PAULO DE TARSO DALLEDONE SIQUEIRA
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Artigo IPEN-doc 30433 Efficient computational modeling of electronic stopping power of organic polymers for proton therapy optimization2024 - MATIAS, F.; SILVA, T.F.; KOVAL, N.E.; PEREIRA, J.J.N.; ANTUNES, P.C.G.; SIQUEIRA, P.T.D.; TABACNIKS, M.H.; YORIYAZ, H.; SHORTO, J.M.B.; GRANDE, P.L.This comprehensive study delves into the intricate interplay between protons and organic polymers, offering insights into proton therapy in cancer treatment. Focusing on the influence of the spatial electron density distribution on stopping power estimates, we employed real-time time-dependent density functional theory coupled with the Penn method. Surprisingly, the assumption of electron density homogeneity in polymers is fundamentally flawed, resulting in an overestimation of stopping power values at energies below 2 MeV. Moreover, the Bragg rule application in specific compounds exhibited significant deviations from experimental data around the stopping maximum, challenging established norms.Artigo IPEN-doc 30237 Comparison of methodologies for creating spread-out Bragg peaks in proton therapy using TOPAS and MCNP codes2023 - BRANCO, I.S.L.; BURIN, A.L.; PEREIRA, J.J.N.; SIQUEIRA, P.T.D.; SHORTO, J.M.B.; YORIYAZ, H.In proton beam treatments, the superposition of several weighted Bragg curves with different incident energies is required to homogeneously irradiate a large tumor volume, creating a spread-out Bragg peak (SOBP). This paper confirms on the suitability of two different methods to create SOBPs – Bortfeld/Jette’s and MCMC (Monte Carlo calculations and Matrix Computations), using Monte Carlo simulations performed with TOPAS and MCNP6.1. To generate the SOBPs, algorithms were developed for implementation of the two methods, which enabled to find the weights for thirty variations of SOBPs, categorized according to their width and maximum depths. The MCMC method used weight optimization in designing SOBPs to avoid negative values. In contrast, the Bortfeld/ Jette’s method yielded the SOBPs according to the variation of a power-law parameter (p) introduced by the range-energy relationship. Optimal values of p, from MCNP and TOPAS, were selected in order to retrieve SOBPs with the best smoothness and then related to those obtained from the literature. In comparing both methods and codes, dose homogeneity parameters (HOM) were used to examine the SOBP flatness and gamma analyses were employed to assess the dose deposition along its full extension. The results showed that the SOBPs designed using the MCMC method had better HOM values and computational performance for both codes when compared to the Bortfeld/Jette’s method. The gamma analyses highlighted significant differences between the entrance doses comparing the two different methods, for SOBPs with intermediate and high depths and small width. This evaluation was not possible with the HOM values alone, which stresses the relevance of a broad analysis to avoid unintended doses in healthy tissues.Artigo IPEN-doc 20609 Brachytherapyu dose measurements in heterogeneous tissues2014 - FONSECA, GABRIEL P.; LUVIZOTTO, JESSICA; COELHO, TALITA S.; ANTUNES, PAULA C.G.; RUBO, RODRIGO; SIQUEIRA, PAULO de T.D.; YORIYAZ, HELIOArtigo IPEN-doc 16945 Characterization of HDT Ir-192 source for 3D planning system2011 - FONSECA, GABRIEL P.; YORIYAZ, HELIO; ANTUNES, PAULA C.G.; SIQUEIRA, PAULO T.D.; RUBO, RODRIGO; MINAMISAWA, RENATO A.; FERREIRA, LOUISE A.Artigo IPEN-doc 16850 Study of discrete geometric representation in MCNP code2011 - ANTUNES, PAULA C.G.; SIQUEIRA, PAULO T.D.; FONSECA, GABRIEL P.; YORIYAZ, HELIO; CASTRO, VINICIUS A.Artigo IPEN-doc 17141 MCNP study the BFsub(3) detection efficiency2011 - CASTRO, VINICIUS A.; CAVALIERI, TASSIO A.; SIQUEIRA, PAULO T.D.; FEDORENKO, GIULIANA G.; COELHO, PAULO R.P.; MADI FILHO, TUFICResumo IPEN-doc 16478 Clinical electron beam chracteristics investigations using the Monte Carlo method for absorbed dose determination2007 - YORIYAZ, H.; SIQUEIRA, P.; POLI, M.; FURNARI, L.; RUBO, R.; RODRIGUES, L.; FONSECA, G.Artigo IPEN-doc 13680 Numerical analysis of an incremented statistical sampling procedure in MCNP2008 - SIQUEIRA, PAULO de T.D.; YORIYAZ, HELIO; SANTOS, ADIMIR dos; PASCHOLATI, PAULO R.MCNP has stood so far as one of the main Monte Carlo radiation transport codes. Its use, as any other Monte Carlo based code, has increased as computers perform calculations faster and become more affordable along time. However, the use of Monte Carlo method to tally events in volumes which represent a small fraction of the whole system may turn to be unfeasible, if a straight analogue transport procedure (no use of variance reduction techniques) is employed and precise results are demanded. Calculations of reaction rates in activation foils placed in critical systems turn to be one of the mentioned cases. The present work takes advantage of the fixed source representation from MCNP to perform the above mentioned task in a more effective sampling way (characterizing neutron population in the vicinity of the tallying region and using it in a geometric reduced coupled simulation). An extended analysis of source dependent parameters is studied in order to understand their influence on simulation performance and on validity of results. Although discrepant results have been observed for small enveloping regions, the procedure presents itself as very efficient, giving adequate and precise results in shorter times than the standard analogue procedure.Artigo IPEN-doc 14652 Physical models, cross sections, and numerical approximations used in MCNP and GEANT4 Monte Carlo codes for photon and electron absorbed fraction calculation2009 - YORIYAZ, HELIO; MORALLES, MAURICIO; SIQUEIRA, PAULO de T.D.; GUIMARAES, CARLA da C.; CINTRA, FELIPE B.; SANTOS, ADIMIR dosPurpose: Radiopharmaceutical applications in nuclear medicine require a detailed dosimetry estimate of the radiation energy delivered to the human tissues. Over the past years, several publications addressed the problem of internal dose estimate in volumes of several sizes considering photon and electron sources. Most of them used Monte Carlo radiation transport codes. Despite the widespread use of these codes due to the variety of resources and potentials they offered to carry out dose calculations, several aspects like physical models, cross sections, and numerical approximations used in the simulations still remain an object of study. Accurate dose estimate depends on the correct selection of a set of simulation options that should be carefully chosen. This article presents an analysis of several simulation options provided by two of the most used codes worldwide:MCNP and GEANT4. Methods: For this purpose, comparisons of absorbed fraction estimates obtained with different physical models, cross sections, and numerical approximations are presented for spheres of several sizes and composed as five different biological tissues. Results: Considerable discrepancies have been found in some cases not only between the different codes but also between different cross sections and algorithms in the same code. Maximum differences found between the two codes are 5.0% and 10%, respectively, for photons and electrons. Conclusion: Even for simple problems as spheres and uniform radiation sources, the set of parameters chosen by any Monte Carlo code significantly affects the final results of a simulation, demonstrating the importance of the correct choice of parameters in the simulation.