https://repositorio.ufu.br/handle/123456789/18979 2026-09-24T18:35:06Z 2026-09-24T18:35:06Z https://repositorio.ufu.br/handle/123456789/50147 2026-09-05T06:22:06Z 2026-07-07T00:00:00Z

Title: Simulação Monte Carlo em irradiação de corpo inteiro: validação de feixe clínico e avaliação dosimétrica em objetos antropomórficos virtuais adulto e infantil Abstract: Radiotherapy plays a pivotal role in the management of cancer and is indicated for a substantial proportion of patients, with curative, adjuvant, or palliative intent. Among its applications, Total Body Irradiation (TBI) stands out as an integral component of conditioning regimens for bone marrow transplantation, especially in patients with acute myeloid leukemia (AML). However, TBI presents specific dosimetric challenges related to the large extent of the irradiated volume, anatomical heterogeneity, and the need for dose homogeneity throughout the patient's body. In this context, the present study aimed to develop and validate, using the Monte Carlo (MC) method with the MCNP 6.3 code, a computational model of the 6 MV clinical beam from a VersaHD linear accelerator and apply it to the simulation of a TBI scenario with a long source to-surface distance (SSD). The dose distribution in adult and pediatric anthropomorphic MRCP mesh phantoms of both sexes, developed by the ICRP, was evaluated. The modeling included the implementation of a phase-space-based virtual source already described in the literature, as well as the geometric representation of the collimation system (MLC and backup jaws). Model validation was performed by comparing simulated results with experimental data, using percentage-depth dose (PDD) curves, beam profiles at different depths, and the TPR20,10 beam quality index. Agreement within clinically acceptable limits was observed, with percentage differences on the order of 3% for the reference field, 10 × 10 cm². After beam validation, the model was applied to the simulation of the TBI scenario, allowing the estimation of the absorbed dose in organs at risk and the comparison of the dose distribution between pediatric and adult models of the MRCP phantoms. The results show variations associated with anatomical and dimensional differences between the phantom objects, highlighting the importance of individualized approaches in dose estimation for each patient. It is concluded that the developed model demonstrated dosimetric robustness and clinical applicability, proving to be a reliable tool for dose distribution analysis in TBI and contributing to the improvement of the characterization of radiotherapy beams in complex scenarios.

2026-07-07T00:00:00Z https://repositorio.ufu.br/handle/123456789/49507 2026-08-17T16:28:06Z 2026-07-15T00:00:00Z

Title: Modelagem e validação Monte Carlo do acelerador Halcyon™ para caracterização do Beam Stopper Abstract: The Varian Halcyon™ linear accelerator, featuring an O-Ring architecture and fully jawless collimation by a dual-layer multileaf collimator, has a high-atomic-number beam stopper positioned opposite the isocenter, whose radiation-protection function still requires quantitative characterization. This work aimed to develop, validate, and apply a geometric model of the Halcyon™ treatment head in the MCNP6.2 radiation transport code, based on the stochastic Monte Carlo method, in order to characterize the performance of the beam stopper in structural shielding and in patient dose. The model, comprising the target, the primary collimator, the dual-layer multileaf collimator, and the lead–antimony alloy beam stopper (11.34 g/cm³), was validated against the clinical commissioning data of the Eclipse treatment planning system. The gamma index was used, with the 3%/3 mm and 2%/2 mm criteria, on percentage depth-dose curves and lateral profiles for seven field sizes, from 2 × 2 to 28 × 28 cm². The validation showed satisfactory agreement between the model and the clinical data, with passing rates above 95% under the 3%/3 mm criterion in most configurations and deviations expected only for the smallest field sizes. Once the model was validated, the attenuation of the primary beam by the beam stopper and its contribution to the primary barrier of the bunker were estimated. A real clinical prostate volumetric modulated arc therapy (VMAT) plan was then reconstructed from the accelerator's trajectory log and the ICRP 145 AM anthropomorphic phantom, in order to quantify the peripheral and surface dose associated with backscatter from the component. The beam stopper proved to be an effective attenuator of the primary beam transmitted along the central axis, equivalent to 2.58–2.98 tenth-value layers (TVL). Its effect on patient dose was found to be real but clinically negligible: below 1.4%, restricted to distal cortical bone structures outside the treatment field, corresponding to a small increase in dose due to backscatter and with no statistical significance in the irradiated regions. It is concluded that the beam stopper acts essentially as a shielding element, with trivial influence on the therapeutic dose, and that the developed model constitutes a validated tool for dosimetric and radiation-protection studies in accelerators with an architecture similar to that of the Halcyon™.

2026-07-15T00:00:00Z https://repositorio.ufu.br/handle/123456789/49159 2026-07-30T06:26:09Z 2025-12-16T00:00:00Z

Title: Desenvolvimento e aprimoramento de Phantoms antropomórficos mamográficos Abstract: Considering the high cost, limited accessibility, and low reproducibility of commercially available mammographic phantoms, several studies have proposed alternative models using more accessible materials, such as the Maria Phantom. This model was originally designed to simulate different breast densities using layers of gel paraffin and PVC (polyvinyl chloride) films arranged randomly. However, the plates deformed over time and varied in size, resulting in irregular edges during image acquisition. To address these limitations, this study aimed to improve the Maria Phantom by reducing layer deformation using beeswax, standardizing plate geometry, and minimizing irregularities using 3D-printed molds. The new model was named “BeeMamma” Phantom. Gel paraffin and beeswax were tested as adipose-equivalent materials, with beeswax demonstrating greater durability, ease of handling, and radiological behavior like adipose tissue and gel paraffin. Plates representing different breast densities were fabricated by varying PVC film quantities, and additional plates containing simulated microcalcifications and 3D-printed nodules were incorporated. BeeMamma Phantom images were acquired on different mammography systems and analyzed using texture descriptors, including the 14 Haralick features, Skewness, and Kurtosis. Initial analyses showed that Beeswax presents radiographic characteristics comparable to adipose tissue and offers improved structural stability during manufacturing and storage. Attribute analysis indicated that BeeMamma Phantom reproduces breast tissues of varying densities effectively, preserving the textural characteristics observed in the Maria Phantom while overcoming limitations related to shape irregularities, deformation and handling difficulties. Furthermore, BeeMamma Phantom exhibited texture patterns like those of real mammographic images, supporting its suitability for testing new image-processing techniques and validating CAD and CADx schemes.

2025-12-16T00:00:00Z https://repositorio.ufu.br/handle/123456789/49123 2026-07-28T06:21:53Z 2026-07-20T00:00:00Z

Title: Marcapasso na radioterapia mamária: caracterização computacional das alterações dosimétricas Abstract: Cancer is one of the leading causes of death worldwide, and breast cancer is the second most frequent type and the most common among women. Population aging and unhealthy lifestyle habits contribute to the development of cancer and cardiovascular diseases (CVD), which often make the implantation of a cardiac electronic device necessary. Thus, patients with breast cancer and an implanted pacemaker may undergo radiotherapy, which is one of the treatment modalities for breast cancer. It is well established that pacemakers contain radiation-sensitive components and, because they are composed of metallic structures, may generate radiation scattering when directly exposed to the primary treatment beam. Therefore, the present study aims to analyze the dosimetric influence of the pacemaker on dose coverage in the breast, as well as to determine the absorbed dose by the device under the scenarios investigated. The Monte Carlo code TOPAS was used to simulate a breast cancer radiotherapy scenario with tangential fields on a TrueBeam linear accelerator using a 6 MV photon beam. The TET2DICOM software was used to convert the female mesh-type anthropomorphic reference phantom (MRCP) from ICRP Publication 145 into a set of DICOM images for implementation in TOPAS. Dose–volume histograms were generated, and the main dose metrics were extracted using the 3D Slicer software. The results showed that the presence of the pacemaker has a negligible impact on dose delivery to the treatment target volume. The prescription dose, D95%, was slightly reduced from 47.64 to 47.44 Gy, while the mean absorbed dose to the breast remained unchanged. Collimating the pacemaker as a strategy to reduce the absorbed dose to the device decreased its dose from 26.04 to 1.58 Gy; however, it also reduced breast dose coverage (D95% = 17.56 Gy), making this approach of limited clinical effectiveness. Advanced techniques, such as pacemaker-sparing Volumetric Modulated Arc Therapy (VMAT), should be investigated in future studies.

2026-07-20T00:00:00Z