern accident because huge tritiated water is handled in a fusion plant. In this work, a simple tritium transport model was proposed based on the tritium transport model in porous materials. The overall mass transfer coefficient representing isotope exchange reaction between tritiated water and structural water in soil particles was obtained by numerically analyzing the result of the percolation experiment of tritiated water into the soil packed bed. Saturated hydraulic conductivity in the natural soil packed bed was obtained to be 0.033 mm/s. By using this value, the overall mass transfer capacity coefficients representing the isotope exchange reaction between tritiated water percolating through the packed bed and overall structural water on soil particles was determined to be 6.0 × 10−4 1/s. This value is much smaller than the mass transfer capacity coefficient between tritiated water vapor and water on concrete material and metals.

Gold nanoparticles (GNPs) have been recognized as a promising candidate for a radiation sensitizer. A proton beam incident on a GNP can produce secondary electrons, resulting in an enhancement of the dose around the GNP. However, little is known about the spatial distribution of dose enhancement around the GNP, especially in the direction along the incident proton. The purpose of this study is to determine the spatial distribution of dose enhancement by taking the incident direction into account. Two steps of calculation were conducted using the Geant4 Monte Carlo simulation toolkit. First, the energy spectra of 100 and 195 MeV protons colliding with a GNP were calculated at the Bragg peak and three other depths around the peak in liquid water. Second, the GNP was bombarded by protons with the obtained energy spectra. Radial dose distributions were computed along the incident beam direction. The spatial distributions of the dose enhancement factor (DEF) and subtracted dose (Dsub) were then evaluated. The spatial DEF distributions showed hot spots in the distal radial region from the proton beam axis. The spatial Dsub distribution isotropically spread out around the GNP. Low energy protons caused higher and wider dose enhancement. The macroscopic dose enhancement in clinical applications was also evaluated. The results suggest that the consideration of the spatial distribution of GNPs in treatment planning will maximize the potential of GNPs.

American Association of Physicists in Medicine (AAPM) Report No.204 recommends the size-specific dose estimates (SSDE), wherein SSDE=computed tomography dose index-volume (CTDIvol )×size correction factor (SCF), as an index of the CT dose to consider patient thickness. However, the study on SSDE has not been made yet for area detector CT (ADCT) device such as a 320-row CT scanner. The purpose of this study was to evaluate the SCF values for ADCT by means of a simulation technique to look into the differences in SCF values due to beam width. In the simulation, to construct the geometry of the Aquilion ONE X-ray CT system (120 kV), the dose ratio and the effective energies were measured in the cone angle and fan angle directions, and these were incorporated into the simulation code, Electron Gamma Shower Ver.5 (EGS5). By changing the thickness of a PMMA phantom from 8 cm to 40 cm, CTDIvol and SCF were determined. The SCF values for the beam widths in conventional and volume scans were calculated. The differences among the SCF values of conventional, volume scans, and AAPM were up to 23.0%. However, when SCF values were normalized in a phantom of 16 cm diameter, the error tended to decrease for the cases of thin body thickness, such as those of children. It was concluded that even if beam width and device are different, the SCF values recommended by AAPM are useful in clinical situations.

Radio-resistance induced under low oxygen pressure plays an important role in malignant progression in fractionated radiotherapy. For the general approach to predict cell killing under hypoxia, cell-killing models (e.g. the Linear-Quadratic model) have to be fitted to in vitro experimental survival data for both normoxia and hypoxia to obtain the oxygen enhancement ratio (OER). In such a case, model parameters for every oxygen condition needs to be considered by model-fitting approaches. This is inefficient for fractionated irradiation planning. Here, we present an efficient model for fractionated radiotherapy the integrated microdosimetric-kinetic model including cell-cycle distribution and the OER at DNA double-strand break endpoint (OERDSB). The cell survival curves described by this model can reproduce the in vitro experimental survival data for both acute and chronic low oxygen concentrations. The OERDSB used for calculating cell survival agrees well with experimental DSB ratio of normoxia to hypoxia. The important parameters of the model are oxygen pressure and cell-cycle distribution, which enables us to predict cell survival probabilities under chronic hypoxia and chronic anoxia. This work provides biological effective dose (BED) under various oxygen conditions including its uncertainty, which can contribute to creating fractionated regimens for multi-fractionated radiotherapy. If the oxygen concentration in a tumor can be quantified by medical imaging, the present model will make it possible to estimate the cell-killing and BED under hypoxia in more realistic intravital situations.

Particle beam therapy (PBT), including proton and carbon ion therapy, is an emerging innovative treatment for cancer patients. Due to the high cost of and limited access to treatment, meticulous selection of patients who would benefit most from PBT, when compared with standard X-ray therapy (XRT), is necessary. Due to the cost and labor involved in randomized controlled trials, the model-based approach (MBA) is used as an alternative means of establishing scientific evidence in medicine, and it can be improved continuously. Good databases and reasonable models are crucial for the reliability of this approach. The tumor control probability and normal tissue complication probability models are good illustrations of the advantages of PBT, but pre-existing NTCP models have been derived from historical patient treatments from the XRT era. This highlights the necessity of prospectively analyzing specific treatment-related toxicities in order to develop PBT-compatible models. An international consensus has been reached at the Global Institution for Collaborative Research and Education (GI-CoRE) joint symposium, concluding that a systematically developed model is required for model accuracy and performance. Six important steps that need to be observed in these considerations include patient selection, treatment planning, beam delivery, dose verification, response assessment, and data analysis. Advanced technologies in radiotherapy and computer science can be integrated to improve the efficacy of a treatment. Model validation and appropriately defined thresholds in a cost-effectiveness centered manner, together with quality assurance in the treatment planning, have to be achieved prior to clinical implementation.

It is important to evaluate the influence of deposition layers formed on plasma facing wall on tritium permeation and tritium retention in the vessel of a fusion reactor from a viewpoint of safety. In this work, tungsten deposition layers having different thickness and porosity were formed on circular nickel plates by hydrogen RF plasma sputtering. Hydrogen permeation experiment was carried out at the temperature range from 250 °C to 500 °C and at hydrogen pressure range from 1013 Pa to 101,300 Pa. The hydrogen permeation flux through the nickel plate with tungsten deposition layer was significantly smaller than that through a bare nickel plate. This indicates that a rate-controlling step in hydrogen permeation was not permeation through the nickel plate but permeation though the deposition layer. The pressure dependence on the permeation flux differed by temperature. Hydrogen permeation flux through tungsten deposition layer is larger than that through tungsten bulk. From analysis of the permeation curves, it was indicated that hydrogen diffusivity in tungsten deposition layer is smaller than that in tungsten bulk and the equilibrium hydrogen concentration in tungsten deposition layer is enormously larger than that in tungsten bulk at same hydrogen pressure.

In this study, tritiated water was poured in a packed bed of natural soil and subsequently distilled water was poured in the bed to recover tritium retained in the soil at room temperature. From tr...

Tungsten (W) deposits were formed by hydrogen plasma sputtering and blisters were observed on the surface. The W deposits and W foils were exposed to deuterium ions with 2 keV-D2+ to doses of 1.0 × 1021 D2+/m2 at 294 and 773 K in addition to 573 K in the present authors’ previous work. Hydrogen isotopes release behaviors from the W deposits and W foils were observed by the thermal desorption spectroscopy method. The amount of deuterium released from the W deposit was considerably larger than that from W foil. The obtained deuterium retention in D/m2 was in the range of deuterium retention in polycrystalline tungsten. Not only implanted deuterium but also hydrogen, which was incorporated during the sputtering-deposition process, were released from the W deposits. A hydrogen release peak at around 1100 K was observed for the W deposits. This is considered to be due to the rupture of the blisters.

To clarify the influence of bio-cells exposed to ionizing radiations, the densely populated pattern of the ionization in the cell nucleus is of importance because it governs the extent of DNA damage which may lead to cell lethality. In this study, we have conducted a cluster analysis of ionization and excitation events to estimate the number of double-strand breaks (DSBs) induced by electron tracks. A Monte Carlo simulation for electrons in liquid water was performed to determine the spatial location of the ionization and excitation events. The events were divided into clusters by using the density-based spatial clustering of applications with noise (DBSCAN) algorithm. The algorithm enables us to sort out the events into the groups (clusters) in which a minimum number of neighboring events are contained within a given radius. For evaluating the number of DSBs in the extracted clusters, we have introduced an aggregation index (AI). The computational results show that a sub-keV electron produces DSBs in a dense formation more effectively than higher energy electrons. The root-mean square radius (RMSR) of the cluster size is below 5 nm, which is smaller than the chromatin fiber thickness. It was found that this size of clustering events has a high possibility to cause lesions in DNA within the chromatin fiber site.

Purpose: In radiation therapy, gold nanoparticles (GNPs) are regarded as a promising radiosensitizer candidate. Several studies have revealed a dose enhancement by GNPs in X-ray and even proton irradiation. However, these studies have been limited to the depth direction. The dose distribution in both depth and lateral directions is crucial to evaluate the full radio sensitizing effect. The purpose of this study is to estimate the dose distribution around a GNP in terms of ejected electrons. Methods: The Geant4 Monte Carlo simulation toolkit was used to evaluate the energy deposition of electrons produced by a GNP. A 20 nm diameter spherical GNP was located in a water box and proton beams were incident unidirectionally. The energy deposition and location of produced electrons were tallied by 5 nm width water slabs at a variety of depths behind the GNP. The radial dose distribution was obtained in each slab. Results: The largest radial dose was observed in the slab closest to the GNP. At the slabs deeper than 90 nm, the dose in the radial direction within 10 nm from the beam direction was found to be smaller than that without GNP. This is because the presence of a GNP decreases the dose behind the GNP, forming a dose shadow. The dose enhancement both in depth and lateral directions was shown in surrounding areas. The area of distribution became larger as the absorbed dose decreased. Conclusion: The dose distribution around a GNP was estimated by a simulation study. The dose enhancement was observed in both the lateral and depth directions. This study will enable us to make use of GNPs as a radiosensitizer in proton therapy.

Inorganic polyphosphate is a linear polymer containing tens to hundreds of orthophosphate residues linked by high-energy phosphoanhydride bonds. Polyphosphate has been recognized as a potent anti-metastasis reagent. However, the molecular mechanism underlying polyphosphate action on cancer cells is poorly understood. In this study, we investigated the involvement of polyphosphate in radio-sensitivity using a human non-small cell lung cancer cell line, H1299. We found that polyphosphate treatment decreases cellular adenosine triphosphate levels, suggesting a disruption of energy metabolism. We also found that the induction of DNA double-strand breaks was enhanced in polyphosphate-treated cells after X-ray irradiation and colony formation assay revealed that cell survival decreased compared with that of the control groups. These findings suggest that polyphosphate is a promising radio-sensitizer for cancer cells. Therefore, we hypothesized that polyphosphate treatment disrupts adenosine triphosphate-mediated energy transfer for cellular survival and DNA repair, thereby reducing the cellular capability to resist X-ray irradiation.

Our purpose in this study was to evaluate the variation in calculated doses caused by respiration in stereotactic body radiotherapy (SBRT) of the lung. The study targeted ten patients who underwent SBRT for lung tumors. CT images were acquired during free breathing and in the inhalation and exhalation phases. We compared the CT image at inhalation with the image at exhalation so as to measure the change in lung volume, variation in the CT value, and displacement of the chest wall. The lung volume change was shown to be correlated with the maximum of the chest wall motion and with the variation in the CT value. A statistically significant difference was observed in the CT values between inhalation and exhalation (p < 0.05). The total dose variation at the isocenter was confined within ±2 %. However, the dose from individual beams can vary significantly when the chest wall moves more than 10 mm in natural breathing.

The microdosimetric-kinetic (MK) model is one of the models that can describe the fraction of cells surviving after exposure to ionizing radiation. In the MK model, there are specific parameters, k and y(D), where k is an inherent parameter to represent the number of potentially lethal lesions (PLLs) and y(D) indicates the dose-mean lineal energy in keV/mu m. Assuming the PLLs to be DNA double-strand breaks (DSBs), the rate equations are derived for evaluating the DSB number in the cell nucleus. In this study, we estimated the ratio of DSBs for two types of photon irradiation (6 MV and 200 kVp X-rays) in Chinese hamster ovary (CHO-K1) cells and human non-small cell lung cancer (H1299) cells by observing the surviving fraction. The estimated ratio was then compared with the ratio of gamma-H2AX foci using immunofluorescent staining. For making a comparison of the number of DSBs among a variety of radiation energy cases, we next utilized the survival data in the literature for both cells exposed to other photon types, such as Co-60 gamma-rays, Cs-137 gamma-rays and 100 kVp X-rays. The ratio of DSBs based on the MK model with conventional data was consistent with the ratio of gamma-H2AX foci numbers, confirming that the gamma-H2AX focus is indicative of DSBs. It was also shown that the larger y(D) is, the larger the DSB number is. These results suggest that k and y(D) represent the characteristics of the surviving fraction and the biological effects for photon irradiation.

DNA strand breaks are induced in cells mainly composed of liquid water along ionizing radiation tracks. For estimating DNA strand break yields, track structures for electrons in liquid water in Monte Carlo simulations are of great importance; however, detailed simulations to obtain both energy deposition and free radical reaction to DNA are time-consuming processes. Here, we present a simple model for estimating yields of single- and double-strand breaks (SSB, DSB, and DSB/SSB ratio) based only on spatial patterns of inelastic interactions (i.e., ionization and electronic excitation) generated by electrons, which are evaluated by the track structure mode of Particle and Heavy Ion Transport code System without analyzing the production and diffusion of free radicals. In the present model, the number of events per track and that of a pair composed of two events within 3.4 nm (10 base pairs) were stochastically sampled for calculating SSB and DSB yields. The results calculated by this model agree well with other simulations and experimental data on the DSB yield and the DSB/SSB ratio for monoenergetic electron irradiation. This model also demonstrates the relative biological effectiveness at the DSB endpoint for various photon irradiations, indicating that the spatial pattern composed of ionization and electronic excitation without physicochemical and chemical stages is sufficient to obtain the impact of electrons on the initial DNA strand break induction.DNA strand breaks are induced in cells mainly composed of liquid water along ionizing radiation tracks. For estimating DNA strand break yields, track structures for electrons in liquid water in Monte Carlo simulations are of great importance; however, detailed simulations to obtain both energy deposition and free radical reaction to DNA are time-consuming processes. Here, we present a simple model for estimating yields of single- and double-strand breaks (SSB, DSB, and DSB/SSB ratio) based only on spatial patterns of inelastic interactions (i.e., ionization and electronic excitation) generated by electrons, which are evaluated by the track structure mode of Particle and Heavy Ion Transport code System without analyzing the production and diffusion of free radicals. In the present model, the number of events per track and that of a pair composed of two events within 3.4 nm (10 base pairs) were stochastically sampled for calculating SSB and DSB yields. The results calculated by this model agree well with ot...

Long-term exposure to low doses of ionizing radiation may adversely affect human cells and tissues of hospital radiation workers, especially peripheral blood cell count. Blood cell count analysis is a useful screening test in a routine medical checkup. A high or low blood cells count even in a healthy-looking subject leads to the suspicion of disease and it should prompt further investigations. This study was aimed to assess the effects of ionizing radiation on the hematological parameters of radiation workers at several governmental hospitals in Indonesia and correlation between years of employment and equivalent dose on one hand and the hematological parameters on the other. It included 74 medical radiation workers occupationally exposed to low doses of ionizing radiation at the Unit of Radiology and Radiotherapy and 83 controls. Fourteen hematological parameters were measured by ABX Micros 60 Hematology analyzer and the correlation between years of employment and equivalent dose as well as hematological parameters on radiation-exposed workers were tested by linear regression analysis test. Our study reported that red blood cell and monocyte counts were significantly higher in radiation-exposed workers compared to controls, whereas white blood cells, hematocrit, mean corpuscular volume, and lymphocytes values were significantly lower in radiation-exposed workers. A significant correlation was observed between equivalent dose and red blood cells (RBCs) parameter (P = 0.001) with a decline in RBC level of 0.541 x 10(6)/mu L per 1 mSv increase of radiation dose. The present study recommends that further studies should use a larger sample size and include various independent variables (genetic polymorphism, chromosome aberration, micronucleus frequency) to study the long-term effects of low-dose radiation exposure on radiation-exposed workers. (C) 2019 Atom Indonesia. All rights reserved

DTN (Delay and Disruption Tolerant Network) is expected to be more effective for such areas that telecommunication infrastructure are heavily damaged by a huge earthquake and tsunami, because it can be applied to worse circumstances that communication delays and disruptions occur. This paper proposes the method that improves power utilization efficiency in DTN communication for mobile nodes in shelters by reducing communication between nodes adjusting to message ferry movement.

Hyper-radiosensitivity (HRS) is a well-known bioresponse under low-dose or low-dose-rate exposures. Although disorder of the DNA repair function, non-targeted effects and accumulation of cells in G2 have been experimentally observed, the mechanism for inducing HRS by long-term irradiation is still unclear. On the basis of biological experiments and a theoretical study, we have shown that change in the amount of DNA associated with accumulation of cells in G2 enhances radiosensitivity. To demonstrate continuous irradiation with 250 kVp X-rays, we adopted a fractionated regimen of 0.186 or 1.00 Gy per fraction at intervals of 1 h (i.e. 0.186 Gy/h, 1.00 Gy/h on average) to Chinese Hamster Ovary (CHO)-K1 cells. The change in the amount of DNA during irradiation was quantified by flow cytometric analysis with propidium iodide (PI). Concurrently, we attempted a theoretical evaluation of the DNA damage by using a microdosimetric-kinetic (MK) model that was modified to incorporate the change in the amount of DNA. Our experimental results showed that the fraction of the cells in G2/M phase increased by 6.7% with 0.186 Gy/h and by 22.1% with 1.00 Gy/h after the 12th irradiation. The MK model considering the change in amount of DNA during the irradiation exhibited a higher radiosensitivity at a high dose range, which could account for the experimental clonogenic survival. The theoretical results suggest that HRS in the high dose range is associated with an increase in the total amount of DNA during irradiation.