Browsing by Author "Teixeira, Nuno"
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- Alternative regimens for prostate cancer treatment using radiation therapyPublication . Oliveira, S. M.; Teixeira, Nuno; Fernandes, Lisete; Brás, S.; Serra, F.Purpose/Objective: The purpose of this work was to determine biologically equivalent alternative regimens for the treatment of prostate cancer using External Beam Radiotherapy (EBRT) and Low Dose-Rate Brachytherapy (LDRBT) with 125I implants and to evaluate the sensitivity of these regimens to different sets of radiobiological parameters of the Linear-Quadratic (LQ) model.
- Alternative regimens for treating prostate cancer using equivalent uniform dose and Monte Carlo methodsPublication . Oliveira, Susana; Rosmanets, Yuriy; Teles, Pedro; Fernandes, Lisete; Teixeira, Nuno; Vaz, PedroIntroduction - Conventional radiotherapy treatments are administrated with 2 Gy external beam radiotherapy (EBRT) fractions. It has been postulated that prostate cancer would respond to radiotherapy as a slowly proliferating late-responding normal tissue, benefiting from hypo-fractionated regimens. Highly conformed brachytherapy is a treatment option either alone or combined with EBRT. Purpose - To identify alternative radiotherapy regimens for treating prostate cancer using EBRT and low dose-rate brachytherapy (LDRBT) with 125I implants, biologically equivalent to conventional treatments in terms of uniform equivalent dose (EUD). Materials and methods - The EUD concept was used, together with Monte Carlo (MC) methods. Two voxel phantoms were segmented from the computed tomography of patients to obtain the energy deposition derived from the MC simulations of EBRT and LDRBT treatments on a voxel-by-voxel basis. The energy deposition was converted in EUD. Equivalent regimens to EUDs of 72 Gy, 80 Gy, 90 Gy, and 100 Gy were determined for increasing fractions of 1.8–5.0 Gy and amounts of LDRBT from 0 Gy (EBRT exclusive) to 145 Gy. The resulting EUD for rectum was also evaluated. Results - Alternative schemes equivalent, in terms of EUD, were obtained. For example, it is equivalent to an EUD of 72 Gy, 38 × 2 Gy, 20 × 3 Gy or 9 × 5 Gy of EBRT, or 6 × 5 Gy of EBRT plus 50 Gy of LDRBT. The rectum benefits of higher amounts of LDRBT for EBRT fractionations <2.5 Gy and larger fractions for LDRBT dose <50 Gy. Conclusion - Alternative regimens for the treatment of prostate cancer with EBRT and LDRBT are proposed. The rational for the use of brachytherapy becomes less relevant with the increasing therapeutic ratio achieved with hypo-fractionated EBRT.
- Assesing multileaf collimator effect on the build-up region using Monte Carlo methodPublication . Zarza-Moreno, M.; Teixeira, Nuno; Jesus, A. P.; Mora, G.Previous Monte Carlo studies have investigated the multileaf collimator (MLC) contribution to the build-up region for fields in which the MLC leaves were fully blocking the openings defined by the collimation jaws. In the present work, we investigate the same effect but for symmetric and asymmetric MLC defined field sizes (2×2, 4×4, 10×10 and 3×7 cm2). A Varian 2100C/D accelerator with 120-leaf MLC is accurately modeled fora6MVphoton beam using the BEAMnrc/EGSnrc code. Our results indicate that particles scattered from accelerator head and MLC are responsible for the increase of about 7% on the surface dose when comparing 2×2 and 10×10 cm2 fields. We found that the MLC contribution to the total build-up dose is about 2% for the 2×2 cm2 field and less than 1% for the largest fields.
- Comparação de diferentes técnicas de irradiação de mama em radioterapia com recurso a acelerador linear em modo de fotõesPublication . Borges, C.; Cunha, Gilda; Teixeira, NunoRESUMO: Introdução – A Radioterapia (RT) é uma abordagem terapêutica para tratamento de neoplasia de mama. Contudo, diferentes técnicas de irradiação (TI) podem ser usadas. Objetivos – Comparar 4 TI, considerando a irradiação dos volumes alvo (PTV) e dos órgãos de risco (OAR). Metodologia – Selecionaram-se 7 pacientes com indicação para RT de mama esquerda. Sobre tomografia computorizada foram feitos os contornos do PTV e dos OAR. Foram calculadas 4 planimetrias/paciente para as TI: conformacional externa (EBRT), intensidade modulada com 2 (IMRT2) e 5 campos (IMRT5) e arco dinâmico (DART). Resultados – Histogramas de dose volume foram comparados para todas as TI usando o software de análise estatística, IBM SPSS v20. Com IMRT5 e DART, os OAR recebem mais doses baixas. No entanto, IMRT5 apresenta melhores índices de conformidade e homogeneidade para o PTV. Conclusões – IMRT5 apresenta o melhor índice de conformidade; EBRT e IMRT2 apresentam melhores resultados que DART. Há d.e.s entre as TI, sobretudo em doses mais baixas nos OAR.
- Comparison of different breast planning techniques and algorithms for radiation therapy treatmentPublication . Borges, C.; Cunha, Gilda; Monteiro-Grillo, I.; Vaz, P.; Teixeira, NunoThis work aims at investigating the impact of treating breast cancer using different radiation therapy (RT) techniques – forwardly-planned intensity-modulated, f-IMRT, inversely-planned IMRT and dynamic conformal arc (DCART) RT – and their effects on the whole-breast irradiation and in the undesirable irradiation of the surrounding healthy tissues. Two algorithms of iPlan BrainLAB treatment planning system were compared: Pencil Beam Convolution (PBC) and commercial Monte Carlo (iMC). Seven left-sided breast patients submitted to breast-conserving surgery were enrolled in the study. For each patient, four RT techniques – f-IMRT, IMRT using 2-fields and 5-fields (IMRT2 and IMRT5, respectively) and DCART – were applied. The dose distributions in the planned target volume (PTV) and the dose to the organs at risk (OAR) were compared analyzing dose–volume histograms; further statistical analysis was performed using IBM SPSS v20 software. For PBC, all techniques provided adequate coverage of the PTV. However, statistically significant dose differences were observed between the techniques, in the PTV, OAR and also in the pattern of dose distribution spreading into normal tissues. IMRT5 and DCART spread low doses into greater volumes of normal tissue, right breast, right lung and heart than tangential techniques. However, IMRT5 plans improved distributions for the PTV, exhibiting better conformity and homogeneity in target and reduced high dose percentages in ipsilateral OAR. DCART did not present advantages over any of the techniques investigated. Differences were also found comparing the calculation algorithms: PBC estimated higher doses for the PTV, ipsilateral lung and heart than the iMC algorithm predicted.
- Controlo da qualidade dosimétrico no serviço de radioterapia do Hospital CUF Descobertas (HCD): importância do controlo da qualidade do sector da física e resultados da auditoria ESTRO-EQUALPublication . Jacob, Katia; Rosa, Maria João; Ferreira, Paulo; Oliveira, Susana; Sousa, Mónica; Fernandes, Paulo; Parafita, R.; Teixeira, Nuno; Ramalho, Miguel; Rodrigues, RuiA calibração e o controlo da qualidade de um acelerador linear são passos muito importantes num serviço de Radioterapia, para garantir a qualidade dos tratamentos prestados. O sector da Física da Unidade de Radioterapia do Hospital Cuf Descobertas implementou um rigoroso Programa de controlo de qualidade ao equipamento produtor de radiação e aos equipamentos medidores de radiação, de acordo com o Dec-Lei 180/2002 e com os protocolos internacionais. Para tal, foram implementados procedimentos, criadas folhas de cálculo, instruções de trabalho e impressos. Foram ainda implementados testes aos equipamentos com periodicidade definida: controlo de qualidade diário e controlo de qualidade após intervenções (manutenções preventivas e correctivas). No decorrer do ano de 2005, o sector da Física colaborou activamente com toda a equipa da Radioterapia na implementação da Norma ISO 9001:2000 no serviço, contribuindo com o seu know how na implementação desta, numa área tão importante como a da garantia da qualidade dos feixes de radiação e das respectivas calibrações em dose. Numa procura de melhoria contínua da qualidade dos serviços prestados aos pacientes, decorre ainda uma auditoria externa da EQUAL-ESTRO*, intercomparação postal com dosímetros termoluminescentes. A qualidade dos feixes de energias utilizados diariamente é analisada, tanto ao nível das calibrações absolutas de cada um dos feixes de fotões e de electrões, como ao nível dos cálculos de dose obtidos com o sistema de planimetria XiO da CMS. Os resultados das duas primeiras fases da intercomparação, relativa aos dois feixes de fotões de 6 MV e 15 MV e feixes de electrões de 4 MeV, 8 MeV e 12 MeV, foram considerados pela EQUAL-ESTRO num nível óptimo (desvio máximo na dose medida em relação à dose de referência |d| ≤ 3%).
- Dose and image quality in computed tomography: an overview of Portuguese dataPublication . Coutinho, Ana Margarida; Teixeira, Nuno; Trindade, Hugo; Coutinho, GuilhermeComputed Tomography exams expose patients to higher dose levels than most exams in radiology and the number of CT exams is increasing year after year in Portugal. In 2009 were performed 1.1 million CT exams and later in 2014, there were 1.6 million. This study aims to analyze dose and image quality data gathered from 180 distinct computed tomography systems, which represents 350 quality assurance interventions done in Portuguese national health units (mainland and islands) between 2014 and 2017. In the quality assurance interventions, a Catphan® 500 phantom was aligned in the center of the gantry and irradiated, for analysis of six parameters: CT numbers, slice thickness, low and high contrast resolution, uniformity and noise. Afterwards, an ionization chamber (Raysafe Xi CT sensor) was placed in the interior of a PMMA (polymethylmethacrylate) phantom and the Computed Tomography Dose Index (CTDI) was measured. Data analysis was performed using IBM SPSS v.22.0. In order to verify the CT numbers, four materials with different densities were analyzed and the mean CT numbers obtained were: -980 HU (Air), -943 HU (Teflon), -115 HU (Acrylic) and -99 HU (LDPE). The high contrast resolution values were determined for X-ray energies in a range of 80 kV to 100 kV at 200 mA and the mean spatial resolution obtained was 8 lp/cm with a gap size of 0,063 cm. When increasing the voltage to 130-140 kV the mean spatial resolution was 9 lp/cm with a gap size of 0,056 cm. Dose measured in the head and body scan techniques, with a voltage between 80 kV and 100 kV at 100 mA and 10 mm slice thickness was 6 my and 3 mGy, respectively. When increasing the voltage to 130-140 kV the mean values obtained were 23 mGy (head) and 12 mGy (body). These results show that with lower voltage the CTDI is four times lower while keeping an adequate spatial resolution. Adequate CT protocols are very important to ensure safety to all patients, and specifically designed pediatric protocols should be used, once children are more sensitive to the effects of ionizing radiation. It is important to adopt CT exams in order to minimize exposure while providing good diagnostic quality. In this study a comparison between adults and children protocols is made (using international publications like the ones form AAPM - American Association of Physicists in Medicine), using dose and resolution data from the Portuguese equipment.
- Dosimetric considerations from 200 prostate brachytherapy treatments with 1251 according to the real-time planning methodPublication . Teixeira, Nuno; Campos, L.; Carvoeiras, P.; Cunha, Gilda; Varregoso, J.; Valsassina, R.; Pontes, M.; Galhos, R.; Ferreira, P.; Justo, U.Prostate brachytherapy with radioactive seeds is one of the options for prostate cancer treatment. Some dosimetric methods may be used, from the pre-planning to the realtime planning. This study covers 200 patients treated with 12sI radioactive seeds, for a period of time of 4 years. The software used is VariSeed. According to the real-time planning method, the dosimetry is done inside the operating room. The ultrasound probe is inside the rectum of the patient during all the treatment time, and images of the prostate, urethra and rectum are obtained by ultrasound technique. The dosimetry is on realtime, and the source positions in the TPS are exactly the same of the positions inside the prostate. With this technique one may have the values of very important parameters, like Dgo Dgs Vgo Dloo and Vlso for prostate. After one month the patient is submitted to a CT exam, and a new dosimetry is performed, being the contouring done over the new C-I images. With this new dosimetry one may calculate the same parameters already calculated for the real-time planning dosimetry. In this work authors present a statistical analysis (table 1) of the main parameters, obtained either duringthe pre-planning dosimetry or from the CT, and show some very interesting results and conclusions.
- Dosimetric effect by shallow air cavities in high energy electron beamsPublication . Zarza-Moreno, M.; Carreira, P.; Madureira, L.; Miras del Rio, H.; Salguero, F. J.; Leal, A.; Teixeira, Nuno; Jesus, A. P.; Mora, G.This study evaluates the dosimetric impact caused by an air cavity located at 2 mm depth from the top surface in a PMMA phantom irradiated by electron beams produced by a Siemens Primus linear accelerator. A systematic evaluation of the effect related to the cavity area and thickness as well as to the electron beam energy was performed by using Monte Carlo simulations (EGSnrc code), Pencil Beam algorithm and Gafchromic EBT2 films. A home-PMMA phantom with the same geometry as the simulated one was specifically constructed for the measurements. Our results indicate that the presence of the cavity causes an increase (up to 70%) of the dose maximum value as well as a shift forward of the position of the depthedose curve, compared to the homogeneous one. Pronounced dose discontinuities in the regions close to the lateral cavity edges are observed. The shape and magnitude of these discontinuities change with the dimension of the cavity. It is also found that the cavity effect is more pronounced (6%) for the 12 MeV electron beam and the presence of cavities with large thickness and small area introduces more significant variations (up to 70%) on the depthedose curves. Overall, the Gafchromic EBT2 film measurements were found in agreement within 3% with Monte Carlo calculations and predict well the fine details of the dosimetric change near the cavity interface. The Pencil Beam calculations underestimate the dose up to 40% compared to Monte Carlo simulations; in particular for the largest cavity thickness (2.8 cm).
- Dosimetric effect of tissue heterogeneity for 125I prostate implantsPublication . Oliveira, Susana Maria; Teixeira, Nuno; Fernandes, Lisete; Teles, Pedro; Vaz, PedroAim - To use Monte Carlo (MC) together with voxel phantoms to analyze the tissue heterogeneity effect in the dose distributions and equivalent uniform dose (EUD) for (125)I prostate implants. Background - Dose distribution calculations in low dose-rate brachytherapy are based on the dose deposition around a single source in a water phantom. This formalism does not take into account tissue heterogeneities, interseed attenuation, or finite patient dimensions effects. Tissue composition is especially important due to the photoelectric effect. Materials and Methods - The computed tomographies (CT) of two patients with prostate cancer were used to create voxel phantoms for the MC simulations. An elemental composition and density were assigned to each structure. Densities of the prostate, vesicles, rectum and bladder were determined through the CT electronic densities of 100 patients. The same simulations were performed considering the same phantom as pure water. Results were compared via dose-volume histograms and EUD for the prostate and rectum. Results - The mean absorbed doses presented deviations of 3.3-4.0% for the prostate and of 2.3-4.9% for the rectum, when comparing calculations in water with calculations in the heterogeneous phantom. In the calculations in water, the prostate D 90 was overestimated by 2.8-3.9% and the rectum D 0.1cc resulted in dose differences of 6-8%. The EUD resulted in an overestimation of 3.5-3.7% for the prostate and of 7.7-8.3% for the rectum. Conclusions - The deposited dose was consistently overestimated for the simulation in water. In order to increase the accuracy in the determination of dose distributions, especially around the rectum, the introduction of the model-based algorithms is recommended.
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