WILLIAM DE SOUZA SANTOS
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Artigo IPEN-doc 27216 The use of personal protection equipment for the absorbed doses of eye lens and thyroid gland in CBCT exams using Monte Carlo2020 - 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.Artigo IPEN-doc 27202 Computational dosimetry in a pediatric i-CAT procedure using virtual anthropomorphic phantoms2020 - 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.Artigo IPEN-doc 25751 Conversion Coefficients of equivalent and effective doses in terms of air kerma for computational scenarios of Total Body Irradiation in lying-down patients2019 - CUNHA, J.S.; SANTOS, W.S.; CARVALHO JUNIOR, A.B.This study aimed to calculate the Conversion Coefficients (CC) of Equivalent and Effective doses by air kerma considering Total Body Irradiation scenarios with Varian linear accelerator with photon beams energy of 4, 6, 10, 15, 18, and 25 MV. The simulations were performed in the MCNPX code and the University of Florida (UF) phantoms were used to represent exposed lying down adult patients in the AP, PA, RLAT, and LLAT irradiation geometries. Lead attenuators were inserted in the scenarios for the preservation of organs of risk and their contribution were analyzed for CC. For most counts, the statistical uncertainty was approximately 5%. For the gonads, CC values for the male phantom decreased with the increase of energy in the AP geometry, which did not occur for the female phantom. As the beam becomes more penetrating, the ovary absorbs more energy because of its internal position. Considering the lung, an organ of risk in TBI, the insertion of the attenuators in the scenarios caused the CC values to reduce by more than 30%. For organs and tissues such as skin and male breasts, the attenuators caused the dose to increase. As for the active bone marrow, which is the TBI target tissue, it was not possible to obtain a good estimate for CC at 15, 18, and 25 MV due to a limitation of the method used to calculate the dose in the bone areas. Nevertheless, for lower energies the CC values for the marrow were valid.