WILLIAM DE SOUZA SANTOS

WILLIAM DE SOUZA SANTOS

Página do item completo

Resultados de Busca

Agora exibindo 1 - 10 de 19

Monte Carlo approach for the determination of the angular dependence of an extrapolation chamber response
2019 - POLO, IVON O.; CALDAS, LINDA V.E.; SANTOS, WILLIAM S.
The angular dependence of an extrapolation chamber response is reported. The determination of the angular factors were carried out using the MCNP Monte Carlo Method. To determine the angular dependence, the PTW type 23392 extrapolation chamber of the Laboratory for Calibration of Instruments (LCI/IPEN) was simulated. The experiments were performed for the radiation fields of beta secondary standard BSS2 system sources. For the 90Sr/90Y source, the calibration distance of 11 cm without the beam flattening filter was used. For the 85Kr and 147Pm sources, the distances of 30 cm and 20 cm with the filter were used, respectively. The simulations were carried out by rotating the extrapolation chamber around the reference axis for angles between -90º and 90º, in steps of 5º. For the 90Sr/90Y source the angular dependence factor is greater than 1, predominating the dose build-up effect up to 60º and -60º, and the factor is less than 1 for the other angles, prevailing the absorption of beta particles. For the 85Kr and 147Pm sources, the angular dependence factor is less than 1 for all angles, predominating the absorption of beta particles too. The determined angular factors are in good agreement with the international report ISO 6980.
Uso de modelagem computacional para avaliação da exposição médica e ocupacional durante procedimento de cardiologia intervencionista
2020 - SANTOS, W.S.; NEVES, L.P.; PERINI, A.P.; CALDAS, L.V.E.
A cardiologia intervencionista (CI) é uma modalidade comum que utiliza imagens fluoroscópicas para o diagnóstico e a terapia de problemas cardiovasculares. Embora os equipamentos de fluoroscopia mais modernos empreguem sistema de redução de dose, além de feixes bem colimados, a radiação espalhada atinge órgãos circundantes do paciente que não estão localizados no feixe primário de radiação. A radiação espalhada pelo corpo do paciente acarreta a exposição ocupacional do médico intervencionista. A avaliação das exposições ocupacional e médica é importante para a determinação dos riscos e das consequências biológicas em diferentes órgãos e tecidos. Neste trabalho, a avalição foi feita por meio do conceito de coeficiente de conversão (CC). Para quantificar os valores de CC, foi utilizado o programa computacional MCNPX e o simulador antropomórfico masculino virtual adulto (MASH3), para representar o paciente e o médico. Os resultados comprovaram a eficiência da proteção dos equipamentos suspensos. Quando não utilizados, um aumento dos valores de CC de dose efetiva podem ser superiores a 1000%.
The use of personal protection equipment for the absorbed doses of eye lens and thyroid gland in CBCT exams using Monte Carlo
2020 - SOARES, MARIA R.; SANTOS, WILLIAM S.; NEVES, LUCIO P.; PERINI, ANA P.; BATISTA, WILSON O.G.; MAIA, ANA F.; BELINATO, WALMIR; CALDAS, LINDA V.E.
The purpose of this study was to evaluate the absorbed dose in the thyroid and eye lens when the patient uses individual protection. For this purpose, Monte Carlo (MC) simulation was employed using five different field of view (FOV) sizes, available in the i-Cat classic CBCT equipment. To represent the patient, a male virtual anthropomorphic phantom was used. Three different models of lead eyewear and thyroid shield were evaluated, as well as the dose difference with and without the personal protection equipment. The difference in the absorbed dose in relation to the use of the lead eyewear presented a reduction of 19% for the 8 cm×6 cm FOV (diameter×height), and 73% for the 14 cm×22 cm FOV. In relation to the thyroid, only the shield that involved the whole neck contributed to the reduction of the absorbed dose by up to 72% for a 14 cm×22 cm FOV. For the thyroid shields there was a maximum increase of 59% (14 cm×6 cm FOV), consequently, increasing the effective dose for the protocol. The results showed that the lead eyewear contributed to the protection of the eye lens, but the efficiency of the thyroid shield depends on several factors, as FOV and shield model.
Low cost electron irradiator using 90Sr+90Y sources
2020 - SILVA, ROGERIO M.V.; BELINATO, WALMIR; SANTOS, WILLIAM S.; SOUZA, LUIZA F.; PERINI, ANA P.; NEVES, LUCIO P.; SOUZA, DIVANIZIA N.
In beta therapy, β particles from 90Sr+90Y are used for the prevention and treatment of ophthalmological and dermatological diseases. For such purposes, the radiation dose is deposited by planar and concave applicators positioned on the region to be treated. Although this therapy is effective on the diseases, several complications have been reported, making these types of radioactive applicators obsolete in current clinical practice. This paper proposes a methodology to prepare and evaluate the safety of a research irradiator that re-purposes and adapts dermatologic and ophthalmic 90Sr+90Y applicators. The irradiator was constructed using low cost materials and three applicator sources. The sources are positioned at the center and the upper end of acrylic rectangular prisms. Radiochromic film was used to obtain the dose distribution on the sample holder surface. Pellets of aluminum oxide doped with carbon (Al2O3:C) were used to evaluate the reproducibility of the irradiator. The MCNPX Monte Carlo code was used for the evaluation of safety conditions. The irradiator exhibits good reproducibility of irradiation of dosimeters in pellet form and is safe to handle.
Evaluation of polymer gels using Monte Carlo simulations
2020 - SANTOS, CARLA J.; SANTOS, WILLIAM S.; PERINI, ANA P.; VALERIANO, CAIO C.S.; BELINATO, WALMIR; CALDAS, LINDA V.E.; NEVES, LUCIO P.
The use of Monte Carlo simulations in dosimetry is a well established area of research, and several correction factors, for ionization chambers, were evaluated with these simulations. Some simulated values were considered even more reliable than the experimental measurements. Besides these uses with ionization chambers, Monte Carlo simulations may also be employed in the development and characterization of new dosimetric materials, as polymer gels. They are largely employed in radiotherapy dosimetry to mimic human tissue. New polymer gels were studied in order to better represent different organs or tissues, to provide more reliable results, or even to use different measurement techniques. The objective of this study was to evaluate the dosimetric properties of polymer gels, in relation to its mass-energy absorption coefficients, energy response and tissue equivalence. For this purpose the MCNPX Monte Carlo code was utilized. Three different materials, employed in radiotherapy dosimetry were evaluated in this work: MAGAS, MAGAT and AMPS. For all simulations carried out, the values were within an acceptable uncertainty and in accordance to the expected results.
Computational dosimetry in a pediatric i-CAT procedure using virtual anthropomorphic phantoms
2020 - NEVES, LUCIO P.; FRANCO, ADRIANE B.; FRANÇA, MONIQUE; SOARES, MARIA R.; BELINATO, WALMIR; SANTOS, WILLIAM S.; CALDAS, LINDA V.E.; PERINI, ANA P.
The craniofacial structure is three-dimensional, and for a better visualization of these structures, Computed Tomography is often employed for diagnoses, even though being a high-cost procedure, leading to increased exposure to ionizing radiation. As a consequence, studies in dosimetry are necessary, since several radiosensitive structures are located in the head and neck, such as thyroid, crystalline and salivary glands. There is an overall consensus regarding the exposure of pediatric patients to ionizing radiation, with recommendations being that the procedures must occur with the shortest exposure time as possible, and it is only prescribed when they are effectively necessary. During the procedures, radiation effects are difficult to be measured. The use of either TL or OSL dosimeters can create artifacts within the images, and the positioning of a large number of dosimeters, necessary for the correct dose evaluation, is not feasible when it comes to a pediatric patient. Therefore pediatric virtual anthropomorphic phantoms and Monte Carlo simulations were used in this work. The absorbed and effective doses were determined during an i-CAT procedure, with 5 different fields of view, utilizing 5- and 10- year-old male virtual anthropomorphic phantoms. The results pointed out that the eye lens, salivary glands and thyroid received the highest doses. Besides, the effective dose values increase with the increasing of the FOV size, and the 5-year-old male virtual anthropomorphic phantom presented the highest effective dose values.
Characterization of an extrapolation chamber in beta radiation beams and Monte Carlo modelling
2020 - POLO, IVON O.; SANTOS, WILLIAM S.; CALDAS, LINDA V.E.
At the Calibration Laboratory (LCI) of the IPEN/CNEN, studies are in development on the establishment of a standard composed by the beta radiation sources for the dosimetry and calibration for personal monitoring in Brazil. For this purpose is used the Böhm extrapolation chamber (PTW model 23392). This chamber was already characterized at LCI in 90Sr/90Y beams using two different entrance windows: one of aluminized Mylar and another of PET (polyethylene terephthalate) known as Hostaphan. In this work, this extrapolation chamber was characterized in 85Kr and 147Pm beams. All tests were carried out with the reference 90Sr /90Y source, for comparison purposes. The Monte Carlo code MCNP5 code was used to obtain an extrapolation chamber and the BSS2 system sources computational model, based on the determination of the absorbed dose rate. Saturation curves, ion collection efficiency, ion recombination, polarity effect, stability of response, null depth, linearity of response, variation of response as a function of source-detector distance, extrapolation curves, correction factors and absorbed dose rates were obtained. The difference between the experimental absorbed dose rates and those obtained using the Monte Carlo model, compared to those from the calibration certificates, was less than 1.9% for the 108 histories for each BSS2 system source. All results of the performed tests are within the limits of the international recommendations. The results for the 90Sr/90Y source were in good agreement with previous works performed at LCI. These results are suitable for the establishment of a standard instrument for the dosimetry and calibration of beta radiation sources and detectors in the LCI/IPEN. This standard will allow the calibration of detectors in beta radiation beams in dosimetry services in Brazil.
An extrapolation chamber for the establishment of a primary radiation standard in 85Kr and 147Pm beta radiation beams
2019 - POLO, IVON O.; SANTOS, WILLIAM S.; CALDAS, LINDA V.E.
Introduction At the Calibration Laboratory (LCI) of the IPEN/CNEN, studies are in development on the establishment of the Böhm extrapolation chamber model 23392 as a primary standard system for the dosimetry and calibration of beta-radiation sources and detectors. This chamber was already characterized at the LCI in 90Sr/90Y beams using two different entrance windows: one of aluminized Mylar and another of Hostaphan. This extrapolation chamber was characterized in 85Kr and 147Pm beams. All tests were carried out with the reference 90Sr /90Y source, for comparative purposes. Methods A Keithley model 6517B electrometer was used for the measurements. The utilized radiation sources are part of the Beta Secondary Standard BSS2. Moreover, the Monte Carlo code MCNP5 was used to determine the absorbed dose rates and to compare them with the experimentally determined dose rates and with those from the PTB calibration certifi cate. Results Saturation curves, ion collection effi ciency, ion recombination, polarity effect, response stability, real null depth, linearity of response, variation of response as a function of sourcedetector distance, extrapolation curves, correction factors and absorbed dose rates were obtained. The ion collection effi ciency was greater than 99%; the ionic recombination was less than 1%, and the polarity effect was greater than 1%. The stability of the response was lower than 0.15% for the repeatability test, and it was less than 0.36% for the reproducibility test. The difference between the experimental absorbed dose rates and those from the Monte Carlo model, compared to those from the calibration certifi cate, was less than 1.9% for all sources. Conclusions All results of the performed tests are within the limits of the international recommendations. The results for the 90Sr/90Y source were in the good agreement with previous works performed at LCI. These results are suitable for the establishment of a primary standard for beta radiation.
Dose evaluation in breast brachytherapy using different 125I seeds
2019 - SANTOS, WILLIAM S.; SANTOS, CARLA J.; SILVA, ALINE F. da; SOUZA, SAMARA P.; NEVES, LUCIO P.; BELINATO, WALMIR; CALDAS, LINDA V.E.; PERINI, ANA P.
A very common type of cancer among women is the breast cancer. The treatment choice depends, among several factors, on the clinical stage of the disease and the age. One way to treat breast cancer is the permanent breast seed implant, with Iodine-125 (125I). Since they present some advantages: possibility to treat solid tumors, near the tumor site, induction of little trauma and strong lethality to cancer cells. In Brazil, a new 125I seed was developed at the Instituto de Pesquisas Energéticas e Nucleares to be applied in brachytherapy. Given the large number of women diagnosed with breast cancer, in this work, the dose determination in organs and tissues was undertaken, considering this new seed and a commercial, Amersham 6711-Oncoseed®, employing the Monte Carlo method. Moreover, for a better understanding of the radiation doses delivered to different patients, the breast volumes were modified. For this purpose, the MCNPX Monte Carlo code was utilized coupled with female virtual anthropomorphic phantoms. The results pointed out the highest dose values for the breast and skin. Furthermore, the dose results for both types of seeds were very similar.
Computational modelling of cervix uterus radiation procedure using a virtual anthropomorphic phantom and the MCNPX code
2019 - SANTOS, WILLIAM S.; NEVES, LUCIO P.; PERINI, ANA P.; SANTOS, CARLA J.; BELINATO, WALMIR; SILVA, ROGERIO M.V.; SOARES, MARIA R.; VALERIANO, CAIO C.; CALDAS, LINDA V.E.
There is a serious, and growing, concern about the increased risk of the emergence of a secondary cancer, radio-induced, associated with radiotherapy treatments. To assess the radiation doses to organs outside the target volume, in this work, several computational exposure scenarios were modelled, based on Monte Carlo simulation (MCNPX code). A Varian 2100c accelerator, and a female virtual anthropomorphic phantom were used, in a simulated treatment of cervical cancer. The determination of the dispersed dose would be important for assessing the risk in different organs or tissues. Four treatment fields were applied, varying the gantry angle. It was possible to observe that the conversion factors for equivalent dose were higher for the AP projection. For the RLAT and LLAT projections, the results were similar, fact that may be attributed to the symmetrical distributions of the organs in relation to the radiation source. The results presented in this work showed that the computational exposure scenario provides a versatile and accurate tool to estimate in a ready way the absorbed doses during a cervical treatment.