PAULO DE TARSO DALLEDONE SIQUEIRA

PAULO DE TARSO DALLEDONE SIQUEIRA

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Development of a sample exchange system for irradiations in the BH-3 channel of the IEA-R1 reactor at IPEN
2024 - PAULA, M.L. de; MORALLES, M.; GENEZINI, F.A.; SIQUEIRA, P.T.D.; RIBEIRO JUNIOR, I.S.; SILVA JUNIOR, I.A. da
This work was developed with the aim of improving the current sample exchange system of the BH-3 irradiation channel of the IEA-R1 reactor at IPEN. The instrument's operating concept will provide a better use of the irradiation space as well as greater safety and confidence to the operator. The development of the system involved 3D modeling, sizing, construction and non-destructive testing of the various parts, and analysis of neutron-induced activation of the materials most exposed to the beam. A programmable logic controller (PLC) was implemented for the system’s control inside a dedicated electrical panel that was built with materials compatible with the location. The system was designed to support samples weighing up to 15 kg. Bench tests were carried out and showed that the system performs the necessary functions to accurately position samples in three locations: outside the biological shield, at the irradiation channel and at the decay waiting station. The implementation of this instrument will contribute to the application of the ALARA principle in the operator activities at the BH-3 irradiation channel.
Study of the behavior of 3 MeV proton beams on PMMA
2024 - PEREIRA, J.; MATIAS, F.; ANTUNES, P.; SHORTO, J.; SIQUEIRA, P.; SILVA, T.; RODRIGUES, C.; OTUBO, L.; FERREIRA, G.; YORIYAZ, H.
Efficient computational modeling of electronic stopping power of organic polymers for proton therapy optimization
2024 - 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.
Thermal neutron dose measurements using TLD-100 detectors in the IPEN/MB-01 reactor core
2024 - CAVALIERI, TASSIO A.; SIQUEIRA, PAULO de T.D.; SHORTO, JULIAN M.B.; YORIYAZ, HELIO
Considerable experimental effort has been aimed at uncovering a reliable way to perform a dosimetric assessment in mixed radiation fields. In fields composed by gammas and neutrons, TLD dosimeters are usually applied to execute such measurements, although there is no consensus on the most favorable strategy to employ them. In this context, TLD-100 measurements within two different core configurations of the IPEN/MB-01 research reactor and Monte Carlo simulations have been used to investigate the behavior of those detectors in multiple mixed radiation fields, deriving a methodology to evaluate the dose deposition in the dosimeter by different gamma and neutron energy spectra and intensities. A surprising outcome is the linear neutron dose response shown by TLD-100 even irradiated by so distinct irradiation fields.
Heterogeneous physical phantom for I-125 dose measurements and dose-to-medium determination
2024 - ANTUNES, PAULA C.G.; SIQUEIRA, PAULO de T.D.; SHORTO, JULIAN M.B.; YORIYAZ, HELIO
PURPOSE: In this paper we present a further step in the implementation of a physical phantom designed to generate sets of “true”independent reference data as requested by TG-186, intending to address and mitigate the scarcity of experimental studies on brachytherapy (BT) validation in heterogeneous media. To achieve this, we incorporated well-known heterogeneous materials into the phantom in order to perform measurements of 125I dose distribution. The work aims to experimentally validate Monte Carlo (MC) calculations based on MBDCA and determine the conversion factors from LiF response to absorbed dose in different media, using cavity theory. METHODS AND MATERIALS: The physical phantom was adjusted to incorporate tissue equivalent materials, such as: adipose tissue, bone, breast and lung with varying thickness. MC calculations were performed using MCNP6.2 code to calculate the absorbed dose in the LiF and the dose conversion factors (DCF). RESULTS: The proposed heterogeneous phantom associated with the experimental procedure carried out in this work yielded accurate dose data that enabled the conversion of the LiF responses into absorbed dose to medium. The results showed a maximum uncertainty of 6.92 % ( k = 1), which may be considered excellent for dosimetry with low-energy BT sources. CONCLUSIONS: The presented heterogeneous phantom achieves the required precision in dose evaluations due to its easy reproducibility in the experimental setup. The obtained results support the dose conversion methodology for all evaluated media. The experimental validation of the DCF in different media holds great significance for clinical procedures, as it can be applied to other tissues, including water, which remains a widely utilized reference medium in clinical practice.
Comparison of methodologies for creating spread-out Bragg peaks in proton therapy using TOPAS and MCNP codes
2023 - 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.
Avaliação da sensibilidade do ArcCHECK na detecção de erros de posicionamento do MLC
2023 - BIAGIONI, FERNANDA G.; CAMPANELLI, HENRIQUE B.; RIBEIRO, VICTOR A.B.; SIQUEIRA, PAULO T.D.; SHORTO, JULIAN M.B.; SERANTE, ALEXANDRE R.
Técnicas modernas de tratamento como a técnica de Arcoterapia Volumétrica Modulada (VMAT, do inglês Volumetric Modulated Arc Therapy) têm sido amplamente utilizadas na prática clínica para diversas regiões de tratamento e a avaliação do efeito dosimétrico devido a erros de posicionamento do multileaf (MLC) tem sido estudada por alguns autores. O objetivo desse trabalho foi avaliar a sensibilidade do ArcCHECK em detectar erros de posicionamento do MLC em campos estáticos, em arcos estáticos e para planejamentos do AAPM TG-119 usando análise gamma com os critérios de 3%/3 mm, 3%/2 mm e 2%/2 mm. Os resultados encontrados sugerem que o ArcCHECK é sensível para detectar erros sistemáticos e randômicos maiores do que 2 mm, nos casos do AAPM TG-119 utilizando os critérios gamma de 3%/3 mm, 3%/2 mm 2%/2 mm. Porém usar apenas análise gamma possibilita que alguns erros não sejam detectados na prática clínica, se a porcentagem de pontos aprovados com índice gamma é maior que o índice de confiança da instituição.
Análise comparativa de modelos matemáticos no desenvolvimento de um Algoritmo Pencil Beam para protonterapia
2023 - BRANCO, I.S.L.; SIQUEIRA, P.T.D.; SHORTO, J.M.B.; YORIYAZ, H.
Introdução: Em protonterapia, a distribuição de dose é calculada por meio de algoritmos analíticos, como o Algoritmo Pencil Beam (PBA), que requer a estimativa de parâmetros para a fluência no ar e dose na água. Este estudo utilizou o código TOPAS para modelar o feixe e analisou a influência dos modelos matemáticos no cálculo de dose com o PBA. Materiais e Métodos: Simulações com o TOPAS calcularam a fluência no ar, dose elementar na água e dose de referência para prótons de 187 MeV. Três distintos modelos matemáticos parametrizaram a distribuição de fluência no ar e cinco a dose elementar na água, resultando em 15 convoluções que foram comparadas com a dose de referência. A Figura 1 apresenta as diferenças relativas de dois dos resultados obtidos. Resultados e Discussões: Entre as convoluções realizadas, destaca-se a que utilizou a fluência ajustada com a Gaussiana Dupla e a dose elementar com a Gaussiana Dupla e Cauchy. Essa convolução apresentou pequenas diferenças relativas nas doses laterais de entrada do feixe e menores diferenças quando comparadas aos outros modelos. Conclusões: A precisão dos cálculos de dose no PBA é grandemente influenciada pela escolha dos modelos matemáticos para parametrizar a fluência e dose elementar, especialmente para baixas doses (distantes do eixo central).
A versatile physical phantom design and construction for I-125 dose measurements and dose-to-medium determination
2023 - ANTUNES, PAULA C.G.; SIQUEIRA, PAULO de T.D.; SHORTO, JULIAN M.B.; YORIYAZ, HELIO
PURPOSE: In this paper we present a phantom designed to provide conditions to generate set of “true” independent reference data as requested by TG-186, and mitigating the scarcity of experimental studies on brachytherapy validation. It was used to perform accurate experimental measurements of dose of 125I brachytherapy seeds using LiF dosimeters, with the objective of experimentally validating Monte Carlo (MC) calculations with model-based dose calculation algorithm (MBDCA). In addition, this work intends to evaluate a methodology to convert the experimental values from LiF into dose in the medium. METHODS AND MATERIALS: The proposed PMMA physical phantom features cavities to insert a LiF dosimeter and a 125I seed, adjusted in different configurations with variable thickness. Monte Carlo calculations performed with MCNP6.2 code were used to score the absorbed dose in the LiF and the dose conversion parameters. A sensitivity analysis was done to verify the source of possible uncertainties and quantify their impact on the results. RESULTS: The proposed phantom and experimental procedure developed in this work provided precise dose data within 5.68% uncertainty (k = 1). The achieved precision made it possible to convert the LiF responses into absorbed dose to medium and to validate the dose conversion factor methodology. CONCLUSIONS: The proposed phantom is simple both in design and as in its composition, thus achieving the demanded precision in dose evaluations due to its easy reproducibility of experimental setup. The results derived from the phantom measurements support the dose conversion methodology. The phantom and the experimental procedure developed here can be applied for other materials and radiation sources.
Influence dosimetric study of different couches in radiotherapy treatments
2022 - DEL NERO, R.A.; EMILIOZZI, C.Z.S.; SIQUEIRA, P.T.D.; ANTUNES, P.C.G.; SERANTE, A.R.
Radiotherapy is a recommended procedure for 52% of cancer cases, in average, as one of the treatment forms, therefore, it is important for the clinical practice to investigate the affecting factors in dose distribution received by the patients, such as immobilization devices and treatment couch. With the introduction of treatments with modulated intensity techniques like IMRT and VMAT, the number of incidence fields used for patient treatment increased, making couch’s dosimetric effect more significant in these modalities. The attenuation data acquisition referring to the treatment couches, as well as the TPS data evaluation, show important parameters for the clinical practice because they influence what happens with the dose delivery during the treatment, ensuring a better quality and safety to the treatments. This research presents experimental results evaluating the couch’s impact in the treatments by a study of perturbation in the distribution of surface dose, and dose attenuation according to the gantry’s angle for the couches BrainLABTM, ExactTM and iBEAMTM. Then we propose better density values for the couches BrainLABTM and ExactTM for their inclusion in EclipseTM TPS. Lastly, we compare the dose difference considering the presence or not of couch in the planning. In conclusion, the beam’s attenuation increase by the couches and the doses alterations on the skin must be taken in consideration in the treatment planning process. It is of great relevance that each treatment center perform internal tests to determinate the best density values for available TPS.