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Imaging techniques using protons as incident particles are currently being developed to substitute X-ray computer tomography and nuclear magnetic resonance methods in proton therapy. They deal with relatively thick targets, like the human head or trunk, where protons lose a significant part of their energy, however, they have enough energy to exit the target. The physical quantities important in proton imaging are kinetic energy, angle and coordinates of emerging proton from an absorber material. In recent times, many research groups use the Geant4 toolkit to simulate proton imaging devices. Most of the available publications about validation of Geant4 models are for thin or thick absorbers (Bragg Peak studies), that are not consistent with the contour conditions applied to proton imaging. The main objective of this work is to evaluate the kinetic energy spectrum for protons emerging from homogeneous absorbers slabs comparing it to the experimental results published by Tschalar and Maccabee, in 1970. Different models (standard and detailed) available on Geant4 (version 9.6.p03) are explored taking into account its accuracy and computational performance. This paper presents a validation for protons with incident kinetic energies of 19.68 MeV and 49.10 MeV. The validation results from the emerging protons kinetic energy spectra show that: (i) there are differences between the reference data and the data produced by different processes evoked for transportation and (ii) the validation energies are sensitive to sub-shell processes.

Several total and partial photoionization cross section calculations, based on both theoretical and empirical approaches, are quantitatively evaluated with statistical analyses using a large collection of experimental data retrieved from the literature to identify the state of the art for modeling the photoelectric effect in Monte Carlo particle transport. Some of the examined cross section models are available in general purpose Monte Carlo systems, while others have been implemented and subjected to validation tests for the first time to estimate whether they could improve the accuracy of particle transport codes. The validation process identifies Scofield's 1973 non-relativistic calculations, tabulated in the Evaluated Photon Data Library(EPDL), as the one best reproducing experimental measurements of total cross sections. Specialized total cross section models, some of which derive from more recent calculations, do not provide significant improvements. Scofield's non-relativistic calculations are not surpassed regarding the compatibility with experiment of K and L shell photoionization cross sections either, although in a few test cases Ebel's parameterization produces more accurate results close to absorption edges. Modifications to Biggs and Lighthill's parameterization implemented in Geant4 significantly reduce the accuracy of total cross sections at low energies with respect to its original formulation. The scarcity of suitable experimental data hinders a similar extensive analysis for the simulation of the photoelectron angular distribution, which is limited to a qualitative appraisal., To be published in IEEE Trans. Nucl. Sci

Theoretical and semi-empirical methods to calculate electron impact ionization cross sections for atomic shells are subject to validation tests with respect to a wide collection of experimental measurements to identify the state of the art for Monte Carlo particle transport. The validation process applies rigorous statistical analysis methods. Cross sections based on the EEDL Evaluated Electron Data Library, widely used by Monte Carlo codes, and on calculations by Bote and Salvat, used in the Penelope code, are generally equivalent in compatibility with experiment. Results are also reported for various formulations of the Binary-Encounter-Bethe and Deutsch-Märk models.

A test of Geant4 simulation of electron backscattering recently published in this journal prompted further investigation into the causes of the observed behaviour. An interplay between features of geometry and physics algorithms implemented in Geant4 is found to significantly affect the accuracy of backscattering simulation in some physics configurations. A test of Geant4 simulation of electron backscattering recently published in this journal prompted further investigation into the causes of the observed behaviour. An interplay between features of geometry and physics algorithms implemented in Geant4 is found to significantly affect the accuracy of backscattering simulation in some physics configurations.

Backscattering is a sensitive probe of the accuracy of electron scattering algorithms implemented in Monte Carlo codes. The capability of the Geant4 toolkit to describe realistically the fraction of electrons backscattered from a target volume is extensively and quantitatively evaluated in comparison with experimental data retrieved from the literature. The validation test covers the energy range between approximately 100 eV and 20 MeV, and concerns a wide set of target elements. Multiple and single electron scattering models implemented in Geant4, as well as preassembled selections of physics models distributed within Geant4, are analyzed with statistical methods. The evaluations concern Geant4 versions from 9.1 to 10.1. Significant evolutions are observed over the range of Geant4 versions, not always in the direction of better compatibility with experiment. Goodness-of-fit tests complemented by categorical analysis tests identify a configuration based on Geant4 Urban multiple scattering model in Geant4 version 9.1 and a configuration based on single Coulomb scattering in Geant4 10.0 as the physics options best reproducing experimental data above a few tens of keV. At lower energies only single scattering demonstrates some capability to reproduce data down to a few keV. Recommended preassembled physics configurations appear incapable of describing electron backscattering compatible with experiment. With the support of statistical methods, a correlation is established between the validation of Geant4-based simulation of backscattering and of energy deposition. Backscattering is a sensitive probe of the accuracy of electron scattering algorithms implemented in Monte Carlo codes. The capability of the Geant4 toolkit to describe realistically the fraction of electrons backscattered from a target volume is extensively and quantitatively evaluated in comparison with experimental data retrieved from the literature. The validation test covers the energy range between approximately 100 eV and 20 MeV, and concerns a wide set of target elements. Multiple and single electron scattering models implemented in Geant4, as well as preassembled selections of physics models distributed within Geant4, are analyzed with statistical methods. The evaluations concern Geant4 versions from 9.1 to 10.1. Significant evolutions are observed over the range of Geant4 versions, not always in the direction of better compatibility with experiment. Goodness-of-fit tests complemented by categorical analysis tests identify a configuration based on Geant4 Urban multiple scattering model in Geant4 version 9.1 and a configuration based on single Coulomb scattering in Geant4 10.0 as the physics options best reproducing experimental data above a few tens of keV. At lower energies only single scattering demonstrates some capability to reproduce data down to a few keV. Recommended preassembled physics configurations appear incapable of describing electron backscattering compatible with experiment. With the support of statistical methods, a correlation is established between the validation of Geant4-based simulation of backscattering and of energy deposition.

In this paper are presenting a comparison by using experimental data about chemical damage for all possible physics list for Geant4-DNA (Geant4 version 10.02.p01) for protons incident beam interacting with homogeneous nano-layers of water. Associated to the chemical damage it were evaluated: radial profile of energy deposition, profile of energy deposition on depth, number of interactions, proportion among possible processes and stopping power of the incident particle. The application considers water ultra-thin layers of thicknesses from 2 nm to 200 nm with monodirectional and monochromatic (2 MeV to 20 MeV) protons impinging normally on its entrance surface. It was evoked the standard physics list (“G4EmDNAPhysics” class) and other 5 physics list available (names Opt 1 up to 5). Concerning the experimental data, the films were bombarded by 2 MeV H+ textbf in vacuum at a HVEE 3 MV Tandetron and Xray photoelectron spectroscopy was performed on the irradiated samples at Universite de Namur, Belgium. The preliminary results show that radial and depth profile of energy deposition to all physics lists evaluated presented as expected, with exception for the physics list Opt1. This physics list shows a peak of energy deposition at the end of the layer on depth profile. On radial profile it is clear that the secondaries electrons transported by Opt1 presented larger range than the presented by other evaluated physics list. It was observed for few simulations considering standard physics list that for thickness above $\sim 350$ nm the curve of depth profile achieve it “saturation” and stop the increasing on energy deposition with depth.

The objective of this project was to compare XRMC version 6.5.0–2 to Geant4 version 10.02.p02 and the results of both Monte Carlo tools to experimental data collected by using three different mammographs for dosimetric applications in mammography (external dosimetry), validating XRMC and Geant4 for dosimetric applications in mammography. To validate the quantities simulated one experimental database was structured with data from three different mammographic equipments (Mammomat Inspiration, Mammomat 3000 and LORAD MIII). The absolute quantities exposure and kerma were collected for different setups and used to calculate the derived quantities half-value-layer (HVL) and backscattering (BSF). To evaluate the difference in results due the differences on description of the incident spectra it was modeled spectra from two different sources: catalogue IPEM Report 78 and the spectra generated for Lorad MIII equipment configuration, based on model published by Tucker et al. 1991. The results show good agreement between simulated and experimental data. The XRMC is presenting similar agreement to experimental data as the results presented by Penelope model, but with a significant reduction on running time (in transmission mode it can reduces the running time, at least, $\sim 5$ time compared to Geant4 Penelope model) when normalized values are compared. The use of catalogued spectrum instead of experimental spectrum made visible the need of a semiempirical correction to adjust the number of photons emitted by unit of area by total tube transported charge.

The aim of this work is to simulate transmission data for different beam geometry and material composition in order to evaluate the effect of these parameters on transmission curves. The simulations are focused on outgoing spectra for shielding barriers used in PET facilities. The behavior of the transmission was evaluated as a function of the shielding material composition and thickness using Geant4 Monte Carlo code, version 9.2 p 03.The application was benchmarked for barited mortar and compared to The American Association of Physicists in Medicine (AAPM) data for lead. Their influence on the transmission curves as well the study of the influence of the shielding material composition and beam geometry on the outgoing spectra were performed. Characteristics of transmitted spectra, such as shape, average energy and Half-Value Layer (HVL), were also evaluated. The Geant4 toolkit benchmark for the energy resulting from the positron annihilation phenomena and its application in transmission curves description shown good agreement between data published by American Association on Physicists in Medicine task group 108 and experimental data published by Brasil. The transmission properties for different material compositions were also studied and have shown low dependency with the considered thicknesses. The broad and narrow beams configuration presented significant differences on the result. The fitting parameter for determining the transmission curves equations, according to Archer model is presented for different material. As conclusion were defined that beam geometry has significant influence and the composition has low influence on transmission curves for shielding design for the range of energy applied to PET.

Evolutions of Geant4 code have affected the simulation of electron backscattering with respect to previously published results. Their effects are quantified by analyzing the compatibility of the simulated electron backscattering fraction with a large collection of experimental data for a wide set of physics configuration options available in Geant4. Special emphasis is placed on two electron scattering implementations first released in Geant4 version 10.2: the Goudsmit-Saunderson multiple scattering model and a single Coulomb scattering model based on Mott cross section calculation. The new Goudsmit-Saunderson multiple scattering model appears to perform equally or less accurately than the model implemented in previous Geant4 versions, depending on the electron energy. The new Coulomb scattering model was flawed from a physics point of view, but computationally fast in Geant4 version 10.2; the physics correction released in Geant4 version 10.2p01 severely degrades its computational performance. Evolutions in the Geant4 geometry domain have addressed physics problems observed in electron backscattering simulation in previous publications., To be published in IEEE Trans. Nucl. Sci

Half Value Layer (HVL) test is an important technical information in conventional radiology once it is the only test which allows us to quantify beam quality in a complete way. This work promotes a preliminary analysis of the impact of aluminum alloy composition in the determination of HVL value taking into account a realistic geometry. Deterministic calculations and Monte Carlo Method were applied in order to make the proposed analysis. Six aluminum alloys (99% pure) commercialized and pure aluminum were used as comparative basis for both methods. Experimental data were collected in conventional radiology, using tungsten target and aluminum filter for two peak tensions (66 kVp, 81 kVp), and in mammography, using three target filter combinations( molybdenum-molybdenum, molybdenum-rhodium, tungsten-rhodium) for three peak tensions (25 kVp, 30 kVp and 35 kVp). Spectra used in the deterministic calculations were taken from Report No 78 of Institute of Physics and Engineering in Medicine, 1997. Results show that Mammography is more sensitive than conventional X-ray equipment to impurities in aluminum alloys (up to 34.65% variation for W-Rh combination with 30 kVp).

Imaging techniques using protons are actively being developed currently to substitute X-ray computer tomography and nuclear magnetic resonance method in proton therapy. They deals with relatively thick targets like the human head or trunk where protons lose the major part of their energy, however they having enough energy to exit the target. The physical quantities important in proton imaging are proton exit energy, angle and coordinates. Nowadays many research groups are using The Geant4 toolkit for the development of proton imaging devices. However the most of available publications about validation of the Geant4 models are or for thin absorbers, or for energy deposition of completely absorbed protons (Bragg Peak), what are not important characteristics in proton imaging. The main objective of this work is to validate different models available on Geant4 (version 9.6.p03) taking into account its accuracy and computational performance from the viewpoint of proton imaging. This paper presents the comparison against experimental data published by Tschalar and Maccabee (for incident kinetic energies for protons of 19.68 MeV and 49.10 MeV). The results show that for the validation energies the spectra of the kinetic energy of the emerging protons: (i) there are differences between the validation and the different processes invoked for transportation and (ii) the validation energies are sensitive to sub-shell processes.

Several models for the Monte Carlo simulation of Compton scattering on electrons are quantitatively evaluated with respect to a large collection of experimental data retrieved from the literature. Some of these models are currently implemented in general purpose Monte Carlo systems; some have been implemented and evaluated for possible use in Monte Carlo particle transport for the first time in this study. Here we present first and preliminary results concerning total and differential Compton scattering cross sections., Comment: 5 pages, 3 figures, to be published in the Proceedings of IEEE Nuclear Science Symposium 2013

Several physics methods for the simulation of the photoelectric effect are quantitatively evaluated with respect to a large collection of experimental data retrieved from the literature. They include theoretical and empirical calculations of total and partial cross sections, and calculations of the photoelectron angular distribution. Some of these models are currently implemented in general purpose Monte Carlo systems; some have been implemented and evaluated for possible use in Monte Carlo particle transport for the first time in this study., Comment: To be published in the Proceedings of IEEE Nuclear Science Symposium 2013

A comprehensive analysis of the effects of Geant4 algorithms for condensed transport in detectors is in progress. The first phase of the project focuses on electron multiple scattering, and studies two related observables: the longitudinal pattern of energy deposition in various materials, and the fraction of backscattered particles. The quality of the simulation is evaluated through comparison with high precision experimental measurements; several versions of Geant4 are analyzed to provide an extensive overview of the evolution of Geant4 multiple scattering algorithms and of their contribution to simulation accuracy., Comment: To be published in the Proc. of CHEP (Computing in High Energy Physics) 2012

Different authors publish about the transmission curves as a function of shielding material thickness. It is important to define these curves of transmission of photons using the material composition available and regularly commercialized. So the objective of this work was to simulate the transmission data and to generate the transmission curves as function of different material composition as function of the thickness to the spectrum energy used on PetCT. That way we simulate an incoming monoenergetic photons beam of 511 keV. Were collected in sensitive volume the absorbed energy and the photon flux on spherical sensitive volume with a radius of 1.0cm composed of air. We simulated two sensitive volumes one before and one after the shielding wall. We simulate shielding wall made of: lead; concrete, described according Simpkin and ICRU 44 documentation; iron alloy composed by 1% of carbon and barite mortar. The curves of transmission were compared to other simulated data and to real data. As results we generate a group of data and fitting curves applied to the medical application getting concordance to the previously published data and the real data collected. We generated curves of transmission data for barite mortar, undefined for these applications until now.

The aim of this work is to compare the dosimetric data and the photon fluency in three positions among different homogeneous models to a voxel model. Were simulated the mammographic dosimetric homogeneous models and a breast voxel model which represents 4.0 cm compressed woman breast, with 50% of glandular tissue. Were simulated the photon spectra of Mo-30Mo from 26 kVp up to 34 kVp; and Mo-25Rh from 26 kVp up to 34 kVp characterized by the HVL values. For all techniques simulated the normalized glandular dose was superestimated by the BR12 homogeneous models and underestimated by PMMA homogeneous models comparing to voxel model. Among the models studied was the model proposed by Dance that presented a behavior similar to voxel model, however it underestimates all the D gN .

Purpose: To compare conversion coefficient of KERMA free in air to glandular dose, in mammography, simulated to BR12 model and a realistic breast voxel model. Method and Materials: We simulate the glandular dose (Dg) and KERMA free in air (Kai), using the Monte Carlo program MCNP (version 4B) to estimate the conversion coefficient (cg) of KERMA free in air at entrance skin in glandular dose. The computational universe generated to simulate a mammographic procedure mimics LORAD III mammographic equipment. The focal spot of molybdenum irradiates photons isotropically in a solid angle of 16.8°. The bucky is 0.6190 m far from de focal spot. Above the model there is a PMMA compress paddle 0.002 m thicker. The add filtration (30 μm Mo thicker and 25 μm Rh thicker) was located at 0.050 m far from the focal spot. Tow spectra were used in voxel model simulations: 28 kVp with Mo add filtration and 30 kVp with Rh add filtration. Results: The cg presented on Mo/Rh simulation was 1.5 times larger than the presented on Mo/Mo simulation. Comparing the voxel model to the BR12 model we have actually a super estimation on both simulated cg values: 3.4 times considering the simulation with Mo/Mo target/filter combination, and 2.4 times considering the simulation with Mo/Rh target/filter combination. Conclusion: The cg values show a decrease of 58.7% considering the Mo/Rh target/filter combination and a decrease of 70.2% considering the Mo/Mo target/filter combination, to the realistic breast model as comparative pattern. These variation on cg are probably caused by the definition of a non‐anthropomorphic model composed by an homogeneous distribution of tissues as pattern, that makes unviable the observation of the absorbed energy by each tissue; and because this model do not consider the position of glandular tissue in the real breast geometry.