This article presents an overview of current experiments and calculations on research of new method of radiation therapy – flash radiotherapy. This method implies an increase of the average dose rate by 40 Gy/s and more, thus providing better sparing of normal tissue compared to conventional radiotherapy. The article analyzes the results of recent experiments on flash radiotherapy with proton beams, electrons and braking radiation. It also describes technical problems for achieving high dose rates and the possible ways to solve them. Flash radiotherapy method on different particles appears to be promising and probably it will be applied in the future. However, many questions remain unclear in order to actively use this method for the treatment of patients.
Show AbstractThis study seeks to calculate the conversion coefficients from fluence to local skin absorbed dose (LSD/Φ) for monoenergetic electrons and positrons from 0.01 to 10 MeV. The conversion coefficients calculation used a new analytical approach. The obtained results are in good agreement with those previous published. A new analytical fit has provided a convenient approach for determining conversion coefficients for discrete incidents.
Show AbstractScreening mammography is the examination of reference in the fight against breast cancer because of its sensitivity in detecting microlesions. Thus, it is crucial to ensure a good quality examination with the most suitable dose, requirements will depend on the choice of exposure parameters (anode/filter, tube voltage and current) and the acquisition procedures. To optimize practices, we must understand the relationship between breast dose and image quality. This can be reached by knowing the X-ray energy spectra. This study aims to generate spectra of a mammographic x-ray tube, using two types of targets, Mo and Rh by MONTE CARLO simulation using Gate code (GEANT4). To predict the X-ray spectra for the Mo/Mo and Rh/Rh target/filter combinations of the screening mammography tube, Monte Carlo modeling has been carried out using the GATE code (GEANT4); the generated spectra were validated by comparing them with those of the IPEM report 78. The curves of the spectra obtained by the Monte Carlo simulation have been normalized for a reliable comparison. The evaluation of these curves has been performed using a statistical analysis with the student’s t-test. The results show that the energy spectra of the GATE code are in agreement with those produced by the IPEM 78 report, no statistically significant differences have been observed between the IPEM and simulated spectra (p<.05), even though there are slight differences between them, especially in the characteristic intensity of the K-beam and in the low-energy range. Monte Carlo simulation is a reliable method for generating mammography spectra and can be used as a tool for optimizing acquisition parameters.
Show AbstractThe objective of this study is to demonstrate by Monte Carlo simulation the variation of the surface dose and dose rate for the 6MV-FFF mode compared to the 6MV-FF mode. We demonstrate the effect of the filter on the capture of low energy photons and their impact on the surface dose and dose rate as well as the contribution of the dose induced by the contamination particles. Furthermore, the effect of the heterogeneous medium on the dose rate. The Monte Carlo simulations were validated by experimental measurements in a water phantom using the gamma index (2%/2 mm) and the mean absolute error (MAE). The results obtained indicate that the surface dose is increased in the FFF mode by almost 10% in the 3×3 cm2, 5×5 cm2 and 10×10 cm2 irradiation fields. The dose rate (Gy/primary particle) is increased for the 6MV-FFF mode by a factor of almost 2.5.
Show AbstractGiven the lack of data on radiation shielding properties of iron oxide (magnetite) against gamma-rays, this study addresses radiation shielding characteristics of a novel lead-free material, namely magnetite/high density polyethylene (HDPE/Fe3O4) nanocomposite for diagnostic radiology and nuclear medicine purposes. Thus, radiation shielding characteristics of this nanocomposite, including mass attenuation coefficients, half-value layer (HVL) and transmittance (I/I0%) values at various concentrations namely 0, 1.16, 1.93, 3.87, 5.8, and 7.74 w% were obtained via the MCNPX code at low and medium energies. The simulation results exhibited a good agreement with the other approaches namely XCOM and XMuDat programs. Besides, the effective atomic number was calculated using direct-method and Auto-Zeff software. The results showed that with an increase in the magnetite w%, the mass attenuation coefficients underwent an increasing trend followed by the effective atomic number.
Show AbstractThe determination of the dose distribution is the key step for accurate dose delivery in brachytherapy as well as radiotherapy application. This research study contributes on the characterization of the 60Co high dose rate brachytherapy source model Co0.A86. We followed the recommendations of the American Association of Physicists in Medicine (AAPM) and European Society for Radiotherapy and Oncology (ESTRO) on dose calculation. In addition, this study aims also to investigate the accuracy of TG-43 algorithms dose calculations in different mediums relevant to high dose rate brachytherapy. For algorithm implementation, we have used the GEANT4 Application for Emission Tomography Monte Carlo code to reach our goal. Furthermore, we compared the obtained results with the previous published results. The obtained dosimetric data sets are in good agreement with the quoted values in the previous studies, where the authors used different Monte Carlo codes.
Show AbstractIn this study, the objective was to give more data related to the use of GATE (Geant4-based Application for Tomographic Emission) and Al 2 O 3:C Optically Stimulated Luminescence (OSL) nanodots, as two alternative methods to estimate entrance surface dose (ESD) in mammography. First, ESD values were simulated with GATE and compared with values measured with Al 2 O 3:C OSL nanodots and Solid State kV/Dose Multisensor AGMS-M+ (Radcal,USA), using a standard breast phantom MTM100 (CIRS, USA). On the other hand, GATE simulations were also performed with PMMA slabs of different thicknesses (10 to 90 mm) and then compared with experimental values using AGMS-M+ detector. Results pointed to a maximum difference of 17%, between X-ray spectra simulated with GATE and those calculated with the IPEM report number 78 software, for this reason, the air kerma factor was calculated with GATE and IPEM and compared to the one measured by the AGMS-M+ detector. The ESD results indicate that GATE and Al 2 O 3:C OSL nanodots values were compatible within 4% with those obtained with AGMS-M+. This work gives more data according to the use of GATE and Al 2 O 3:C OSL nanodots to determine the ESD. Indeed, in the literature, there are few studies related to the use of GATE code and Al 2 O 3:C OSL nanodots in mammography systems.
Show AbstractThis work aims to optimize the scanning parameters of Chest and Abdomen protocols in Computed Tomography, whilst maintaining image quality and reducing dose. Two phantoms have been used to evaluate the dose and image quality on a 16-slice HITACHI CT system by establishing the optimization threshold for each protocol. The proposed Thoracic protocol has shown a reduction in Computed Tomography Dose index (CTDIvol) and Contrast-Noise Ratio (CNR), and the spatial resolution has remained stable with a slight increase in noise. For the optimized Abdominal protocol, CTDIvol has reduced significantly, noise has increased at the two new proposed energies of 100KV and 120KV, and CNR has decreased. This research has shown that by optimizing Chest and Abdomen protocols, substantial dose reductions may be achieved without compromising image quality when using a multi-slice Scanner.
Show AbstractBackground: Screening mammography is an unavoidable method for detecting breast cancer. It is therefore imperative to ensure a quality examination. To optimize practices, it is necessary to control the relationship between the dose to the breast and the image quality. This can be achieved by the Average Glandular Dose (AGD). The objective of this study is to calculate the average absorbed breast dose during a mammography examination by MONTE CARLO simulation using the GATE code (GEANT4). Methods: In this study, we performed our modulation on a digital mammography screening machine. The validation of the modelled simulation configuration was obtained by comparing the modulated spectra with the spectra produced by IPEM SRS 78, and by calculating the HVL values in Al. Finally, the values of the average absorbed dose were studied using the Monte Carlo code GATE, the results were compared with the experimental measurements using a semiconductor detector (Radcal AGMS -DM+) and a MTM100 phantom. Result: Our calculated results for the average glandular dose were consistent with the results of the experimental measurement and the energy spectra produced by GATE were in good agreement with that produced by IPEM Report 78. Conclusion: It can be assumed that the dose received in Mammography is highly dependent on the energy spectrum of the beam. Our modeling for screening mammography using GATE can be applied to further dosimetric studies of the mammography radiation exposure to the breast.
Show AbstractThe use of Monte Carlo methods can help measure radiation doses during a CT procedure to assess risk. Before any Monte Carlo-based simulation can be performed, it must be validated first. This study presents a validation of a Monte Carlo simulation to estimate the CTDI using a Hitachi Supria 16-slice scanner. This simulation was performed using GATE software which is based on GEANT4 code. CTDI is the dose delivered by a CT scanner from a single gantry rotation. It serves as a means of determining the absorbed dose during a CT examination. The objective of this study was the validation of a CTDI computed by Monte Carlo simulation with data from experimental measurements for a 16-slice CT system. An ionization chamber and its associated electrometer were used for phantom measurements. The cylindrical phantom of polymethylmethacrylate (PMMA) with a diameter of 16 cm was used for the determination of the CTDI for 80, 100, and 120 KVp at 100 mAs. The CTDI was measured at the center (CTDIc) and at four locations on the periphery (CTDIp) of the phantom using the pencil chamber, and then the CTDIw was determined. The measurement data are compared with the results of the GATE simulation. GATE is a simplified platform of the GEANT4 code which is based on Monte Carlo techniques. The differences between CTDI measurements and simulations are 11%, 9%, and 17% for 80, 100, and 120 KVp respectively. There is a good agreement of CTDIw between simulated and measured results. Thus, the evaluation of CTDIw during a CT protocol can be performed using the configuration adopted in this study.
Show AbstractThe GEANT4 software package was used to simulate the passage of fast electron beams through a fragment of bone tissue during radiation sterilization. Data on the spatial distribution of the absorbed dose in a sample with the characteristics of bone tissue, depending on the determining conditions of the radiation treatment process, have been obtained and analyzed, which make it possible to develop practical recommendations for optimizing the process of radiation sterilization of bone implants with a flow of fast electrons.
Show AbstractTo improve the irradiation accuracy in hadrontherapy, a lot of studies are in the evaluation uncluding how to integrate MRI and PET at the treatement of cancer patients. These two future techniques will offer simultaneously the monitoring of the beam during the irradiation. In this study and for the first time, we calculated the dose distribution in a volume of the head for several carbon ion energies and at different values of the magnetic field B using fluka MC code. Afterwards, either longitudinal or radial dose deflection was simulated with and without B. The maximum longitudinal deviation of bragg pick depth was 0.672 mm at 200 MeV and the the maximum radial deflection was almost 4.23 cm at 100 MeV. Both of them are in the presence of B=1.5T. Our results are in a good agreement with previous experimental results (a maximum relative error founded of 2.08%). The results of this study will offer the monitoring of the dose deposition with good accuracy in the presence of a magnetic field in carbon ion therapy.
Show AbstractSpin asymmetries in elastic lepton-deuteron scattering in the one-photon-exchange approximation within the limit of zero lepton mass are investigated. Numerical estimations for the spin asymmetries $A^{(0)}_{xx}$, $A^{(0)}_{xz}$, and $A^{(0)}_{zz}$ caused by an unpolarized lepton beam and a tensor polarized deuteron target are presented. The estimated results are analyzed at different lepton beam energies and scattering angles. In addition, the influence of the obtained results on the nucleon structure is investigated for the first time. We found a considerable dependence of the results on the nucleon structure at lepton scattering angles greater than 30$^\circ$, particularly in the case of $A^{(0)}_{zz}$ asymmetry. The estimated results are of particular interest due to the planned experimental measurements of lepton-deuteron scattering which aim for accurate calculation of the charge radius of the proton to a high degree of precision.
Show AbstractThis study presents a method of increasing the uniformity of the dose absorbed by a simulated parallelepiped shaped object irradiated with accelerated electrons with the energy ranging from 4 to 10 MeV. The method uses aluminum plates to modify the electron energy spectrum in order to increase the dose uniformity by 15-20 %.
Show AbstractIn this work the effect of mass model choice, used in astrophysical reaction rate statistical model calculation of neutron capture, on the results of r-process nucleosynthesis simulation is studied. Four mass models are observed: micro-macroscopic models FRDM, HFB-24, WS+RBF and local mass relations model LMR. Significant impact of nuclear mass variations on the cross sections and rates of radiative neutron capture are shown. Using observed mass models data bases in the REACLIB format were created, that were used to calculate r-process yields in the standard conditions. LMR model usage lead to significant increase of heavy nuclei yields in the region of mass numbers 170 ≤ A ≤ 190.
Show AbstractThe consequences of radiological accidents outside the nuclear sector can be fatal. Therefore, emergency response plans must take into consideration the worst scenarios. This article presents a simulation of an accident in which it was assumed that the assembly of cobalt-60 sources from the irradiator installed at National Institute of Agronomic Research (NIAR) of Tangier was found on the ground. The Monte Carlo GEANT4 code was used to estimate the equivalent dose rate in the organs of an individual presented by an anthropomorphic phantom at dierent distances, and its variance with decreasing activity, this simulation will allow as to make the best decisions, correct actions, prevent serious radiobiological damage and to prepare the best methods of intervention in the occurrence of this scenario.
Show AbstractWe study theoretically the harmonic generation in planar and elliptic undulators of free electron lasers. The study is conducted both analytically and numerically. The radiation of the second harmonic is explored in details for the planar undulator of FEL LEUTL, while for the KAERI elliptic undulator with the third field harmonic, its fifth harmonic radiation is also in focus of our study. The analytical and numerical results are compared with each other and with the available data. The radiation of a FEL with each of these undulators is modeled for the same beam and the harmonic generation in such FEL with elliptic and planar undulators is explored. The results are compared with the experimental data of the LEUTL FEL. The effects of the beam divergence, beam section and alignment, energy spread, diffraction and that of the undulator parameter k on the even and odd harmonic generation are separated from each other analytically and elucidated individually. Our results for the LEUTL FEL are compared with predictions of the theoretical approaches of other authors and with the measured data for the harmonic generation at LEUTL.
Show AbstractThe computational complexity of the used method is an important parameter in the fiber-optic communication lines practical design, since the speed and energy efficiency of the receiving device directly depend on this parameter. From an engineering point of view, the computational cost of the used methods should be comparable with one of linear equalizer, which computational complexity is $ \Theta (N \log_2 N) $ operations, where $ N $ is the grid size by time. The subject of this work is a generalization of the superfast ($ \Theta (N \log_2 ^ 2 N) $ arithmetic operations) methods LayerPeeling and InverseLayerPeeling, developed for the nonlinear Schrödinger equation, to the Manakov system.
Show AbstractThe absorption and luminescence spectra and the luminescence decay kinetics of uranyl ions (UO22+) in the presence of organic reagents based on 2,2'-bipyridyldicarboxamides with various substituents have been studied. The quantum yields and luminescence lifetimes of uranyl nitrate hexahydrate and uranyl complexes with organic ligands in acetonitrile solutions have been determined. The mechanism of energy transfer in uranyl complexes is proposed.
Show AbstractThe article discusses the problem of analyzing the Raman spectra of carbon nanotubes and establishing a relationship between the observed features and the distribution of structural defects. Based on examples of the obtained spectra of multi-walled carbon nanotubes, a complex graphic representation of their spectral features is presented and the fundamental aspects of their interpretation are considered. The possibility of comparing the structure of various samples of a given nanomaterial using Raman spectroscopy is shown.
Show AbstractThis work demonstrates the usage of polarization analysis of reflected radiation to reveal the contributions from magnetically ordered phases in poorly resolved Mössbauer spectra obtained with π-polarized radiation from the Synchrotron Mössbauer Source. The study was carried out for the cluster-layered structure [57Fe (0.08 nm) / Cr (1.08 nm)]30. As a result it was shown that only 16% of iron atoms are ferromagnetically ordered, the rest of the iron atoms are in spin glass state.
Show AbstractThe structure of charged interfacial boundaries of mechanically updated Sn and Pb electrodes with LiClO4 solutions in acetonitrile (AN) of different concentrations was studied using the impedance method and cyclic voltammetry. The potential intervals in which these electrodes can be considered as ideally polarized in a good approximation are established. The zero charge potentials were determined, which were: -0.37 and -0.59 V (relative to us. water efficiency) for Sn and Pb electrodes, respectively. It is shown that the experimental dependences of the capacity on the potential are in good agreement with the classical Gui-Chapman-Stern-Graham model. The correlations of the differences in the experimental values of the potentials at zero and significant negative charges of the double electric layer with the difference in the values of the electron output into vacuum for these metals are considered and analyzed. The results obtained in AN solutions are compared with the data in aqueous solutions of surface-inactive electrolytes. It is shown that by the nature of the interaction of Sn and Pb electrodes with AN and H2O molecules, these metals should be attributed to lyophobic systems similar to mercury and a number of other mercury-like sp-metals
Show AbstractIn this work, we present a novel program LOIS (Low Orbit Improvement Software) for precise orbit determination of Low Earth orbit (LEO) satellites based on Global navigation satellite system tracking data (GNSS). Moreover, we discuss theoretical background of two orbit improvement methods and GNSS data processing. We modeled different orbits to check the orbit determination solution and proved the effectiveness of our user-friendly software.
Show AbstractThe time distributions of particles in extensive air showers (EASs) have been studied using the EAS array at Moscow State University [1, 2]. More than $10^{5}$ particles are produced in an EAS during the interaction of cosmic rays with energies above $10^{14}$~eV with the atmosphere. Delayed particles are detected in 3.5\% of EASs with an unshielded detector located at the Earth’s surface. Muons are detected in 60\% of EASs using a shielded detector located under a soil ground layer equivalent to a 20 m of water column. The detector signals are recorded using a two-beam analog storage oscilloscope. It has been found that the detection probability increases when observing muons for EASs containing from $10^{5}$ to $10^{6}$ particles, and when observing delayed particles for EASs containing from $10^{6}$ to $10^{7}$ particles. The distribution over distances to the EAS axis when observing delayed particles is wider than for muons and the age distributions do not differ within errors. The features of EASs with delayed particles and the hypothesis that the height of the appearance of delayed particles can be higher than the height at which EAS electrons and muons are produced are considered.
Show AbstractThe principles and technical requirements of the classical Michelson interferometer as a distance meter in a space satellite cluster for measuring the parameters of the Earth's gravitational field are considered.
Show AbstractA physical analysis of the generation of tsunami waves by seismic movements of the ocean floor is presented. For a set of strong underwater earthquakes, the work done against hydrostatic pressure during coseismic displacements of the ocean floor and the available potential energy, tsunami energy, are estimated. It is shown that an insignificant part of the earthquake energy (from 0.004% for Mw = 7 to 0.16% for Mw = 9) is transferred to the tsunami waves, while the work done against the hydrostatic pressure is comparable in absolute value to the earthquake energy estimated by the Kanamori formula.
Show AbstractThe effects of wind on the thermal bar behavior during autumn cooling of a body of water were studied on an example of Kamloops Lake (Canada) using numerical modeling. This paper focuses on the winds with various speed, blowing opposite to the direction of the thermal bar propagation: calm (0.1 m/s), light air (1 m/s), light breeze (2 m/s), gentle breeze (4 m/s), moderate breeze (6 m/s), fresh breeze (9 m/s), and strong breeze (12 m/s). The influence of wind force on the timing of the formation of an autumnal thermal bar, dynamics of its movement and specific nature of subsurface currents is found.
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