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.
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.
Reconstruction of segmented human voxel phantoms for skin dosimetry
2009 - ANTUNES, PAULA C.G.; SIQUEIRA, PAULO de T.D.; YORIYAZ, HELIO; FONSECA, GABRIEL P.; REIS, GABRIELA; FURNARI, LAURA
High-resolution medical images along with methods that simulate the interaction of radiation with matter, as the Monte Carlo radiation transport codes, have been widely used in medical physics procedures. These images provide the construction of realistic anatomical models, which after being coupled to these codes, may drive to better assessments of dose distributions on the patient. These anatomical models constructed from medical images are known as voxel phantoms (voxel - volume element of an image). Present day regular images are unsuitable to correctly perform skin dose distribution evaluations. This inability is due to improper skin discrimination in most of the current medical images, once its thickness stands below the resolution of the pixels that form the image. This paper proposes the voxel phantom reconstruction by subdividing and segmentating the elements that form the phantom. It is done in order to better discriminate the skin by assigning it more adequate thickness and actual location, allowing a better dosimetric evaluation of the skin. This task is an important issue in many radiotherapy procedures. Particular interest lays in Total Skin Irradiation (TSI) with electron beams, where skin dose evaluation stands as the treatment key point of the whole body irradiation. This radiotherapy procedure is under implementation at the Hospital das Clínicas da Universidade de São Paulo (HC-USP).
Clinical electron beam chracteristics investigations using the Monte Carlo method for absorbed dose determination
2007 - YORIYAZ, H.; SIQUEIRA, P.; POLI, M.; FURNARI, L.; RUBO, R.; RODRIGUES, L.; FONSECA, G.
Monte Carlo simulation as an auxiliary tool for electron beam quality specification for intra-operative radiotherapy
2005 - CASTRO NETO, ALUISIO J. de; HADDAD, CECILIA M.K.; PELOSI, EDILSON L.; ZEVALLOS CHAVEZ, JUAN Y.; YORIYAZ, HELIO; SIQUEIRA, PAULO de T.D.
Intra-operative radiotherapy (IORT) using electron beams has demonstrated to be a good alternative as part of the breast-conserving surgery. Besides, as the computer processing capacity has been increasing along the years, it has become a potential auxiliary tool in radiotherapy treatment planning. In this work these streams are merged together: simulations were performed by different Monte Carlo radiation transport codes (EGS4 and MCNP in its releases 4C and 5) in an attempt to not only examine the efficacy of Al and Pb discs used in IORT procedures to protect critical regions but also to compare the performance of the forementioned codes.