PAULA CRISTINA GUIMARÃES ANTUNES

PAULA CRISTINA GUIMARÃES ANTUNES

Página do item completo

Resultados de Busca

Agora exibindo 1 - 10 de 26

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.
Calculation of dose point kernel values for monoenergetic electrons and beta emitting radionuclides
2021 - MENDES, BRUNO M.; ANTUNES, PAULA C.G.; BRANCO, ISABELA S.L.; NASCIMENTO, EDUARDO do; SENIWAL, BALJEET; FONSECA, TELMA C.F.; YORIYAZ, HELIO
Targeted radionuclide therapy (TRT) and beta-emitting seeds brachytherapy (BSBT) exploit the characteristics of energy deposited by beta-emitting radionuclides. Monte Carlo (MC) modelling of electron transport is crucial for calculations of absorbed dose for TRT and BSBT. However, computer codes capable of providing consistent results are still limited. Since experimental validations show several difficulties, the estimation of electron dose point kernel (DPK) is often used to verify the accuracy of different MC codes. In this work, we compared DPK calculations for various point, isotropic and monoenergetic electron sources and several beta-emitting radioisotopes using the codes MCNP, EGSnrc, PENELOPE and TOPAS with different simulation options. The simulations were performed using latest versions of EGSnrc and Penelope, TOPAS version 3.3.1 and MCNP version 6.1 Monte Carlo codes. In our simulations, the geometrical model consists of a point electron source placed at the center of a water sphere emitting isotropically. The water sphere was divided into 28 shells and the energy deposition was scored within these shells. The radius of the outermost shell was 1.2R0, where R0 is the continuous slowing down approximation (CSDA) range. Five monoenergetic beta sources with energies of 0.05, 0.1, 0.5, 1 and 3 MeV were studied. Six beta-emitting radionuclides were also simulated: Lu-177, Sm-153, Ho-166, Sr-89, I-131 and Y-90. Monoenergetic electron simulations showed large deviations among the codes, larger than 13% depending on the electron energy and the distance from the source. In the cases where beta spectra of radionuclides were simulated, all MC codes showed differences from EGSnrc (used as reference value - RV) less than 3% within rE90 range (radius of the sphere in which 90% of the energy of the spectrum electrons would be deposited). TOPAS showed results comparable to EGSnrc and PENELOPE. DPK values for 0.1 MeV monoenergetic electrons, calculated using MCNP6, led to differences higher than ±5% from RV despite our attempts to tune electron transport algorithms and physics parameters.
MCMEG
2020 - FONSECA, T.C.F.; ANTUNES, P.C.G.; BELO, M.C.L.; BASTOS, F.; CAMPOS, T.P.; GERALDO, J.M.; MENDES, A.M.; MENDES, B.M.; PAIXÃO, L.; SANTANA, P.C.; SENIWAL, B.; SQUAIR, P.L.; YORIYAZ, H.
The improvement of the Monte Carlo (MC) community skills on computational simulations in Medical Physics is crucial to the field of radiotherapy as well as radiology. The Monte Carlo Modelling Expert Group (MCMEG) is an expert network specialized in MC radiation transport modelling and simulation applied to the radiation protection and dosimetry research fields. The MCMEG addressed a multigroup dosimetric intercomparison exercise for modelling and simulating a case of prostate radiation therapy (RT) protocol. This intercomparison was launched in order to obtain the dose distribution in the prostate target volume and in the neighboring organs. Dose assessments were achieved by using TLDs. A protocol using two pair of parallel-opposed fields were planned and performed with Alderson-Rando Pelvic Phantom. The assessed organs at risk were the urinary bladder, rectum and right and left femur heads. The RT simulations were performed using the MCNPx, MCNP6 and egs++ and BEAMnrc/DOSXYZnrc modules of EGSnrc Monte Carlo codes. The dose to the target volume, mean doses and standard deviation in the organs at risk, and dose volume data were computed. A comparison between the simulated results and the experimental values obtained from TLD measurements was made. In some cases the results obtained using MC simulations showed large deviations in comparison to the results obtained from the TLD measurements and these variations can be explained by the difficulties in the modelling of the geometry, selection of MC parameters required for the simulations and the statistical errors and inaccuracies in experimental measurements. Even though, the exercise has been a great opportunity for the MC groups to learn and share the main difficulties found during the modelling and the analysis of the results. Concerned to the obtained variations, the MCMEG team consider that this was expected for the level of complexity of the exercise and must be studied by the MC groups.
MCMEG
2018 - FONSECA, T.C.F.; SENIWAL, B.; MENDES, A.M.; BELO, M.C.L.; LACERDA, M.A.S.; MENDES, M.B.; PAIXÃO, R.L.; JOANA, G.S.; SANTANA, P.; MARQUES, J.; SQUAIR, L.P.; ANTUNES, P.; YORIYAZ, H.; BASTOS, F.
Photon energy-fluence correction factor in low energy brachytherapy
2017 - ANTUNES, PAULA C.G.; VIJANDE, JAVIER; GIMENEZ-ALVENTOSA, VICENT; YORIYAZ, HELIO; BALLESTER, FACUNDO
The AAPM TG-43 brachytherapy dosimetry formalism has become a standard for brachytherapy dosimetry worldwide; it implicitly assumes that charged-particle equilibrium (CPE) exists for the determination of absorbed dose to water at different locations. At the time of relating dose to tissue and dose to water, or vice versa, it is usually assumed that the photon fluence in water and in tissues are practically identical, so that the absorbed dose in the two media can be related by their ratio of mass energy-absorption coefficients. The purpose of this work is to study the influence of photon energy-fluence in different media and to evaluate a proposal for energy-fluence correction factors for the conversion between dose-to-tissue ( ) tis D and dose-to-water ( ) w D .State-of-the art Monte Carlo (MC) calculations are used to score photon fluence differential in energy in water and in various human tissues (muscle, adipose and bone) in two different codes, MCNP and PENELOPE, which in all cases include a realistic modeling of the 125I low-energy brachytherapy seed in order to benchmark the formalism proposed. A correction is introduced that is based on the ratio of the water-to-tissue photon energy-fluences using the large-cavity theory. In this work, an efficient way to correlate absorbed dose to water and absorbed dose to tissue in brachytherapy calculations at clinically relevant distances for low-energy photon emitting seed is proposed. The energy-fluence based corrections given in this work are able to correlate absorbed dose to tissue and absorbed dose to water with an accuracy better than 0.5% in the most critical cases.
Collision-kerma conversion between dose-to-tissue and dose-to-water by photon energy-fluence corrections in low-energy brachytherapy
2017 - GIMENEZ-ALVENTOSA, VINCENT; ANTUNES, PAULA C.G.; VIJANDE, JAVIER; BALLESTER, FACUNDO; PEREZ-CALATAYUD, JOSE; ANDREO, PEDRO
The AAPM TG-43 brachytherapy dosimetry formalism, introduced in 1995, has become a standard for brachytherapy dosimetry worldwide; it implicitly assumes that charged-particle equilibrium (CPE) exists for the determination of absorbed dose to water at different locations, except in the vicinity of the source capsule. Subsequent dosimetry developments, based on Monte Carlo calculations or analytical solutions of transport equations, do not rely on the CPE assumption and determine directly the dose to different tissues. At the time of relating dose to tissue and dose to water, or vice versa, it is usually assumed that the photon fluence in water and in tissues are practically identical, so that the absorbed dose in the two media can be related by their ratio of mass energy-absorption coefficients. In this work, an efficient way to correlate absorbed dose to water and absorbed dose to tissue in brachytherapy calculations at clinically relevant distances for low-energy photon emitting seeds is proposed. A correction is introduced that is based on the ratio of the water-to-tissue photon energy-fluences. State-of-the art Monte Carlo calculations are used to score photon fluence differential in energy in water and in various human tissues (muscle, adipose and bone), which in all cases include a realistic modelling of low-energy brachytherapy sources in order to benchmark the formalism proposed. The energy-fluence based corrections given in this work are able to correlate absorbed dose to tissue and absorbed dose to water with an accuracy better than 0.5% in the most critical cases (e.g. bone tissue).
Graphical interface for designing geometries and processing DICOM images for PENELOPE
2016 - GIMENEZ-ALVENTOSA, V.; ANTUNES, P.C.G.; BALLESTER, F.; VIJANDE, J.
One of he most dificult steps when preparing a Monte Carlo calculation is the design of their geometries. Such process is an error-prone, timeconsuming, and complex step for any simulation in the field of medical physics. The software VoxelMages has been developed to help the user in this complex task. It allows to design arbitrary geometries and to process DICOM image files for simulations with the general-purpose Monte Carlo code PENELOPE. Its main characteristics are described in the following.
Process map for FMEA risk analysis implementation by TG-100 of AAPM in Total Skin Electron Irradiation (TSEI) technique
2016 - IBANEZ-ROSELLO, B.; BAUTISTA-BALLESTEROS, J.A.; BONAQUE, J.; ANTUNES, P.C.G.; PEREZ-CALATAYUD, J.; GONZALEZ-SANCHIS, A.; LOPEZ-TORRECILLA, J.; BRUALLA-GONZALEZ, L.; GARCIA-HERNANDEZ, T.; VICEDO-GONZALEZ, A.; GRANERO, D.; SERRANO, A.; BORDERIA, B.; SOLERA, C.; ROSELLO, J.
Total Skin Electron Irradiation (TSEI) is a radiotherapy treatment which involves irradiating the entire body surface as homogeneously as possible. It is composed of an extensive multi-step technique in which quality management requires high consumption of resources. The TG-100 proposes a new perspective of quality management in radiotherapy, presenting a systematic method of risk analysis throughout the global flow of the stages through the patient. With the intention of applying this method, a multidisciplinary team of people was involved in the procedure that produced the process map (PM). This PM can be useful for those centers that intend to implement the TSEI technique. This is the first stage of a full risk analysis performed in a reference center in this treatment technique.
Study of CT/MRI mutual information based registration applied in brachytherapy
2016 - ANTUNES, P.C.G.; FONSECA, G.P.; VIJANDE, J.; BALLESTER, F.; GIMENEZ-ALVENTOSA, V.; YORIYAZ, H.
Brachytherapy (BT) is an advanced cancer treatment technique in which radioactive sources are placed in, or near, the tumor itself. This allows a high radiation dose in the tumor and reduces healthy tissues radiation exposure. The accuracy of the treatment plan depends on physical models and computer programs, which are directly related with the patient outcome. Recently, model-based dose calculations algorithms (MBDCAs) [1] have been made available. These are capable to handle tissue compositions/densities and other treatments complexities leading to more accurate dose distributions. Monte Carlo (MC) simulations have been proposed as an alternative to the implementation of MBCDAs due to their ability of achieve accurate radiation transport in realistic geometries. AMIGOBrachy is an MBDCA developed at Instituto de Pesquisas Energéticas Nucleares. It has been designed to create an user-friendly interface to integrate clinical treatment plans with MCNP6 [2]. This software provides the main resources required to process and edit images, import and edit treatment plans, set simulation parameters and analyze the results obtained. Currently, CT-based patient geometry allows the assignment of interaction cross sections to each voxel using density- Hounsfield units (HU) calibrations curves. However, due to the limited soft tissue contrast and image artefacts (high-density materials in a scanned object can lead to streaking artefacts) proper tissue segmentation may not be possible only through CT images [3]. MRI images introduce several additional imaging benefits, especially because of the superior soft-tissue contrast compared with CT. Many studies have investigated MRI and CT registration [4]. In this context, the purpose of this work is to study CT-MRI mutual information (MI) based registration [4,5] to improve future modelling in AMIGOBrachy using accurate anatomical representations (CT images) and excellent tissue contrast (MRI images). Image registration was performed using in-house algorithms developed using MATLAB software (Mathworks Inc., Natick, MA), version R2015. CT images were adopted as reference and MRI images as sensed [5]. The developed algorithm uses a two-step method. First, segmentation techniques are applied, such as: Thresholding, Growing Region and Resize. Then, transformation functions (rotation and translation) are used and a probabilistic approach based on voxel similarity (mutual entropy). Two images of the same patient were used in this study. The images were acquired in Instituto de Câncer do Estado de São Paulo (ICESP) for a gynaecologic treatment and were obtained immediately after inserting the applicator. The MI was determined for each translation and rotation in both x-axis and y-axis. The MI maximum value corresponds to the best fit between the images. The initial results allow a qualitative study of anatomical representation and improve target volume and structure delineation in AMIGOBrachy. The registration of the images shows geometric differences between CT and MRI due to geometrical deformation (inherent to the MRI images). The next step of this study is to obtain tissue composition and density from MRI images and implement an image module in AMIGOBrachy software. These improvements will significantly expand AMIGOBrachy software capabilities contributing to a more accurate treatment planning system.