PAULO DE TARSO DALLEDONE SIQUEIRA

PAULO DE TARSO DALLEDONE SIQUEIRA

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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.
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.
Levantamento da curva CT-to-ED para CBCT e seu uso na estimativa de dose em tratamento radioterápico de próstata
2020 - MELETTI, AMANDA F.; RIBEIRO, VICTOR A.B.; SIQUEIRA, PAULO T.D.; YORIYAZ, HELIO; SHORTO, JULIAN M.B.; NUNES, MAIRA G.; BARSANELLI, CRISTIANE
A fim de estimar a dose em pacientes em tratamento radioterápico de próstata, foi levantada a curva CT-to-ED para o sistema kv-CBCT XVI da Elekta e aplicado um método de sua correção para a região específica da pelve. O levantamento da curva foi feita por meio dos fantomas CatPhan® 503 e CIRS Pelvic e, para a sua correção, foram utilizadas as imagens de CBCT de 8 pacientes selecionados. A curva foi validada por meio de comparações entre a qualidade dos planejamentos calculados na Tomografia de Referência e na Tomografia de Feixe Cônico. Foram avaliados os histogramas de dose-volume (DVHs) e as distribuições de dose pelo critério gama – 3% e 3mm nos casos VMAT e 2% e 2mm nos 3D. Após a correção da curva, a diferença do cálculo da dose entre a CBCT e a CT de referência diminuiu, em média, de 4,7%±0,8% para 1,7%±1,1% nos planejamentos VMAT e de 3,2%±1,7% para 1,9%±1,6% nos planejamentos 3D. As aprovações nas análises gama subiram, em média, de 80,6%±3,5% para 99,1%±0,5% (VMAT) e de 84,3%±4,2% para 98,9%±1,0% (3D). Uma vez garantida a acurácia do cálculo na CBCT, a curva pode ser utilizada para verificar se a dose diariamente entregue ao paciente condiz com aquela que foi planejada e, caso contrário, ele pode ser beneficiado de replanejamento (e de compensação da dose) nas frações remanescentes de seu tratamento.
Estudo dos efeitos de composição e densidade de materiais tecido equivalentes na distribuição de dose longitudinal em protonterapia
2019 - BRANCO, ISABELA S.L.; ANTUNES, PAULA C.G.; SIQUEIRA, PAULO T.D.; SHORTO, JULIAN M.B.; YORIYAZ, HELIO
A eficiência de procedimentos radioterápicos depende do equilíbrio entre o fornecimento de altas doses conformadas ao volume tumoral e a restrição das doses recebidas pelos tecidos e órgãos saudáveis circundantes. Sendo uma modalidade de radioterapia, a protonterapia destaca-se neste cenário por possuir vantagens dosimétricas, que, quando combinadas com avanços tecnológicos, permitem que um grande potencial na conformidade da distribuição de dose. Este trabalho visa contribuir em um estudo dosimétrico, especificamente considerando os efeitos da heterogeneidade devido à presença de materiais tecido equivalentes com diferentes densidades e composições químicas, de modo a analisar qual destes parâmetros exerce maior influência na distribuição de dose longitudinal. A metodologia desenvolvida neste trabalho foi baseada em simulações de Monte Carlo com o código GEANT4 (através da interface TOPAS). Os objetos simuladores cilíndricos representados foram compostos inteiramente por diversos materiais tecido-equivalentes. Três grupos de estudo guiaram as simulações, o primeiro manteve a composição e densidade originais dos materiais, ao seguinte foi atribuída a todos os materiais heterogêneos a mesma densidade da água, mas mantiveram-se suas composições químicas originais; e por fim, foram realizadas simulações com as densidades originais dos materiais heterogêneos e composição química da água para todos os casos. Através da análise da distribuição de dose longitudinal variando com a profundidade, foi possível observar o comportamento da influência dos parâmetros de composição e densidade no alcance do feixe (d90) para os diferentes materiais e energias analisados. O estudo mostrou que, o efeito que a densidade dos materiais tecido equivalentes exerce sobre a deposição de dose é mais expressivo que o efeito de sua composição. A maior exatidão no range de tratamento permite evitar uma sub ou sobre dosagem da área irradiada. Esta é uma das diversas linhas de pesquisa que contribuem para a diminuição das incertezas em protonterapia.
Brachytherapyu dose measurements in heterogeneous tissues
2014 - FONSECA, GABRIEL P.; LUVIZOTTO, JESSICA; COELHO, TALITA S.; ANTUNES, PAULA C.G.; RUBO, RODRIGO; SIQUEIRA, PAULO de T.D.; YORIYAZ, HELIO
Spatial dose distribution determination in simple phantoms
2002 - YORIYAZ, H.; SIQUEIRA, P.T.D.; SANTOS, A.; GUIMARAES, M.I.C.C.; GARCEZ, A.T.
Studies on the radial dose distribution for clinical electron beams of 9 and 16 MEV using Monte Carlo simulation
2005 - YORIYAZ, H.; SIQUEIRA, P.T.D.; ZEVALLOS CHAVEZ, J.Y.; FURNARI, L.; POLI, M.E.R.
Construction tool and suitability of voxel phanton for skin dosimetry
2011 - ANTUNES, PAULA C.G.; SIQUEIRA, PAULO T.D.; FONSECA, GABRIEL P.; YORIYAZ, HELIO
Neutron flux and gama dose profile measurements and calculations along a phantom in the BNCT facility of IEA-R1 reactor
2010 - MUNIZ, R.O.R.; COELHO, P.R.P.; SILVA, G.S.A.; SIQUEIRA, P.T.D.; SOUSA, G.S.
A BNCT (Boron Neutron Capture Therapy) facility has been built at IEA-R1 reactor. The on going BNCT experiments demand the maximization of the thermal neutron component of the irradiation fi eld and the minimization of its epithermal and fast neutron components together with the reduction of the gamma contamination. This work was developed with the objective of evaluating whether the present radiation fi eld in the facility is suitable for carrying on BNCT studies and to establish a work methodology with phantoms in this facility. In order to achieve these objectives, thermal and epithermal neutron fl ux measurements, in the sample irradiation position were performed using hyper-pure Gold activation detectors and applying the Cadmium ratio. Absorbed dose due to gamma radiation was determined by TLD 400. A cylindrical phantom composed by acrylic discs was designed, built and tested in the facility. DOT 3.5 computational code was used to retrieve neutron fl uxes and the gamma dose estimates along the phantom. Although some improvements still need to be made in the methodology under implementation, computer simulations carried out with DOT code presented a good agreement with experimental data for most part of the evaluated profi le. In the position corresponding to about half the length of the phantom, the following experimental values were obtained: thermal neutron fl ux (2.52 ± 0.06)·108 n.cm-2.s-1, epithermal neutron fl ux (6.2 ± 0.3)·106 n.cm-2.s-1, absorbed dose due to thermal neutrons (4.2 ± 1.8) Gy and (10.1 ± 1.3) Gy due to gamma radiation. The obtained values show that the fl uxes of thermal and epithermal neutrons fl ux are appropriate for studies in BNCT, however, dose due to gamma radiation is high, indicating that the facility should be improved.