AvaliaÃÃo dos parÃmetros dosimÃtricos em feixes de FÃtons de Radioterapia usando fototransistor SMT
AUTOR(ES)
Jonas Oliveira da Silva
DATA DE PUBLICAÇÃO
2008
RESUMO
One of the biggest challenges in radiotherapy dosimetry is to certify that the prescribed dose is given to the patient. For this, it is necessary to use small detectors to evaluate the beam parameters. Current dosimetry is realized with detectors that highlight problems: high cost, difficulty in handling, absence of real time readout, complex and delayed obtention process of dose. Thus, an alternative system is proposed applying small detectors, based on semiconductor technology. In this work, the OP520Â phototransistor was proposed to evaluate the dose and some dosimetric parameters from a linear 6 MV beams quality accelerator. First, the phototransistor characterization was carried out in the laboratory and at the hospital, which was placed in a plastic phantom. An electrometer, developed at the laboratory, was connected to a detector and to a instrumentation computer, to complete the dosimetric system. To obtain the real time readouts, a computer software was developed. It was noted that when the behavior of the detector is known in relation to the accumulated dose, it is possible to find the factor that is necessary to estimate the phototransistor dose. The results showed that the phototransistor accumulated dose measurements are within the Â5% required in international protocols. After this, the device was used in the linear accelerator to evaluate its linearity response with the accumulated dose, this showed correlation coefficient responses larger than 0.95. However, the results showed that the device presents dose rate dependence and high angular dependence. In the dosimetric parameter evaluation, the field factor measurements with the phototransistor showed good agreement with ones obtained with the Markus chamber, which was used as standard dosimeter. The dose profiles were measured scanning the radiation fields at 5.0 mm steps, which showed that the OP520 phototransistor presents high spatial resolution. In the depth measurements, the OP520 phototransistor describes the build-up region well, in spite of its loss of sensitivity at profound depths; it presents lower response than the ionization chamber
ASSUNTO(S)
engenharia nuclear x-rays dosimetria radioterapia radiotherapy fototransistor dosimetry raios-x phototransistor
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