Browsing by Issue Date, starting with "2005-09"
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- 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.
- Eye tracker, binocular vision and oculomotor balance: exploratory studyPublication . Mendanha, Luís; Oliveira, Manuel; Pereira, Leonor MonizWe have analysed the vision direction with the Eye Tracker System ASL-model 504 of individuals with alterations of oculomotor balance or binocular vision, comparing them with individuals without those kinds of alterations. The sample was composed of 40 individuals, men, and women, with ages between 18 and 23. They were distributed as follows: individuals with normal binocular vision (NBV) in binocular and monocular conditions and with convergence insufficiency (CI). Significant differences were found between the studied groups, pointing out that the absence of binocularity, as the existence of convergence insufficiency, entails clearly a quality loss of the visual pursuit.
- Comparing a current-carrying circular wire with polygons of equal perimeter: Magnetic field versus magnetic fluxPublication . Silva, J .P.; Silvestre, António JorgeWe compare the magnetic field at the centre and the self-magnetic flux through a current-carrying circular loop, with those obtained for current-carrying polygons with the same perimeter. As the magnetic field diverges at the position of the wires, we compare the self-fluxes utilizing several regularization procedures. The calculation is best performed utilizing the vector potential, thus highlighting its usefulness in practical applications. Our analysis answers some of the intuition challenges students face when they encounter a related simple textbook example. These results can be applied directly to the determination of mutual inductances in a variety of situations.
- Failure modes and effects analysis (FMEA) applied to two modern radiotherapy centresPublication . Teixeira, Nuno; Cunha, Gilda; Moreno, L.; Pontes, M.; Rosa, M.; Jacob, K.; Cardoso, I.; Ferreiras, P.; Ramalho, M.; Carvoeiras, P.; Galhós, R.FMEA is a quality improvement technique, generally applied to industry, that can provide an efficient, structured approach to assessing interconnected system failures. It is a bottom up analytical process, which identifies process hazards. According to this technique, each potential failure mode in the system is analysed to determine its effect and to classify it according to its severity. The objective is to identify reliability-critical areas in the system for which modifications to the design or maintenance procedures are required to eliminate single point failures and any catastrophic or critical consequences of such failures. Each individual component of the system is considered separately for each of its failure modes. The procedure involves the following steps: 1.Define the system and its required reliability performance. 2.Construct functional block diagrams to define and illustrate how the different sub-systems are interconnected. 3.List the components, identify their failure modes and where available their modal failure rates. 4.Complete a set of FMEA worksheets analysing the effect of each sub-assembly or component failure mode on overall system performance. Severity rankings are then assigned to each failure mode. 5.Review the worksheets to identify the reliability-critical components and make recommendations for design improvements or amendments to maintenance schedules In this work authors are presenting a FMEA study of two recent radiotherapy centres in Lisbon (Centro Oncológico Dra. Natália Chaves and Hospital CUF-Descobertas), where there are two very different radiotherapy equipments: Varian accelerator, VarisVision network and Eclipse TPS (in the first centre) and Elekta accelerator, Impac network and Xio TPS (in the second centre). This study covers a time-period of one year (all the 2004 year), and allows some very interesting conclusions related to the way the equipment behaves and how one may prevent some problems.
- Ionometric and fricke electron and gamma dosimetry for the implementation of waste water treatment by radiation in PortugalPublication . Ferreira, P.; Jacob, K.; Rosat, M.; Galhós, R.; Serrai, F.; Oliveira, S.; Teixeira, Nuno; Ramalho, M.Application of radiation as an efficient process to reduce the microbial levels in materials (food, environmental, health care products). Irradiation of organic and inorganic compounds with electron and gamma rays can modify the micro organisms, depending on the energy, dose rate, and others variables related to the irradiation conditions. Anthropogenic sources have been responsible for introducing high levels of chemical elements and compounds into the environment, many of this through the industrial waste waters. This is an issue of global concern, with potential impact on human health and the environment. IAEA recognizes the potentiality of radiation technology to clean up waste discharges, and since 2003 IAEA participate in this project. Although this is a multidisciplinary project, by the physical point of view the main objective is to characterize the most efficient electron (by intercomparison with gamma) beam, obtaining the better irradiation geometry, to implement waste water (originated in hospitals, food industry ...) treatments. Until now, we've characterized electron beams with Ionometric and fricke dosimetry at non-standard irradiation conditions, in commercial Linacs for radiotherapy purposes. We used a Varian Clinac 2100 CD, with the special TBI ETRAY conditions and nominal dose rate of 1000 UM/min, and an Elekta Digital Precise with nominal dose rate of 400 UM/min. The better dose rates obtained in water were approximately equal to 1.4 kGy/h and 0.7 kGy/h, respectively. The impact of the radiation has been studied microbiologically, toxicologically and chemically, and the evaluation between this kind of radiation and cobalt gamma radiation is also carried out at the same time. The results obtained until know and the continuous support of the IAEA experts in the project, indicates that this project will contribute to a better quality of the Portuguese industrial or hospital complexes, minimising the impact of pollutants on the environment.
- Accuracy of polls in PortugalPublication . Belo, AntónioThis study has a vast analysis, studying almost all the pre-electoral polls published or issued in Portugal in the month previous to each of the elections, since 1991 until the last one that took place in February 2005. The accuracy measures I used were adapted from the study carried out by Frederick Mosteller in the report to the Committee on Analysis of Pre-election Polls, regarding the USA elections of 1948.
- The body in advertising and the consumersPublication . Pereira, Francisco José Costa; Verissimo, JorgeAdvertising is a mass communication, where, sometimes, beautiful people try to persuade consumers to buy or to do something, because our society places a very high premium on physical attractiveness and tends to assume that what is beautiful is good. In this away the physically attractive source functions as a cue that facilitates information processing by directing consumers' attention to relevant stimuli, which gives rise to positive feelings, (Solomon, Bamossy and Askegaard, 1999). The person's satisfaction with the physical image it presents to others is affected by the proximity that image corresponds to the image valued by his culture, because each culture develops their ideals of beauty that may include physical features as well as clothing styles, among others.
- Image and color recognition using amorphous silicon p-i-n photodiodesPublication . Louro, Paula; Vieira, Manuela; Fantoni, Alessandro; Fernandes, Miguel; Carvalho, C. N.; Lavareda, G.Large area hydrogenated amorphous silicon single and stacked p-i-n structures with low conductivity doped layers are proposed as monochrome and color image sensors. The layers of the structures are based on amorphous silicon alloys (a-Si(x)C(1-x):H). The current-voltage characteristics and the spectral sensitivity under different bias conditions are analyzed. The output characteristics are evaluated under different read-out voltages and scanner wavelengths. To extract information on image shape, intensity and color, a modulated light beam scans the sensor active area at three appropriate bias voltages and the photoresponse in each scanning position ("sub-pixel") is recorded. The investigation of the sensor output under different scanner wavelengths and varying electrical bias reveals that the response can be tuned, thus enabling color separation. The operation of the sensor is exemplified and supported by a numerical simulation.
- Enhanced short wavelength response in laser-scanned-photodiode image sensor using an a-SiC : H/a-Si : H tandem structurePublication . Fantoni, Alessandro; Louro, Paula; Fernandes, Miguel; Vieira, Manuela; Lavareda, G.; Carvalho, C. N. deWe report in this paper the recent advances we obtained in optimizing a color image sensor based on the laser-scanned-photodiode (LSP) technique. A novel device structure based on a a-SiC:H/a-Si:H pin/pin tandem structure has been tested for a proper color separation process that takes advantage on the different filtering properties due to the different light penetration depth at different wavelengths a-SM and a-SiC:H. While the green and the red images give, in comparison with previous tested structures, a weak response, this structure shows a very good recognition of blue color under reverse bias, leaving a good margin for future device optimization in order to achieve a complete and satisfactory RGB image mapping. Experimental results about the spectral collection efficiency are presented and discussed from the point of view of the color sensor applications. The physics behind the device functioning is explained by recurring to a numerical simulation of the internal electrical configuration of the device.
- A two terminal optical signal and image processing p-i-n/p-i-n image and colour sensorPublication . Vieira, Manuela; Fernandes, Miguel; Louro, Paula; Fantoni, Alessandro; Lavareda, G.; Carvalho, C. N. de; Vygranenko, YuriA two terminal optically addressed image processing device based on two stacked sensing/switching p-i-n a-SiC:H diodes is presented. The charge packets are injected optically into the p-i-n sensing photodiode and confined at the illuminated regions changing locally the electrical field profile across the p-i-n switching diode. A red scanner is used for charge readout. The various design parameters and addressing architecture trade-offs are discussed. The influence on the transfer functions of an a-SiC:H sensing absorber optimized for red transmittance and blue collection or of a floating anode in between is analysed. Results show that the thin a-SiC:H sensing absorber confines the readout to the switching diode and filters the light allowing full colour detection at two appropriated voltages. When the floating anode is used the spectral response broadens, allowing B&W image recognition with improved light-to-dark sensitivity. A physical model supports the image and colour recognition process.