PURPOSE:In IOERT breast treatments, a shielding disk is frequently used to protect the underlying healthy structures. The disk is usually composed of two materials, a low-Z material intended to be oriented towards the beam and a high-Z material. As tissues are repositioned around the shield before treatment, the disk is no longer visible and its correct alignment with respect to the beam is guaranteed. This paper studies the dosimetric characteristics of four possible clinical positioning scenarios of the shielding disk. A new alignment method for the shielding disk in the beam is introduced. Finally, it suggests a new design for the shielding disk.METHODS:As the first step, the IOERT machine "Mobetron 1000" was modeled by using Monte Carlo simulation, tuning the MC model until an excellent match with the measured PDDs and profiles was achieved. Four possible shielding disk positioning scenarios were considered, determining the dosimetric impact. Furthermore, in our center, to prevent beam misalignment, we have developed a shielding disk equipped with guiding rods. Having ascertained a correct alignment between the disk and the beam, we can propose a new internal design of the shielding disk that can improve the dose distribution with a better coverage of the treated area.RESULTS:All MC simulations were performed with a 12 MeV beam, the maximum energy of Mobetron 1000 and a 5.5 cm diameter flat tip applicator, this applicator being the most clinically used. The simulations were compared with measurements performed in a water phantom and showed good results within 2.2% of root mean square difference (RMSD). The misplacement positions of the shielding disk have dosimetric impacts in the treatment volume and a small translation could have a significant influence on healthy tissues. The D-scenario is the worst which could happens when the shielding disk is flipped upside down, giving up to 144% dose instead of 90% at the surface of the Pb/Al shielding disk. A new shielding design used, together with our alignment tool, is able to give a more homogeneous dose in the target area.CONCLUSIONS:The accuracy of shielding disk position can still be problematic in IOERT dosimetry. Any method that can ascertain the good alignment between the shielding disk and the beam is beneficial for the dose distribution and is a prerequisite for an optimized shield internal design that could improve the coverage of the treated area and the protection of healthy tissues.

dict the delivered absorbed dose distribution, allowing comparison with the TPS.EPID images were taken during 6MV treatment delivery, with a dose rate of 600 MU/min, from aSi1000 EPID (Varian).Mounted with Exact-arm on a Clinac 23iX equipped with a multi-leaf collimator (120 leaves).The EPID were acquired using the half-resolution mode.2D plane images were calculated in Eclipse TM at the maximum depth dose in a water phantom.Results.Learning was performed using 11 input/output datasets from IMRT treatments.All of the used datasets (both EPID inputs and absorbed dose distribution outputs) consisted of 384 Â 512 pixels.Learning can be time consuming but once the ANN has been fixed, its use during the recognition phase will be instantaneous.The gamma index, c, was used to evaluate the difference between the ANN calculated and planned distributions.c gives the number of pixels (as a percentage) that respect a given objective.c (2% , 2 mm) for Head and Neck cancers was found to be 99.7%, highlighting the ANN capability to predict the absorbed dose distribution based on EPIDs.Conclusions.It was shown that patient-specific quality assurance of IMRT based on EPID can be performed with neural networks algorithms.Next work would be extending algorithms for in vivo dosimetry purpose.

The performance of the energy degrader in terms of beam properties directly impacts the design and cost of cyclotron-based proton therapy centers. The aim of this study is to evaluate the performances of different existing and novel degrader materials. The quantitative estimate is based on detailed GEANT4 simulations that analyze the beam-matter interaction and provide a determination of the beam emittance increase and transmission. Comparisons between existing (aluminum, graphite, beryllium) and novel (boron carbide and diamond) degrader materials are provided and evaluated against semi-analytical models of multiple Coulomb scattering. The results showing a potential in emittance reduction for novel materials are presented and discussed in detail.

This paper describes a multi-scale approach for the modelling of the degradation of model cement pastes using reactive transport. It specifically aims at incorporating chemistry-transport feedback results from a pore-scale approach into a continuum description. Starting from a numerical representative elementary volume of the model cement paste, which was built according to extensive experimental dedicated chacarterizations, this paper provides three separate descriptions of two different degradations: leaching and carbonation. First, 2D pore-scale simulations are performed and predict degradation depths in very good agreement with experiments. Second, 3D pore scale descriptions of how the microstructre evolves provides accurate description of the evolution of transport properties through degradation. Finally, those latter results are incorporated as a feedback law between porosity and effective diffusion coefficient into a 1D continuum approach of reactive transport. This paper provides pore-scale explanations of why reactive transport modelling has encountered mitigated success when applied to cementitious materials, especially during carbonation or degradations consisting of precipitation reactions. In addition to that, different degradation modellings are in very good agreement with experimental observations.

The activation of concrete is a real problem from the point of view of waste management. Because of the complexity of the issue, Monte Carlo (MC) codes have become an essential tool to its study. But various codes or even nuclear models exist in MC. MCNPX and PHITS have already been validated for shielding studies but GEANT4 is also a suitable solution. In these codes, different models can be considered for a concrete activation study. The Bertini model is not the best model for spallation while BIC and INCL model agrees well with previous results in literature.

Cementitious materials are widely used in the concepts of radioactive waste disposal facilities. During the lifetime of these disposals, those materials will undergo physicochemical degradations. To assess their impacts, reactive transport modelling is used. Reactive transport codes modify the transport properties based on the modelled porosity evolution by using Archie's law as a feedback between porosity and diffusive properties. These laws are not suited to cementitious materials, whose pore structure is complex and expands over a wide range of pore sizes. The ultimate goal of this research is about developing a microstructure-based feedback relation for the diffusive properties of complex porous structures such as cementitious ones. Therefore, we developed an algorithm designed to generate numerical microstructures representative of simplified cement pastes and performed an experimental campaign consisting of dedicated experiments. A random-walk algorithm is used to compute the effective diffusion coefficients of our numerical microstructures. This paper investigates the description of the initial numerical microstructure and how transport properties are sensitive to different microstructural features that can be controlled from the designed algorithm. Simulations both on the experimental microtomograph and the generated microstructures allow to show that our models are complete to describe the microstructure and diffusion transport property of simplified cementitious materials. Sensitivity analysis is also provided, whose results show that a simple feedback relation cannot properly describe these transport properties. This gives confidence in our approach and its future extension toward the description of cementitious material degradations.

We define the interface excitation parameter (IEP) as the change in excitation probability, caused by the presence of a medium‐medium interface crossed by an electron, in comparison with an electron for which only bulk excitations are considered. This definition is established by analogy with the definition of the surface excitation parameter for which one of the two media of the interface is the vacuum and which has already been extensively studied. To calculate the IEP (as well as the energy‐differential IEP or DIEP), we generalize the model developed by Tung, Chen, Kwei and Chou [C. J. Tung, Y. F. Chen, C. M. Kwei and T. L. Chou, Phys. Rev. B 49 (1994) 16684] from dielectric response theory for surface excitation parameter determination. We perform these calculations for angles between 0 o and 60 o , for electron energies between 200 and 3000eV and for various combinations of materials, chosen for their academic (as Al/In) or practical interest (as SiO 2 /Si for instance). We show that for materials with “similar” dielectric properties (metal/metal), the IEP is completely negligible. On the contrary when the materials of the interface are characterized by a large energy band gap difference, as metal/insulator or semiconductor/insulator, the IEP can reach a value of about 0.26 for the smallest electron energies considered here. Moreover, we show that for the SiO 2 /Si interface, the energy‐differential IEP obtained from our model is in good agreement with previous experimental data. Copyright © 2015 John Wiley & Sons, Ltd.

Inside an IBA proton therapy centre, secondary neutrons are produced due to nuclear interactions of the proton beam with matter mainly inside the cyclotron, the beam line, the treatment nozzle and the patient. Accurate measurements of the neutron ambient dose equivalent H*(10) in such a facility require the use of a detector that has a good sensitivity for neutrons ranging from thermal energies up to 230 MeV, such as for instance the WENDI-2 detector. WENDI-2 measurements have been performed at the Westdeutsches Protonentherapiezentrum Essen, at several positions around the cyclotron room and around a gantry treatment room operated in two different beam delivery modes: Pencil Beam Scanning and Double Scattering. These measurements are compared with Monte Carlo simulation results for the neutron H*(10) obtained with MCNPX 2.5.0 and GEANT4 9.6.

Monte Carlo codes have become an essential tool for studying the radiation protection of particle accelerator facilities such as a proton therapy center.The MCNPX code is well adapted for shielding study but the GEANT4 toolkit is also a suitable solution.Benchmark simulationssecondary-particle production and attenuationand shielding calculations for a proton therapy center show that both codes provide results in good agreement.

The energy loss function (ELF) is a key parameter for the calculations of energy losses undergone by electrons in matter. It is often the only input in the calculations performed within the models based on the semi‐classical dielectric response theory. Its perfect knowledge is thus of primordial importance. To evaluate the ELF, it is usual to consider as a model an expansion in Drude–Lindhard (DL) type oscillators with fixed values of the strength, width, energy and dispersion for the various oscillators. However, for materials that are characterized by a single sharp oscillator as aluminium or indium, it has been shown [Phys. Rev. B 46 (1992) 2486] that the damping parameter that corresponds in the DL model to the width of the oscillator increases for decreasing incident electron energy. To emphasize this effect, we perform in this work systematic calculation of the ELF for an indium target and for incident electron energies between 200 and 2000 eV. The ELF is determined by comparing REELS (reflection electron energy loss spectroscopy) experimental inelastic electron scattering cross sections with cross sections calculated within the semi‐classical dielectric response model, which is implemented in the QUEELS‐ε(k,ω)‐REELS software (Quantitative analysis of Electron Energy Losses at Surfaces) [Surf. Interface Anal. 36 (2004) 824]. We also perform measurements and calculations for varying incident and exit angles of the electron, namely for angles to the surface normal between 15o and 75o, to check the validity of our results for all geometries. Our results show that the damping parameter of indium in the DL model for electron energy of 200 eV is three times larger than for energy of 2000 eV. Copyright © 2014 John Wiley & Sons, Ltd.

Over the last few decades, radiotherapy using high-energy proton beams over the range from 50 MeV to 250 MeV has been increasingly used and developed. Indeed, it offers the possibility to focus the dose in a very narrow area around the tumor cells. The tumor control is improved compared to radiotherapy using photon beams and the healthy cells around the tumor are not irradiated since the range of charged particles is limited. However, due to nuclear reactions of the incident charged particles in the tissue, secondary high-energy radiations, essentially photons and neutrons, are produced and irradiate the treatment room.As a consequence, thick concrete shielding walls are placed around the treatment room to ensure that other people and workers received a dose as small as possible. The dose measurement is performed with specific dosemeters such as the WENDI-II, which gives a conservative estimation of the ambient dose equivalent up to 5 GeV. The dose in working areas may also be estimated by means of numerical calculations by using simulation codes of particle transport such as the GEANT4, MCNPX, FLUKA and PHITS Monte Carlo codes.Secondary particle yields calculated with Monte Carlo codes show discrepancies when different physical models are used but are globally in good agreement with experimental data from the literature. Neutron and photon doses decrease exponentially through concrete shielding wall but the neutron dose is definitely the main component behind a wall with sufficient thickness. Shielding parameters, e.g. attenuation coefficients, vary as functions of emission angle (regarding the incident beam direction), incident proton energy, and target material and composition.The WENDI-II response functions computed by using different hadronic models show also some discrepancies. Thermal treatment of hydrogen in the polyethylene composing the detector is also of great importance to calculate the correct response function and the detector sensitivity.Secondary particle sources in a proton therapy facility are essentially due to losses in cyclotron and beam interactions inside the energy selection system, with the treatment nozzle components and the target - patient or phantom. Numerical and experimental results of the dose in mazes show a good agreement for the most of detection points while they show large discrepancies in control rooms. Indeed, statistical consistency is reached with difficulty for both experimental and calculated results in control rooms since concrete walls are very thick in this case./La radiotherapie utilisant des faisceaux de protons d’energie entre 50 MeV et 250 MeV s’est largement developpee ces dernieres annees. Elle a l’immense avantage de pouvoir concentrer la dose due au faisceau incident de maniere tres efficace et tres precise sur la tumeur, en epargnant les eventuels organes sains et sensibles aux radiations situes aux alentours. Cependant, des rayonnements « secondaires » tres energetiques sont crees par les reactions nucleaires subies par les protons lors de leur parcours dans les tissus, et peuvent sortir du patient. Des blindages entourant la salle de traitement et suffisamment epais doivent etre presents afin que la dose recue par les personnes se trouvant aux alentours soit la plus faible possible. La mesure de la dose se fait avec des dosimetres specifiques et sensibles aux rayonnements de haute energie, tels que le WENDI-II pour les neutrons. L’estimation de cette dose, et donc la modelisation des blindages, se fait egalement avec des codes de simulation numerique de transport de particules par les methodes de Monte Carlo, tels que GEANT4, MCNPX, FLUKA et PHITS.La production de rayonnements secondaires calculee a l’aide de codes Monte Carlo montre des ecarts significatifs lorsque differents modeles d’interactions physiques sont utilises, mais est en bon accord avec des donnees experimentales de reference. L’attenuation de la dose due aux neutrons et aux photons secondaires a travers un blindage compose de beton est exponentielle. De plus, la dose due aux neutrons est clairement la composante dominante au-dela d’une certaine epaisseur. Les parametres d’attenuation, comme par exemple le coefficient d’attenuation, dependent de l’angle d’emission (par rapport a la direction du faisceau incident), de l’energie des protons incidents et de la nature et la composition de la cible.La fonction de reponse du dosimetre WENDI-II montre egalement des variations lorsque differents modeles physiques sont consideres dans les codes Monte Carlo. La prise en compte d’effets fins comme les etats de vibration et de rotation des atomes d’hydrogene au sein du polyethylene composant le detecteur se revele essentielle afin de caracteriser correctement la reponse du detecteur ainsi que sa sensibilite.L’emission secondaire dans un centre de protontherapie est essentiellement due aux pertes dans le cyclotron et aux interactions du faisceau avec les systemes de selection de l’energie, les composants de la tete de tir et le patient (ou le fantome). L’evaluation numerique de la dose dans les labyrinthes des differentes salles du centre montre un bon accord avec les donnees experimentales. Tandis que pour les points de mesure dans leur salle de controle respective, de larges differences peuvent apparaitre. Ceci est en partie du a la difficulte d’obtenir des resultats statistiquement recevables du point de vue experimental, mais aussi numerique, au vu de l’epaisseur des blindages entourant les salles de controle.

Surface excitations significantly influence the measured peak intensities in elastic peak electron spectroscopy. They are characterised by the surface excitation parameter (SEP) defined as the change in excitation probability of an electron caused by the presence of the surface in comparison with an electron moving in an infinite medium. It is thus important to have a large database of SEP values or to have the possibility to determine it with a user‐friendly software. Recently, Novák developed the programme Software for Electron Solid Inelastic Interaction Parameter Calculations (SESINIPAC) within the model of Tung, Chen, Kwei and Chou, which allows to determine inelastic mean free path, differential inelastic mean free path, SEP and differential SEP for various energy loss function models and dispersion relations with as only input the energy loss function of the material. Using SESINIPAC, we calculate SEP for 27 different types of materials (metals, semiconductors and insulators) and for various angles and energies. We compare these results with those obtained previously with the software Quantitative Analysis of Electron Energy Losses at Surfaces (QUEELS), which uses the Yubero‐Tougaard model. We show that the dependence on angle of emission and energy is quite similar for the two models. However, the absolute values calculated with SESINIPAC are generally larger than those calculated with QUEELS, and the mean relative difference is 20% for metals and semiconductors but exceeds 50% for insulators. Copyright © 2012 John Wiley & Sons, Ltd.

The WENDI-II rem meter is one of the most popular neutron dosemeters used to assess a useful quantity of radiation protection, namely the ambient dose equivalent. This is due to its high sensitivity and its energy response that approximately follows the conversion function between neutron fluence and ambient dose equivalent in the range of thermal to 5 GeV. The simulation of the WENDI-II response function with the Geant4 toolkit is then perfectly suited to compare low- and high-energy hadronic models provided by this Monte Carlo code. The results showed that the thermal treatment of hydrogen in polyethylene for neutron 4 eV has a great influence over the whole detector range. Above 19 MeV, both Bertini Cascade and Binary Cascade models show a good correlation with the results found in the literature, while low-energy parameterised models are not suitable for this application.

Treatments delivered by proton therapy are affected by uncertainties on the range of the beam within the patient, requiring medical physicists to add safety margins on the penetration depth of the beam. To reduce these margins and deliver safer treatments, different projects are currently investigating real-time range control by imaging prompt gammas emitted along the proton tracks in the patient. This study reports on the feasibility, development and test of a new concept of prompt gamma camera using a slit collimator to obtain a one-dimensional projection of the beam path on a scintillation detector. This concept was optimized, using the Monte Carlo code MCNPX version 2.5.0, to select high energy photons correlated with the beam range and detect them with both high statistics and sufficient spatial resolution. To validate the Monte Carlo model, spectrometry measurements of secondary particles emitted by a PMMA target during proton irradiation at 160 MeV were realized. An excellent agreement with the simulations was observed when using subtraction methods to isolate the gammas in direct incidence. A first prototype slit camera using the HiCam gamma detector was consequently prepared and tested successfully at 100 and 160 MeV beam energies. Results confirmed the potential of this concept for real-time range monitoring with millimetre accuracy in pencil beam scanning mode for typical clinical conditions. If we neglect electronic dead times and rejection of detected events, the current solution with its collimator at 15 cm from the beam axis can achieve a 1-2 mm standard deviation on range estimation in a homogeneous PMMA target for numbers of protons that correspond to doses in water at the Bragg peak as low as 15 cGy at 100 MeV and 25 cGy at 160 MeV assuming pencil beams with a Gaussian profile of 5 mm sigma at target entrance.

Hard X-ray photoelectron spectroscopy (HXPS) using X-rays in the 1.5–15keV energy range generated by synchrotron sources becomes an increasingly important analysis technique due to its potential for bulk sensitive measurements. However, besides their high energy, another characteristic of photons generated by synchrotron sources is their linear polarization while X-rays from Al Kα or Mg Kα for instance are unpolarized. This difference implies a possible variation in total path travelled by the photoelectrons generated by the X-rays inside the medium and consequently a modification of the resulting spectrum shape. We show the influence of the polarization on the partial intensity distributions, namely the number of electrons escaping after n inelastic scattering events, for photoelectron with energies of 0.5, 1, 2, 3, 4 and 5keV and originating from Si 1s1/2, Cu 1s1/2, Cu 2p3/2, Au 4d3/2 and Au 4f7/2 subshells. Moreover, we point out the influence of the dipole approximation leading to an underestimation of the partial intensity distributions due to the neglect of the forward–backward asymmetry of the angular photoelectron distribution.