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Precise EBT3 Gafchromic film dosimetry for Grid therapy
摘要： OBJECTIVES: Grid therapy is a radiation therapy technique for the treatment of bulky tumors. The high dose gradients and non-uniformity of dose distributions within the target lead to a challenge in the dosimetry of the Grid radiation fields. The aim of this study is to perform a precise EBT3 Gafchromic film dosimetry for Grid therapy fields using a commercially available ?atbed colour scanner. METHODS: In this project, samples of the EBT3 Gafchromic films are exposed to Grid radiation fields. The irradiated EBT3 ?lms were read using a flatbed Microtek scanner. The responses of these films (i.e. films from the same batch) as functions of the absorbed dose values are calibrated by irradiation under a fixed standard technique (i.e. 10x10 cm2 filed, 100 cm SSD, and depth of the maximum dose). These films are also read with the same scanner using the red, green, and blue channels. Four different approaches were used to evaluate film dosimetry for the Grid therapy applications: 1) single channel film dosimetry method (SCM), 2) dual channel film dosimetry method (DCM), 3) linearized dose-response curve method (LRCM), and 4) triple channel film dosimetry method (TCM). A dose of 20 Gy was delivered to the point along the central axis of the grid hole at the depth of maximum dose (dmax) for a 10 × 10 cm2 Grid field size. Beam profiles and percentage depth dose distributions of the Grid radiation have been measured in water-equivalent phantom material, using EBT3 films. The accuracy of the relative and the absolute dosimetry of the films were examined by comparison of the TLD measured data with the Monte Carlo simulated values. RESULTS: The results of these investigations show that for a gamma index criterion of 5%/3mm, the agreements between the MC calculations dose profiles and the SCM, DCM, LRCM, and TCM film dosimetry approaches the passing rates of 91%, 92%, 95%, and 95%, respectively. A much closer agreement was observed for using a linearized dose-response curve and triple-channel methods. CONCLUSIONS: Selection of an appropriate methodology in Gafchromic film dosimetry may lead to an accurate dose-response in a high dose gradient radiation field such as Grid therapy.
关键词： Gafchoromic film dosimetry,Grid therapy,Monte Carlo simulation
更新于2025-09-11 14:15:04
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Evaluation of Radiation Dose for Dual Energy CBCT Using Multi-Grid Device
摘要： The paper discusses radiation dose of dual energy CT on which copper modulation layer, is mounted in order to improve diagnostic performance of the dual energy CT. The radiation dose is estimated using MCNPX and its results are compared with that of the conventional dual energy CT system. CT X-ray spectra of 80 and 120 kVp, which are usually used for thorax, abdominal, head, and neck CT scans, were generated by the SPEC78 code and were used for the source specification ‘SDEF’ card for MCNPX dose modeling. The copper modulation layer was located 20 cm away from a source covering half of the X-ray window. The radiation dose was measured as changing its thickness from 0.5 to 2.0 mm at intervals of 0.5 mm. Since the MCNPX tally provides only normalized values to a single particle, the dose conversion coefficients of F6 tally for the modulation layer-based dual energy CBCT should be calculated for matching the modeling results into the actual dose. The dose conversion coefficient is 7.2*104 cGy/output that is obtained from dose calibration curve between F6 tally and experimental results in which GAFCHORMIC EBT3 films were exposed by an already known source. Consequently, the dose of the modulation layer-based dual energy cone beam CT is 33～40% less than that of the single energy CT system. On the basis of the results, it is considered that scattered dose produced by the copper modulation layer is very small. It shows that the modulation layer-based dual energy CBCT system can effectively reduce radiation dose, which is the major disadvantage of established dual energy CT.
关键词： Beam hardening effect,Modulation layer,Monte Carlo Simulation,Dual energy cone beam CT,Dose evaluation
更新于2025-09-11 14:15:04
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Analysis of Beam Hardening of Modulation Layers for Dual Energy Cone-beam CT
摘要： Dual energy cone-beam CT can distinguish two materials with different atomic compositions. The principle of dual energy cone-beam CT based on modulation layer is that higher energy spectrum can be acquired at blocked x-ray window. To evaluate the possibility of modulation layer based dual energy cone-beam CT, we analyzed x-ray spectrum for various thicknesses of modulation layers by Monte Carlo simulation. To compare with the results of simulation, the experiment was performed on prototype cone-beam CT for 50～100 kVp with CdTe XR-100T detector. As the result of comparing, the mean energy of energy spectrum for 80 kVp are well matched with that of simulation. The mean energy of energy spectrum for 80 and 120 kVp were increased as 1.67 and 1.52 times by 2.0 mm modulation layer, respectively. We realized that the virtual dual energy x-ray source can be generated by modulation layer.
关键词： Dual energy cone-beam CT,Monte Carlo simulation,Beam hardening effect,Modulation layer
更新于2025-09-11 14:15:04
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Two-dimensional projection Monte Carlo estimators for the study of angular characteristics of polarized radiation
摘要： The paper presents a Monte Carlo algorithm for the study of bidirectional angular characteristics of a scattered polarized radiation based on projection expansion of the density of the corresponding angular distribution over hemispherical harmonics. The results of numerical estimation of two-dimensional angular distributions of the intensity and the polarization degree of the radiation passed through and reflected from optically thick layers of scattering and absorbing substance are presented.
关键词： statistical modelling,radiation transfer,Monte Carlo methods,orthogonal expansion,hemispherical harmonics
更新于2025-09-11 14:15:04
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Performance Analysis of Speckle Filtering on Single-Look Polsar Data for Land Cover Classification
摘要： The speckle ?ltering is an essential preprocessing step of polarimetric SAR (PolSAR) data processing. The PolSAR speckle ?lters perform generally better on multilook datasets. The multilooking is performed to reduce speckle and improve parameter estimation but it also degrades resolution of the datasets. The speckle ?ltering after multilooking further degrades the resolution. The analysis on suitability of speckle ?ltering algorithms for single-look data is absent in the literature. In this paper, state-of-the-art PolSAR speckle ?lters are analyzed for the single-look PolSAR data. The single-look Monte Carlo simulated and real RADARSAT-2 PolSAR data are used for performance analysis.
关键词： SAR,polarimetric,Monte Carlo simulation,?ltering,Speckle
更新于2025-09-10 09:29:36
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Monte Carlo methods for TMD analyses
摘要： Monte Carlo simulations are an indispensable tool in experimental high-energy physics. Indeed, many discoveries rely on realistic modeling of background processes. In the field of transverse-momentum-dependent parton distribution and fragmentation functions there is a clear lack of a reliable Monte Carlo physics generator that can be used in experimental and phenomenological analyses. The need for such Monte Carlo generators, the status of some solutions and prospects are discussed.
关键词： Monte Carlo simulations,fragmentation functions,transverse-momentum-dependent parton distribution,high-energy physics
更新于2025-09-10 09:29:36
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[IEEE 2018 2nd International Conference on Biomedical Engineering (IBIOMED) - Bali, Indonesia (2018.7.24-2018.7.26)] 2018 2nd International Conference on Biomedical Engineering (IBIOMED) - Could Water Replace Muscle Tissue Used in Electron and Photon Beams?: A Monte Carlo Study
摘要： This study was conducted to evaluate the use of different phantom materials (muscle_ICRP, muscle_ICRU, and water) using Geant4-GAMOS Monte Carlo method. GAMOS which based on the Geant4 toolkit developed by European Organization for Nuclear Research (CERN) is a Monte Carlo simulation software. The material composition and density of muscle skeletal (ICRP), muscle striated (ICRU), and water (ICRU) used in this simulation were provided by Geant4 cross section data. Simulation objects consist of world, detector, source, and phantom. The phantom material used was distinguished. The source was placed inside a tube while detector was placed inside phantom. The detector was separated 2 cm from source in +x direction. The photon and electron beam with varied energies 0.5, 1.0, 1.5, and 2.0 MeV was used as source. The simulation time for each simulation was different depend on the incident particle type, particle energy, and phantom material composition. Electron beam takes longer time simulation than photon beam for varied phantom materials. The Rayleigh scattering, Compton scattering, and the photo-electric effect were occurred in each simulation but gamma conversion into electron and positron pairs only discovered in 1.5 and 2.0 MeV photon beam. The positron was produced because of pair production interaction. The energy histogram collected in this simulation shows that the muscle (ICRP and ICRU) material can be replaced by water if the muscle depth from the skin surface is not more than 2 cm. This results also were confirmed by comparing the mass coefficient attenuation and stopping power ratio curves between muscle (ICRP and ICRU) and water material extracted using other Monte Carlo software, EGSnrc.
关键词： stopping power,Monte Carlo,mass attenuation coefficient,Geant4,GAMOS,muscle
更新于2025-09-10 09:29:36
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Dissociating diatomic molecules in ultrafast and intense light
摘要： An ab initio theory is devised for the quantum dynamics of molecules undergoing multiple ionization in ultrafast and intense light. Specifically, the intertwined problem of photoionization, radiative, and electronic transitions in the course of dissociation is addressed which arises, e.g., when molecules are exposed to xuv light or x rays from free electron lasers or attosecond light sources, but the approach is equally useful in optical strong-field physics. The coherent interaction of the molecule with the light in a specific charge state is also treated. I set out from an abstract formulation in terms of the quantum optical notion of system-reservoir interaction using a master equation in Lindblad form and analyze its short-time approximation. First, I express it in a direct sum rigged Hilbert space for an efficient solution with numerical methods for systems of partial differential equations. Second, I derive a treatment via quantum Monte Carlo wave packet (MCWP) propagation. The formalism is concretized to diatomic molecules in Born-Oppenheimer approximation whereby molecular rotation is disregarded. The numerical integration of the master equation is carried out with a suitably factored density matrix that exploits the locality of the Hamiltonian and the Lindblad superoperator with respect to the internuclear distance. The formulation of the MCWP for molecules requires a thorough analysis of the quantum jump process; namely, the dependence on the continuous distance renders a straight wave packet promotion useless and, instead, a projected outer product needs to be employed involving an integrated quantum jump operator.
关键词： Ultrafast and intense light,Born-Oppenheimer approximation,Dissociation of diatomic molecules,Quantum Monte Carlo algorithm,Master equation in Lindblad form
更新于2025-09-10 09:29:36
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Two-dimensional Monte Carlo simulations of coarse-grained poly(3-hexylthiophene) (P3HT) adsorbed on striped substrates
摘要： We investigate the structural phases of single poly(3-hexylthiophene) (P3HT) polymers that are adsorbed on a two-dimensional substrate with a striped pattern. We use a coarse-grained representation of the polymer and sophisticated Monte Carlo techniques such as a parallelized replica exchange scheme and local as well as non-local updates to the polymer’s configuration. From peaks in the canonically derived observables, it is possible to obtain structural phase diagrams for varying substrate parameters. We find that the shape of the stripe pattern has a substantial effect on the obtained configurations of the polymer and can be tailored to promote either more stretched out or more compact configurations. In the compact phases, we observe different structural motifs, such as hairpins, double-hairpins, and interlocking “zipper” states.
关键词： coarse-grained,striped substrates,Monte Carlo simulations,poly(3-hexylthiophene),P3HT,structural phases
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Application of Monte Carlo Method in Uncertainty Analysis of Mismatch Factor
摘要： When calibrating with the direct comparison method, the source reflection coefficient can be calculated by using the scattering parameters of the three-port device, and the mismatch factor and its uncertainty can be calculated by Monte Carlo method (MCM). Moreover, compared to the common method used by calibration laboratories that assuming the mismatch factor as 1, MCM will greatly reduce the uncertainty introduced by mismatch.
关键词： Monte Carlo method,Direct comparison method,Microwave power,Metrology
更新于2025-09-10 09:29:36