[Show abstract][Hide abstract] ABSTRACT: The combination of radiotherapy treatments and breast reconstruction, using temporary tissue expanders, generates several concerns due to the presence of a magnetic valve inside the radiation field. The objective of this work is to evaluate a radiotherapy treatment planning for a patient using a tissue expander. Isodose curve maps, obtained using radiochromic films, were compared to the ones calculated with two different dose calculation algorithms of the Eclipse radiotherapy Treatment Planning System (TPS), considering the presence or absence of the heterogeneity. The TPS calculation considering the presence of the heterogeneity shows changes around 5% in the isodose curves when they were compared with the calculation without heterogeneity correction. This calculation did not take in account the real density value of the heterogeneity. This limitation was quantified to be around 10% in comparison with the TPS calculation and experimental measurements using the radiochromic film. These results show that the magnetic valve should be taken in account in dose calculations of the TPS. With respect to the AAA and Pencil Beam Convolution algorithms, when the calculation is compared with the real distribution, AAA presents a distribution more similar to experimental dose distribution.
[Show abstract][Hide abstract] ABSTRACT: A geometric acrylic phantom was designed and built for dose distribution verification in Stereotactic Radiosurgery. Acrylic objects representing the tumor tissue, (target volume (TV)), and the organ at risk (OAR), the brainstem, were inserted inside this phantom. The TV is represented by two semi-spheres of acrylic with a diameter of 13.0 mm, both having a central cavity for accommodation of a TLD-100 detector and a small radiochromic Gafchromic EBT film. The OAR is represented by the two parts of a 38.0 mm length acrylic cylinder with a diameter 18.0 mm and cavities along the cylinder central axis able to accommodate 5 TLD - 100 detectors and another of EBT film between the two cylinder parts. This experimental setup was submitted to a radiosurgical treatment, after which the TL dosimeters were evaluated and their responses were compared with the planned dose values. The radiochromic EBT films showed the dose distributions. The linear accelerator used was a Varian 2300 C/D, generating a 6 MV photon beam. The investigated phantom system was able to check the accuracy of dose delivery to predetermined points and the dose distribution due to stereotactic radiosurgery treatments and proved to be a good tool for quality control in these situations.
[Show abstract][Hide abstract] ABSTRACT: Clinical studies have shown antineoplastic effectiveness of monoclonal antibodies (MAbs) against EGFR for different indications. Several MAbs directed to EGFR were developed recently, such as matuzumab, but there is still lack of information on preclinical data on its combination with chemo-radiation. Thus, the present study intended to examine the molecular pathways triggered by matuzumab alone or associated to chemo-radiotherapy in gynecological cell lines and its impact on cell growth and signaling.
Combination of matuzumab with radiation and cisplatin did not enhance its cytostatic effects on A431, Caski and C33A cells (high, intermediate and low EGFR expression, respectively) in clonogenic assays, when compared to controls. The lack of effect was mediated by persistent signaling through EGFR due to its impaired degradation. In spite of the fact that matuzumab inhibited phosphorylation of EGFR, it had no effect upon cell viability. To analyze which downstream molecules would be involved in the EGFR signaling in the presence of matuzumab, we have tested it in combination with either PD98059 (MAPK inhibitor), or LY294002 (PI3K inhibitor). Matuzumab exhibited a synergic effect with LY294002, leading to a reduction of Akt phosphorylation that was followed by a decrease in A431 and Caski cells survival. The combination of PD98059 and matuzumab did not show the same effect suggesting that PI3K is an important effector of EGFR signaling in matuzumab-treated cells. Nonetheless, matuzumab induced ADCC in Caski cells, but not in the C33A cell line, suggesting that its potential therapeutic effects in vitro are indeed dependent on EGFR expression.
Matuzumab combined with chemoradiation did not induce cytotoxic effects on gynecological cancer cell lines in vitro, most likely due to impaired EGFR degradation. However, a combination of matuzumab and PI3K inhibitor synergistically inhibited pAkt and cell survival, suggesting that the use of PI3K/Akt inhibitors could overcome intrinsic resistance to matuzumab in vitro. Altogether, data presented here can pave the way to a rational design of clinical strategies in patients with resistant profile to anti-EGFR inhibitors based on combination therapy.
[Show abstract][Hide abstract] ABSTRACT: This paper presents the application of a computational methodology for optimizing the conversion of medical tomographic images in voxel anthropomorphic models for simulation of radiation transport using the MCNP code. A computational system was developed for digital image processing that compresses the information from the DICOM medical image before it is converted to the Scan2MCNP software input file for optimization of the image data. In order to validate the computational methodology, a radiosurgery treatment simulation was performed using the Alderson Rando phantom and the acquisition of DICOM images was performed. The simulation results were compared with data obtained with the BrainLab planning system. The comparison showed good agreement for three orthogonal treatment beams of (60)Co gamma radiation. The percentage differences were 3.07%, 0.77% and 6.15% for axial, coronal and sagital projections, respectively.
Full-text · Article · Sep 2011 · Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine
[Show abstract][Hide abstract] ABSTRACT: The Brazilian Institute of Radiation Protection and Dosimetry (IRD/CNEN) carried out quality assurance regulatory audits in Brazilian radiotherapy facilities from 1995 to 2007. In this work, the set of data collected from 195 radiotherapy facilities that use high-energy photon beams are analyzed. They include results from audits in linear electron accelerators and/or Co-60 units. The inspectors of IRD/CNEN performed the dosimetry of high-energy radiotherapy photon beams according to the IAEA dosimetry protocols TRS 277 and TRS 398, and the values of measurements were compared to stated values. Other aspects of radiological protection were checked during on-site audits such as calibration certification of clinical dosimeters and portable monitors, existence and use of check source, use of barometer and thermometer, individual dose registry and training of staff. It was verified that no check source was available in 38% of the visited facilities; the training of personnel was not adequate in 9% of the facilities and the registry of accumulated individual doses was not being done in 6% of the facilities. Measurements of absorbed dose have indicated deviations in the range ± 3% for 67.6% of the cobalt-60 units and 79.6% of medical linear accelerators; 18.5% of Co-60 irradiators and 9.6% of linear accelerators presented deviations in the range 3% < δ ≤ 5%. Finally, 13.9% of Co-60 facilities and 10.8% of linear accelerator facilities presented dosimetry deviations above 5%. The effort in dosimetric quality control performed by IRD/CNEN audits has yielded positive changes that make radiation treatment facilities more reliable.
Full-text · Article · Jan 2011 · Journal of Applied Clinical Medical Physics
[Show abstract][Hide abstract] ABSTRACT: Calibrated survey meters from the Neutron Laboratory of the Instituto de Radioproteção e Dosimetria (IRD) were used to determine the ambient dose-equivalent rate in a 15 MV linear accelerator treatment room at the Instituto Nacional do Câncer (INCa). Three different models of neutron survey meters were calibrated using four neutron radionuclide neutron sources: 241AmBe(α,n), 252Cf(f,n), heavy-water moderated 252Cf(f,n), and 238PuBe(α,n). All neutron sources were standardized in a Manganese Sulphate Bath (MSB) absolute primary system. The response of each of these instruments was compared with reference values of ambient dose-equivalent rate. The results demonstrate the complexity of making measurements in the mixed neutron/photon field produced in electron linear accelerator radiotherapy treatment rooms.
No preview · Article · Dec 2010 · Radiation Measurements
[Show abstract][Hide abstract] ABSTRACT: In the radiotherapy treatment planning of a lesion located in the head region with small field radiation beams, the heterogeneity corrections play an important role. In this work, we investigated the influence of a bony heterogeneity on dose profile inside a soft tissue phantom containing a bony material. PDD curves were obtained by simulation using the Monte Carlo code EGSnrc and employing Eclipse(R) treatment planning system algorithms (Batho, Modified Batho, Equivalent TAR and Anisotropic Analytic Algorithm) for a 15 MV photon beam and field sizes of 2x2 and 10x10 cm(2). The Equivalent TAR method exhibited better agreement with Monte Carlo simulations for the 2x2 cm(2) field size. The magnitude of the effect on PDD due to the bony heterogeneity for 1x1, 2x2 and 10x10 cm(2) field sizes increases to 10, 5 and 3%, respectively.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study is to investigate the influence of lung heterogeneity inside a soft tissue phantom on percentage depth dose (PDD). PDD curves were obtained experimentally using LiF:Mg,Ti (TLD-100) thermoluminescent detectors and applying Eclipse treatment planning system algorithms Batho, modified Batho (M-Batho or BMod), equivalent TAR (E-TAR or EQTAR), and anisotropic analytical algorithm (AAA) for a 15 MV photon beam and field sizes of 1 x 1, 2 x 2, 5 x 5, and 10 x 10 cm 2 . Monte Carlo simulations were performed using the DOSRZnrc user code of EGSnrc. The experimental results agree with Monte Carlo simulations for all irradiation field sizes. Comparisons with Monte Carlo calculations show that the AAA algorithm provides the best simulations of PDD curves for all field sizes investigated. However, even this algorithm cannot accurately predict PDD values in the lung for field sizes of 1 x 1 and 2 x 2 cm 2 . An overdosage in the lung of about 40% and 20% is calculated by the AAA algorithm close to the interface soft tissue/lung for 1 x 1 and 2 x 2 cm 2 field sizes, respectively. It was demonstrated that differences of 100% between Monte Carlo results and the algorithms Batho, modified Batho, and equivalent TAR responses may exist inside the lung region for the 1 x 1 cm 2 field.
Full-text · Article · Jan 2010 · Journal of Applied Clinical Medical Physics
[Show abstract][Hide abstract] ABSTRACT: In this work we determined PDD curves and dose profiles for narrow beams produced by a cobalt-60 therapy unity aimed to be
used in radiosurgery through the cone beam technique. PDD curves were obtained by three techniques, namely diode dosimetry,
ionization chamber dosimetry and radiochromic film dosimetry. The results present a good agreement. The dose profiles obtained
for cobalt-60 were compared to those ones generated by a linac 2300C accelerator. For a same cone collimator, the area of
treatment generated by cobalt -60 beam was smaller. The mean responsible for this situation is the wider penumbra present
by the cobalt-60 beam.
[Show abstract][Hide abstract] ABSTRACT: OBJETIVO: O objetivo deste trabalho foi desenvolver um sistema dosimétrico termoluminescente capaz de avaliar as doses administradas ao reto de pacientes submetidas a braquiterapia de alta taxa de dose para o tratamento do câncer do colo uterino. MATERIAIS E MÉTODOS: O material termoluminescente utilizado para a avaliação da dose no reto foi o LiF:Mg,Ti,Na na forma de pó. O pó foi separado em pequenas porções de 34 mg, que foram acomodadas em um tubo capilar. Este tubo foi colocado em uma sonda retal, que era introduzida no reto da paciente. RESULTADOS: As doses administradas ao reto de seis pacientes submetidas a braquiterapia de alta taxa de dose para o tratamento do câncer do colo uterino foram avaliadas com dosímetros termoluminescentes e apresentaram boa concordância com os valores planejados, com base em duas radiografias ortogonais da paciente, imagens ântero-posterior e lateral. CONCLUSÃO: O sistema de dosimetria termoluminescente utilizado no presente trabalho é simples e de fácil utilização quando comparado a outros métodos de dosimetria do reto. Ele mostrou-se eficiente na avaliação da dose no reto de pacientes submetidas a braquiterapia de alta taxa de dose para o tratamento do câncer do colo uterino.
[Show abstract][Hide abstract] ABSTRACT: Resumo O presente trabalho apresenta uma caracterização das propriedades físicas do filtro dinâmico do acelerador linear Clinac 2300 CD da Varian Medical Systems, instalado no Instituto Nacional de Câncer (INCA), no Rio de Janeiro. Foram medidos os "fatores filtro dinâmico" para as energias de 6 e 15 MV de fótons, em campos quadrados e retangulares, e comparados com os fatores fornecidos no manual do acelerador e utilizados pelo sistema de planejamento, estando os mesmos em excelente concordância. Também foram medidos os percentuais de dose profunda (PDP) para todos os filtros dinâmicos, posições IN e OUT, nas profundidades de máxima dose, 5 cm, 10 cm e 20 cm, para as energias de 6 e 15 MV de fótons. Observou-se que os "fatores filtro dinâmico" não variam com a profundidade e que os PDP's para o campo aberto são os mesmos para os campos com filtro dinâmico.Os ângulos dos filtros dinâmicos também foram obtidos experimentalmente e comparados com os ângulos nominais do acelerador e do sistema de planejamento. Algumas discrepâncias foram encontradas. Palavras chaves: Aceleradores Lineares, Filtros Dinâmicos, Controle de Qualidade em Radioterapia. Introdução Em certos tratamentos de neoplasias malignas com radioterapia, é muitas vezes necessário interpor entre o feixe de radiação e o paciente, um filtro, que pode ser físico ou virtual. O filtro dinâmico é um filtro não físico que gera distribuições de dose com perfil assimétrico, moldadas pelo movimento de colimadores e ajuste da taxa de dose durante o tratamento. Este método é um caso especial da modulação dinâmica da intensidade de radiação. A base da modalidade Filtro Dinâmico é a tabela de tratamento segmentada (Segmented Treatment Table – STT) que governa a posição dos colimadores em relação ao número de Unidades de Monitor executadas. A STT do filtro dinâmico especifica o movimento dos colimadores em passos iguais como função da dose fracional cumulativa; começando com o campo aberto e movimentando os colimadores até que fiquem na posição final fechados. As tabelas STT estão armazenadas no computador do acelerador para cada energia, tamanho de campo e ângulo do filtro disponíveis. Qualquer tamanho de campo contido dentro dos limites do movimento dos colimadores é possível, simétrico ou assimétrico. Em geral, todo o tratamento com EDW da Varian começa com alguma parcela da dose sendo liberada com um campo aberto. Depois a fração restante da dose é liberada de acordo com o movimento do colimador. A fração exata da dose que é liberada com o campo aberto é uma função da energia, tamanho de campo e ângulo do filtro. Da mesma maneira, a relação entre a posição do colimador e a quantidade de dose liberada é função das mesmas variáveis. O número de Unidades de Monitor liberadas conforme o colimador se movimenta é continuamente ajustado para alcançar a distribuição de dose desejada. A taxa de dose e a velocidade do colimador são também variadas durante o tratamento, de maneira a permitir que o tratamento seja executado no menor tempo possível.