A dosimetria in vivo é uma ferramenta essencial para programas de garantia de qualidade no campo da radioterapia, sendo um procedimento comumente realizado com TLDs ou diodos. No entanto, um dosímetro que vem em crescente popularidade nos últimos anos é o detector do tipo transistor de efeito de campo de metal-óxido-semicondutor (MOSFET). Os dosímetros MOSFET preenchem todas as características necessárias para realização da dosimetria in vivo, uma vez que possuem tamanho pequeno, boa precisão e viabilidade de medição, além de seu fácil manuseio. No entanto, seu verdadeiro diferencial é permitir a leitura de dose em tempo real, possibilitando intervenção imediata na correção de desvios de parâmetros físicos e na antecipação de pequenas alterações anatômicas no paciente durante um tratamento. Assim, foi proposta a caracterização dosimétrica do detector microMOSFET TN-502RDM-H e a construção de seu respectivo modelo computacional em MCNP6. Os resultados mostraram que o dosímetro MOSFET possui boa reprodutibilidade, boa linearidade e independência energética para feixes de altas energias de fótons e elétrons. Com relação a linearidade, destaca-se o excelente desempenho do detector MOSFET para valores doses acima de 50cGy, tendo apresentado uma precisão de 0,3%. Além disso, foi obtido um fator de calibração único, considerando fótons e elétrons de altas energias, com 2,9% de reprodutibilidade. Também foram constatadas dependências angulares de 4% e 13% para irradiações com e sem a condição de equilíbrio eletrônico, respectivamente. Foi encontrada uma diferença de 8% na resposta entre fótons de baixas energias nas qualidades RQR 3 e RQR 10. Com relação ao modelo computacional, a utilização das técnicas caracterização estrutural de MEV e EDS possibilitaram estimar a geometria e a composição do dispositivo MOSFET. Dos resultados do modelo computacional, ressalta-se a excelente concordância da dependência energética simulada em MCNP6 com a calculada analiticamente e também com a literatura. Por fim, o dosímetro MOSFET mostrou bom desempenho dosimétrico, confirmando seu potencial clínico; fato este que, certamente, contribui para sua maior aceitação na radioterapia. Somado a isto, a obtenção de um modelo computacional adequado proporciona um leque de oportunidades para trabalhos futuros, possibilitando o aprimoramento do instrumento nos mais diversos procedimentos de tratamento do câncer por radiação. / In vivo dosimetry is an essential tool for quality assurance programs in the field of radiotherapy, being a commonly performed procedure with TLDs or diodes. However, a dosimeter coming in popularity growing in recent years is the metal-oxide-semiconductor field-effect transistor (MOSFET) type detector. MOSFET dosimeters fulfill all necessary characteristics to perform the dosimetry in vivo, since they have small size, good precision and viability of measurement, besides its easy handling. Nevertheless, its true differential is to provide dose reading in real time, allowing immediate intervention in the deviations correction of physical parameters and the anticipation of small anatomical changes in the patient during a treatment. Thus, it was proposed the dosimetric characterization of the TN-502RDM-H microMOSFET detector and the construction of its respective computational model in MCNP6. Results showed that MOSFET dosimeter has good reproducibility, good linearity and energy independence for high energy beams of photons and electrons. Regarding linearity, the excellent performance of the MOSFET detector for dose values above 50 cGy stands out, since the dosimeter presented an accuracy of up to 0.3%. In addition, a single calibration factor was obtained with a reproducibility of 2.9% considering photons and high energy electrons. Angular dependencies of 4% and 13% were also observed for irradiations with and without the charged-particle equilibrium (CPE), respectively. It was found a difference of 8% in the response between low energy photon in RQR 3 and RQR 10 qualities. Concerning the computational model, use of the structural characterization techniques of SEM and EDS allowed to estimate geometry and composition of the MOSFET device. Excellent agreement of simulated energy dependence in MCNP6 with that calculated analytically and with literature is highlighted. Finally, MOSFET dosimeter showed good dosimetric performance, confirming its clinical potential. This certainly contributes to their greater acceptance in radiotherapy. Further, obtaining a suitable computational model provides a range of opportunities for future work, making it possible to improve the instrument in a variety of cancer treatment procedures.

abstract: The RADiation sensitive Field Effect Transistor (RADFET) has been conventionally used to measure radiation dose levels. These dose sensors are calibrated in such a way that a shift in threshold voltage, due to a build-up of oxide-trapped charge, can be used to estimate the radiation dose. In order to estimate the radiation dose level using RADFET, a wired readout circuit is necessary. Using the same principle of oxide-trapped charge build-up, but by monitoring the change in capacitance instead of threshold voltage, a wireless dose sensor can be developed. This RADiation sensitive CAPacitor (RADCAP) mounted on a resonant patch antenna can then become a wireless dose sensor. From the resonant frequency, the capacitance can be extracted which can be mapped back to estimate the radiation dose level. The capacitor acts as both radiation dose sensor and resonator element in the passive antenna loop. Since the MOS capacitor is used in passive state, characterizing various parameters that affect the radiation sensitivity is essential. Oxide processing technique, choice of insulator material, and thickness of the insulator, critically affect the dose response of the sensor. A thicker oxide improves the radiation sensitivity but reduces the dynamic range of dose levels for which the sensor can be used. The oxide processing scheme primarily determines the interface trap charge and oxide-trapped charge development; controlling this parameter is critical to building a better dose sensor. / Dissertation/Thesis / M.S. Electrical Engineering 2010

The traditional radiation testing of space electronics has been used for more than fifty years to support the radiation hardness assurance. Its typical goal is to ensure reliable operation of the spacecraft in the harsh environment of space. This PhD research looks into the radiation testing from a different perspective; the goal is to develop radiation testing methods that are focused not only on the reliability of the components but also on a continuous radiation-induced degradation of their performance. Such data are crucial for the understanding of the impact of radiation on the measurement uncertainty of data acquisition systems onboard research space missions.