Displacements approach with external variables only for multi-domain analysis via symmetric BEM

In the present paper a new displacement method, defined as external variables one, is proposed inside the multidomain symmetric Boundary Element formulation. This method is a natural evolution of the displacement approach with interface variables in the multidomain symmetric BEM analysis. Indeed, the strategy employed has the advantage of considering only the kinematical quantities of the free boundary nodes and the algebraic operators involved show symmetry and very small dimensions. The proposed approach is characterized by strong condensation of the mechanical and kinematical boundary nodes variables of the macro-elements. All the domain quantities, such as tractions and stresses, displacements and strains, are computed through the Somigliana Identities in a subsequent phase. Some examples are shown using the calculus code Karnak.sGbem, by which it was possible to make some comparisons with analytical solutions andothe rapproaches to show the effectiveness of the method propose

Phenol compounds for Electron Spin Resonance dosimetry in gamma and neutron field

The use of neutrons for cancer treatments has stimulated the research for beam characterization in order to optimize the therapy procedures in Neutron Capture Therapy (Altieri, 2008). Several research laboratories have shown an increasing interest aimed at extending the applicability of Electron Spin Resonance (ESR) dosimetry to radiotherapy with different types of radiation beams. In particular, ESR spectrometry provides absorbed dose measurements through the detection of the stable free radicals produced by ionizing radiations. The ESR dosimetric method has many advantages such as simple and rapid dose evaluation, the readout procedure is non-destructive, linear response of many organic and inorganic compounds (Baffa 2014). In this work we study the response of phenolic compounds with and without gadolinium addition for electron spin resonance (ESR) dosimetry exposed to a gamma and mixed (n, gamma) field mainly composed of thermal neutrons. The compound IRGANOX 1076 phenol gives a phenoxy radical stabilized by the presence of two bulky groups [3]. Moreover, its high molecular weight, the low volatility and the compatibility with the dosimeter binding material (paraffin) are advantages with respect to lower molecular weight phenols. In this work we report the ESR investigation of phenols pellets and thin films with and without Gd2O3 (5% by weight) exposed in the thermal column of the Triga Mark II reactor of LENA of Pavia. Thanks to their size, the phenolic films here presented are good devices for the dosimetry of beams with high dose gradient and which require accurate knowledge of the precise dose delivered. The choice of Gd as the additive nucleus has been made because we are interested in applications for mixed field (neutrons/photons) Gd-ESR dosimetry has an high neutron capture cross section and, furthermore, the high LET secondary particles release their energy entirely in the dosimeter. The low content of gadolinium guarantees a good tradeoff between the sensitivity to thermal neutrons. However, the use of gadolinium reduces or abolishes tissue equivalence because of its high atomic number (Marrale, 2015). The dosimetric features of these ESR dosimeters have been investigated. In particular, we analyzed the ESR spectra of these compounds and their dependence on microwave power and modulation amplitude, their response after gamma and neutron irradiations, the detection limits for both beam typologies, signal stability after irradiation. The results of ESR experiments are compared with Monte Carlo simulations aimed at obtaining information about the total dose measured by means of ESR dosimeters

Multidomain SBEM analysis for two dimensionalelastoplastic-contact problems

The Symmetric Boundary Element Method based on the Galerkin hypotheses has found application in the nonlinear analysis of plasticity and contact-detachment problems, but dealt with separately. In this paper we wants to treat these complex phenomena together. This method works in structures by introducing a subdivision into sub-structures, distinguished into macroelements, where elastic behaviour is assumed, and bem-elements, where it is possible for plastic strains to occur. In all the sub-structures, elasticity equations are written and regularity conditions in weighted (weak) form and/or in nodal (strong) form between boundaries have to be introduced, to attain the solving equation system

Phenol compounds as new materials for Electron Paramagnetic Resonance dosimetry in clinical photon and electron beams,

In the last decades several research laboratories have shown an increasing interest aimed at extending the applicability of Electron Paramagnetic Resonance (EPR) dosimetry to radiotherapy with different types of radiation beams. EPR is a spectroscopic method for investigating the structure and dynamics of such paramagnetic species. Free radicals are known to be produced when a compound is irradiated with ionizing radiations. The concentration of radiation-induced free radicals is proportional to the energy released inside in the medium and this allows for dosimetric measurements through EPR technique. The use of alanine as a dosimetric material gave the possibility to apply EPR spectroscopy for high-dose standardization and dose control in radiation processing (Marrale 2016). The EPR dosimetric method has many advantages such as simple and rapid dose evaluation, the readout procedure is non-destructive, linear response of many organic and inorganic compounds. EPR detectors show a behavior that suggest possible applications for various kinds of beams used for radiation therapy. Nowadays, the most widely used organic compound as a dosimeter is the alanine. However, many researches are in progress with the aim at improving sensitivity of EPR dosimetry for doses much smaller than 1 Gy. More sensitive materials than alanine are needed to make the EPR dosimeter competitive with other dosimetry systems. Our research group has started an investigation of the EPR response of some phenols compounds for possible EPR dosimetric applications suitable features, such as high efficiency of radiation-matter energy transfer and radical stability at room temperature. Phenols are compounds possessing a benzene ring attached to a OH group. After irradiation the final product is a stable phenoxy radical. The stability of such radical can be improved by adding other alkyl chains which can be attached to the benzene ring. The phenol octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate gave interesting results. Moreover, its high molecular weight, the low volatility and the compatibility with the dosimeter binding material (wax) are advantages with respect to lower molecular weight phenols. In this work we report the EPR investigation of phenols exposed to clinical photon and electron beams (Gallo, 2016). The dosimetric features of these EPR dosimeters (dependence on microwave power and modulation amplitude, their response after gamma and electron irradiations, dependence on beam type and energy, the detection limits for both beam typologies, signal stability after irradiation) were investigated and the results are reported

Electron Spin Resonance dosimetry using organic compounds (alanine and ammonium tartrate) for mixed neutron-gamma fields

Alongside with the development of Neutron Capture Therapy (NCT) and the use of thermal neutrons for radiotherapeutic purposes, many efforts have been devoted to the characterization of the beam in order to optimize therapy procedures. Reliable dose measurements should be able to determine the various (neutrons and photonic) components of the mixed beam usually employed for therapy. This paper studies the effect of additives such as boric and gadolinium nuclei on the sensitivity of neutron organic (alanine and ammonium tartrate) dosimeters analyzed through Electron Spin Resonance (ESR) technique (Marrale, 2014). These dosimeters were exposed to a mixed (neutron-gamma) field mainly composed of thermal neutrons. The choice of 10B and 64Gd as nuclei additives is due to their very high capture cross section for thermal neutrons. Also, after the nuclear reaction with thermal neutrons are emitted particles, which in turn release their energy in the vicinity of the reaction site (Marrale, 2008). The irradiation with mixed field (neutron-gamma) were performed within the thermal column of the TRIGA reactor, University of Pavia. Dosimeters readout was performed through the Electron Spin Resonance spectrometer Bruker ECS106 located at the Laboratory of Dosimetry ESR / TL of the Department of Physics and Chemistry - University of Palermo. We found that the addition of Gadolinium allows to largely increase the sensitivity of the dosimeters for thermal neutrons. In particular, a low concentration (5% by weight) of gadolinium oxide leads to an improvement of the sensitivity of neutrons more than 10 times. In addition, for this low content of gadolinium the photon tissue equivalence is not heavily reduced. This experimental analyses are compared with computational analyses carried out by means of Monte Carlo simulations performed with the MCNP (Monte Carlo N-Particle) transport code. A good agreement was observed for alanine dosimeters

Comparison of EPR response of pure alanine and alanine with gadolinium dosimeters exposed to TRIGA Mainz reactor

The development of Neutron Capture Therapy (NCT) for cancer treatments has stimulated the research for beam characterization in order to optimize the therapy procedures. The NCT has found to be promising for treatments of tumours which hardly can be treated with other techniques, such as gliomas. Alongside with the improvements of this technique, the development of procedures for the beam characterization arouses great interest in order to optimize the therapy protocol by reliably determining the various (neutronic and photonic) components of the mixed beam usually employed for therapy. Electron Paramagnetic Resonance (EPR) dosimetry for electron and photon beams with alanine has attracted the attention of many research groups for dosimetric purposes. Furthermore, the applications of EPR dosimetry for high LET radiation beams, such as carbon ions and neutrons, are continuously increasing. This is because of the very good dosimetric features of alanine EPR detectors such as: tissue equivalence for photon beams, linearity of its dose-response over a wide range, high stability of radiation induced free radicals, no destructive read-out procedure, no need of sample treatment before EPR signal measurement and low cost of the dosimeters. Moreover, in order to improve the sensitivity to thermal neutrons of alanine dosimeters the addition of nuclei such as gadolinium oxidewas previously studied. The choice of Gd as additive nucleus is due to its very high capture cross section to thermal neutrons and to the possibility for secondary particles produced after interaction with thermal neutrons of releasing their energy in the neighbourhood of the reaction site. In particular, it was found that low concentration (i.e. 5% by weight) of gadolinium oxide brings about an neutron sensitivity enhancement of more than 10 times without heavily reducing tissue equivalence. We have studied the response of alanine pellets with and without gadolinium exposed to the thermal column of the TRIGA Mark II research reactor at the University of Mainz. Pure alanine dosimeters used were produced by Synergy Health (Germany) whereas the Gd-added dosimeters were produced at the University of Palermo. The irradiations were performed inside polyethylene holders to guarantee charged particles equilibrium conditions. The results of EPR experiments are compared to Monte Carlo (MC) simulations aimed at obtaining information about the contribution of the various components to the total dose measured by means of EPR dosimeters. For alanine dosimeters a good agreement between experimental data and MC simulation have been achieved

EPR/alanine dosimetry for verification in Helical Tomotherapy Stereotactic Radiosurgery (HTSRS) treatments

Introduction Intracranial stereotactic radiosurgery (SRS) is a technique to deliver an ablative radiation dose with an extremely sharp dose gradient to small brain tumors. In this study the accuracy of the dose delivered in SRS by a non conventional radiotherapy machine, the TomoTherapy Hi-Art System, was investigated using an "end-to-end" test using alanine pellets and gafchromic films. Methods Dose verifications were made using alanine dosimeters placed in an antropomorphic head phantom (Alderson Rando Phantom) under different treatment conditions in case of both single and multiple brain tumors. 1.25mm slice kVCT scan of the phantom was used to generate SRS plans on the TomoTherapy Planning Station platform. Commercial alanine dosimeters (Synergy Health, Germany) were irradiated in various positions of the phantom. EPR measurements were carried out through Bruker spectrometer at room temperature. Results The dose values for 6 different possible clinical scenarios characterized by the presence of one, two or three tumor lesions were reconstructed by means of alanine dosimeters and gafchromic films. The dose values measured through both experimental techniques show a good agreement with the dose values calculated by the TomoTherapy Treatment Planning System, for both tumors and organs at risk (such as optical chiasma and brain stem). Conclusion Alanine absolute dose measurements showed to be useful for the dosimetric validation of HT SRS treatments

Characterization of phenolic solid state pellets for ESR dosimetry with radio-therapeutic photon and electron beams

IIntroduction Among the various dosimetric techniques used for characterizing the radiation beams used in radiation therapy, the electron spin resonance (ESR) arouses increasing interest for applications in various therapy procedures. In this work we report the ESR investigation of particular phenol compound (IRGANOX 1076) exposed to clinical photon and electron beams (Gallo et al., 2017). Methods Phenol (IRGANOX 1076 - Sigma Aldrich) pellets were produced also with paraffin (10% by weight). Phenol pellets were exposed to clinical photon and electron beams at various energies produced by a linear accelerator (LINAC) Siemens Primus (Siemens Medical Systems, CA, USA) installed at the Radiotherapy Department of A.R.N.A.S. \u2013 Hospital Civico-Di Cristina-Benfratelli (Palermo) with absorbed doses ranging between 0 and 13 Gy. ESR measurements were performed through a X band Spectrometer. Readout parameters were optimized to maximise the signal without excessive spectrum distortions. Results Basic dosimetric properties of phenolic dosimeters, such as reproducibility, dose-response, sensitivity,linearity and dose rate dependence were investigated. A satisfactory intra-batch reproducibility of the ESR signal of the manufactured dosimeters was obtained. The analysis of the ESR signal as function of absorbed dose highlights that the response of this material is linear in the dose range investigated (1-13 Gy) and is independent of the beam energy. The presence of an intrinsic background signal limits the minimum detectable dose to a value of approximately 0.6 Gy. Reliable and accurate assessment of the dose was achieved, independently of the dose rate. The dosimeters were tested by measuring the depth dose profile of a 6 MV photon beam. Conclusion Such characteristics, together with the fact that IRGANOX 1076\uae is almost tissue-equivalent, and the stability of the ESR signal, make these dosimeters promising materials for ESR dosimetric applications in radiotherapy

Energetic criterion of the error evaluation in the analysis via SGBEM

The Symmetric Galerkin Boundary Element Method (sGbem) is assuming more and more an effective role in the solving problems of mechanics in different fields of engineering [1]. The presence of symmetric and defined in sign algebraic operators make such Method more competitive in comparison to the formulation for collocation. The present work has as objective the improvement of the response in the process of analysis of the system where a first discretizazion has been operated, by using a strategy that allows to operate a estimate of the error. On the base of such estimate it is possible to operate a new discretizazion of the boundary through adaptive procedures