Increased efficacy of light and laser applications in medicine is achieved by accurate light dosimetry. A minimally invasive technique for the determination of the optical coefficients of tissue involves interstitial measurements of the local fluence rate at two or more points in the tissue using isotropic, fibre optic detectors and application of a diffusion model of light propagation. The diffusion models assume simple, homogeneous tissue geometries, possibly oversimplifying the effect of tissue heterogeneities and boundaries. The primary goals of this study were to investigate the influence of realistic finite geometries on the fluence rate distribution and to quantify the systematic errors in the derived optical properties. A Monte Carlo model was developed to predict the fluence rate distribution in any plane of interest in a medium and was verified by comparison with diffusion theory solutions for simple geometries. Fluence rate measurements were made in optically infinite and semi-infinite phantoms for a wide range of optical properties and it was determined that the optical coefficients were derived accurately for phantoms with ueff> 0.2 mm-1 and 2 < ut'<10 mm-1. Measurements were also made in finite spherical volumes with absorbing (Rd = 0.35) and diffuse reflecting (Rd =0.85) boundaries for three optical phantoms and comparisons of the experimental fluence rates with the predictions of the finite volume Monte Carlo model are presented. Boundary effects were observed to be significant within 4 transport mean free paths (mfp') of the boundary. The optical coefficients were derived by applying a diffusion solution for an infinite medium and it was determined that within 2 mfp' of the boundary, the derived ua was overestimated by 40% and underestimated by 20% for the absorbing and reflecting boundaries, respectively. / Thesis / Master of Science (MS)

Computed tomography (CT) is a widely used medical imaging modality. By rotating an x-ray tube and an x-ray detector around the patient, a CT scanner is able to measure the x-ray transmission from all directions and form an image of the patient’s interior. CT scanners in clinical use today all use energy-integrating detectors, which measure the total incident energy for each measurement interval. A photon-counting detector, on the other hand, counts the number of incoming photons and can in addition measure the energy of each photon by comparing it to a number of energy thresholds. Using photon- counting detectors in computed tomography could lead to improved signal-to-noise ratio, higher spatial resolution and improved spectral imaging which allows better visualization of contrast agents and more reliable quantitative measurements. In this Thesis, the feasibility of using a photon-counting silicon-strip detector for CT is investigated. In the first part of the Thesis, the necessary performance requirements on such a detector is investigated in two different areas: the detector element homogeneity and the capability of handling high photon fluence rates. A metric of inhomogeneity is proposed and used in a simulation study to evaluate different inhomogeneity compensation methods. Also, the photon fluence rate incident on the detector in a scanner in clinical use today is investigated for different patient sizes through dose rate measurements together with simulations of transmission through patient im- ages. In the second part, a prototype detector module is used to demonstrate new applications enabled by the energy resolution of the detector. The ability to generate material-specific images of contrast agents with iodine and gadolinium is demonstrated. Furthermore, it is shown theoretically and ex- perimentally that interfaces in the image can be visualized by imaging the so-called nonlinear partial volume effect. The results suggest that the studied silicon-strip detector is a promising candidate for photon-counting CT.

Made available in DSpace on 2014-06-11T19:22:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-08-31Bitstream added on 2014-06-13T18:08:36Z : No. of bitstreams: 1 pontes_w_me_ilha.pdf: 1981877 bytes, checksum: 1035203a106889688fd34bda8f3d2eed (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Neste trabalho descreve-se um sistema detector piroelétrico de intensidade (taxa de fluência de energia) de raios X, para a faixa de ortovoltagem (80 a 300 kVp), constituído essencialmente por uma câmara piroelétrica, um circuito microcontrolado e um display de cristal líquido. A radiação foi produzida por um equipamento de ortovoltagem Siemens Stabilipan II. A câmara possui no seu interior um sensor piroelétrico e um conversor correntetensão de alta sensibilidade, que tem como principal componente um amplificador operacional OPA111 (Burr-Brown). Utilizou-se um osciloscópio digital e um circuito microcontrolado associado ao display para a medição da amplitude dos pulsos de sinal elétrico decorrentes dos pulsos de raios X incidentes no sensor. A resposta do sistema detector piroelétrico foi linear com a intensidade da radiação, em uma faixa de sua resposta, com alguns dos materiais utilizados. O sensor PZT Fe (zirconato titanato de chumbo com ferro) apresentou a melhor sensibilidade para uma grande faixa de tensão sendo assim o mais adequado para utilização em medições de intensidade de radiação X. Dos resultados obtidos, a precisão, resolução e sensibilidade do sistema detector, com os diferentes sensores piroelétricos, associados ao seu baixo custo, construção relativamente simples e facilidade de realização das medições, podem torná-lo muito útil no monitoramento de radiação produzida por equipamentos de ortovoltagem. / In this work a pyroeletric detector system is described for measuring the energy fluence rate (intensity) of x-ray pulses in the ortovoltage range (from 80 to 300 kVp), consisting of a pyroeletric chamber, a microcontrolled circuit, and a liquid crystal display (LCD). The radiation was produced by an ortovoltage equipment Siemens Stabilipan II. The pyroeletric chamber consists essentially of a pyroeletric detector and a current-to-voltage converter that has an operational amplifier OPA 111 (Burr-Brown) as the main component. The electrical pulses produced by the radiation was measured with an oscilloscope and a microcontrolled circuit associated to a LCD. The pyroelectric detector response to a radiation pulse showed linear relationship between the peak electric signal produced by the detector and the intensity of the x-ray pulses in some materials used. The PZT fe showed the most sensibility for a bigger voltage range being thus the most adjusted for measuring the intensity of radiation X. The precision, resolution, and sensibilities of the pyroelectric detector system, with the different pyroeletric sensors, associated with his low cost, relatively simple construction, and easiness for using the device, can turn it very useful for measuring the intensity of radiation produced by ortovoltage equipments.

Orientador: Aparecido Augusto de Carvalho / Banca: Walter Katsumi Sakamoto / Banca: Adelaide de Almeida / Resumo: Neste trabalho descreve-se um sistema detector piroelétrico de intensidade (taxa de fluência de energia) de raios X, para a faixa de ortovoltagem (80 a 300 kVp), constituído essencialmente por uma câmara piroelétrica, um circuito microcontrolado e um display de cristal líquido. A radiação foi produzida por um equipamento de ortovoltagem Siemens Stabilipan II. A câmara possui no seu interior um sensor piroelétrico e um conversor correntetensão de alta sensibilidade, que tem como principal componente um amplificador operacional OPA111 (Burr-Brown). Utilizou-se um osciloscópio digital e um circuito microcontrolado associado ao display para a medição da amplitude dos pulsos de sinal elétrico decorrentes dos pulsos de raios X incidentes no sensor. A resposta do sistema detector piroelétrico foi linear com a intensidade da radiação, em uma faixa de sua resposta, com alguns dos materiais utilizados. O sensor PZT Fe (zirconato titanato de chumbo com ferro) apresentou a melhor sensibilidade para uma grande faixa de tensão sendo assim o mais adequado para utilização em medições de intensidade de radiação X. Dos resultados obtidos, a precisão, resolução e sensibilidade do sistema detector, com os diferentes sensores piroelétricos, associados ao seu baixo custo, construção relativamente simples e facilidade de realização das medições, podem torná-lo muito útil no monitoramento de radiação produzida por equipamentos de ortovoltagem. / Abstract: In this work a pyroeletric detector system is described for measuring the energy fluence rate (intensity) of x-ray pulses in the ortovoltage range (from 80 to 300 kVp), consisting of a pyroeletric chamber, a microcontrolled circuit, and a liquid crystal display (LCD). The radiation was produced by an ortovoltage equipment Siemens Stabilipan II. The pyroeletric chamber consists essentially of a pyroeletric detector and a current-to-voltage converter that has an operational amplifier OPA 111 (Burr-Brown) as the main component. The electrical pulses produced by the radiation was measured with an oscilloscope and a microcontrolled circuit associated to a LCD. The pyroelectric detector response to a radiation pulse showed linear relationship between the peak electric signal produced by the detector and the intensity of the x-ray pulses in some materials used. The PZT fe showed the most sensibility for a bigger voltage range being thus the most adjusted for measuring the intensity of radiation X. The precision, resolution, and sensibilities of the pyroelectric detector system, with the different pyroeletric sensors, associated with his low cost, relatively simple construction, and easiness for using the device, can turn it very useful for measuring the intensity of radiation produced by ortovoltage equipments. / Mestre

The use of lasers for diagnosis and treatment in medical and cosmetic applications is increasing worldwide. Not all of these modalities are superficial and many require laser light to penetrate some distance into the tissue or skin to reach the treatment site. Human skin is highly scattering for light in the visible and near infrared wavelength regions, with a consequent reduction of the fluence rate. Melanin, which occurs in the epidermis of the skin, acts as an absorber in these wavelength regions and further reduces the fluence rate of light that penetrates through the epidermis to a treatment site. In vivo fluence rate measurements are not viable, but validated and calibrated computer models may play a role in predicting the fluence rate reaching the treatment site. A layered planar computer model to predict laser fluence rate at some depth into skin was developed in a commercial raytracing environment (ASAP). The model describes the properties of various skin layers and accounts for both the absorption and scattering taking place in the skin. The model was validated with optical measurements on skin-simulating phantoms in both reflectance and transmission configurations. It was shown that a planar epidermal/dermal interface is adequate for simulation purposes. In the near infrared wavelength region (676 nm), melanin (consisting of eumelanin and pheomelanin) is the major absorber of light in the epidermis. The epidermal absorption coefficient is one of the required input parameters for the computer model. The range of absorption coefficients expected for typical South African skin phototypes (ranging from photo-sensitive light skin, phototype I on the Fitzpatrick scale, to the photo-insensitive darker skin phototype V) was not available. Non-invasive diffuse reflectance spectroscopy measurements were done on 30 volunteers to establish the expected range of absorption coefficients. In the analysis it became apparent that the contributions of the eumelanin and pheomelanin must be accounted for separately, specifically for the Asian volunteers. This is a new concept that was introduced in the diffuse reflectance probe analysis. These absorption coefficient measurements were the first to be done on the expected range of skin phototypes for the South African population. Other authors dealing with diffuse reflectance probe analysis only account for the dominant eumelanin. Both the epidermal absorption coefficient and thickness are important in the prediction of the fluence rate loss. The computer model was used to evaluate the effect of the epidermal absorption coefficient (a parameter dictated by an individual’s skin phototype) and the epidermal thickness on the fluence rate loss through the skin. The epidermal absorption is strongly wavelength dependent with the higher absorption at the shorter wavelengths. In the computer model a longer wavelength of 676 nm (typical for a photodynamic treatment (PDT) of cancer) was used. For the darker skin phototypes (V) only about 30% of the initial laser fluence rate reached a depth of 200 ìm into the skin (just into the dermis). For the PDT application, results from the computer model indicated that treatment times need to be increased by as much as 50% for very dark skin phototypes when compared to that of very light phototypes. / Thesis (PhD)--University of Pretoria, 2012. / Physics / unrestricted

Os processos oxidativos avançados são promissores para a degradação de compostos orgânicos resistentes aos tratamentos convencionais, como o fenol. A fluidodinâmica computacional (CFD) tornou-se uma poderosa ferramenta para analisar processos fotoquímicos por resolver os balanços acoplados de quantidade de movimento, de massa e de radiação. O objetivo deste trabalho é investigar o processo UV/H2O2 num reator fotoquímico anular usando CFD e um modelo cinético mais realista. O modelo em CFD foi criado de forma progressiva. Inicialmente, foram determinados os campos de velocidade para três vazões (30, 60 e 100 L/h). Considerou-se dois diâmetros de lâmpada para reproduzir a configuração experimental do sistema. A discretização foi feita com malhas tetraédricas variando entre 390 000 e 1 200 000 elementos. Quatro modelos de turbulência RANS foram analisados: k-e, k-w, o shear stress transport (SST) e o modelo de tensões de Reynolds (RSM). O campo de velocidades foi validado comparando a DTR com seu levantamento experimental. A próxima etapa foi incluir o mecanismo de degradação de fenol proposto por Edalatmanesh, Dhib e Mehrvar (2008) no modelo em CFD. Trata-se de um modelo cinético baseado em equações dinâmicas para todas as espécies. O campo de radiação foi calculado pelo modelo radial e pela solução da equação de transporte de radiação através do método discrete transfer. As simulações reproduziram dados experimentais abrangendo uma larga gama de concentrações iniciais de fenol, razões molares H2O2/fenol e três potências de emissão das lâmpadas. O campo de velocidades obtido era dependente da vazão: o fluido pode manter movimento helicoidal sobre toda a extensão do reator ou se desenvolver como um escoamento pistonado. O modelo k-e não reproduziu bem o escoamento por não ser adequado para escoamentos rotativos. Os outros modelos geraram curvas de DTR com bom ajuste aos dados experimentais, especialmente o modelo k-w. O desvio médio entre as simulações de degradação de fenol e os dados experimentais é inferior a 8%. Verificou-se que, devido ao escoamento rotativo, os reagentes ficavam concentrados próximos à parede externa e migravam para a região da lâmpada ao longo do reator. A elevada intensidade de radiação na superfície da lâmpada criou uma camada ao seu redor na qual a fotólise do H2O2 ocorreu com grande taxa. Os radicais OH gerados nessa camada eram transportados para a região das paredes por convecção. Isso fez com que a maior parte do fenol fosse atacada na segunda metade do reator e gerou acúmulo do radical próximo à lâmpada na seção de saída do reator, já que o poluente já fora oxidado nessa área. O método discrete transfer previu intensidades de radiação maiores que o modelo radial, e, consequentemente, maior concentração de radicais OH. Os resultados satisfatórios indicam que CFD foi uma ferramenta adequada para analisar este escoamento reativo. / Advanced oxidation processes are a promising technology for degradation of organic compounds resistant to conventional treatments such as phenol. Computational fluid dynamics (CFD) has recently emerged as a powerful tool that allows a deeper understanding of photochemical processes in reactor engineering by solving the coupled momentum, mass and radiation balances. This work aimed to investigate the UV/H2O2 process in an annular photoreactor using CFD and a more realistic kinetic model. A progressive approach was used to develop the CFD reactor model. First, the velocity fields were determined for three volumetric flow rates (30, 60 and 100 L/h). Two lamp diameters were considered to reflect the experimental configuration of the system. Tetrahedral meshes varying form 390,000 to 1,200,000 elements were analyzed to achieve grid independence. For accounting turbulence effects, four RANS models were tested: k-e, k-w, the Shear Stress Transport (SST) and the Reynolds Stress models (RSM). The velocity field was validated through comparison to RTD experimental data. Next step was introducing the mechanism of phenol degradation proposed by Edalatmanesh, Dhib and Mehrvar (2008) into the CFD model. This kinetic model is based on dynamic equations for all species. The fluence rate field was calculated by the radial model and by solving the radiation transport equation with the discrete transfer method. Simulations reproduced experimental data spanning a wide range of initial phenol concentrations, H2O2/phenol molar ratios and three values for lamp power. It was found that the velocity field depends on the volumetric flow rate: either it maintains a swirling motion through the whole reactor or might develop like a plug flow. The k-e model did not represent the RTD data accurately, and the velocity field therefore, since it is not appropriate for swirling flows. The other turbulence models showed good match of RTD, especially the k-w model. Simulations of phenol degradation deviated less than 8% from experimental data. It was possible verified that, due to the swirling inlet effects, reactants got concentrated close to the outer wall and migrated on the lamp direction along the reactor path. High radiation intensities close to the lamp surface created a layer around it where photolysis of H2O2 took place with higher rates. OH radicals were generated in that layer and transported towards the outer wall by convection. This caused most of phenol to be consumed in the second half of the reactor and accumulation of the radical near the lamp and the reactor outlet, since the pollutant in this area was already oxidized. The discrete transfer method predicted higher incident radiation intensity than the radial model, and higher concentrations of OH radicals as a consequence. Satisfactory results indicated that CFD was an appropriate tool for analyzing this reactive flow.

Os processos oxidativos avançados são promissores para a degradação de compostos orgânicos resistentes aos tratamentos convencionais, como o fenol. A fluidodinâmica computacional (CFD) tornou-se uma poderosa ferramenta para analisar processos fotoquímicos por resolver os balanços acoplados de quantidade de movimento, de massa e de radiação. O objetivo deste trabalho é investigar o processo UV/H2O2 num reator fotoquímico anular usando CFD e um modelo cinético mais realista. O modelo em CFD foi criado de forma progressiva. Inicialmente, foram determinados os campos de velocidade para três vazões (30, 60 e 100 L/h). Considerou-se dois diâmetros de lâmpada para reproduzir a configuração experimental do sistema. A discretização foi feita com malhas tetraédricas variando entre 390 000 e 1 200 000 elementos. Quatro modelos de turbulência RANS foram analisados: k-e, k-w, o shear stress transport (SST) e o modelo de tensões de Reynolds (RSM). O campo de velocidades foi validado comparando a DTR com seu levantamento experimental. A próxima etapa foi incluir o mecanismo de degradação de fenol proposto por Edalatmanesh, Dhib e Mehrvar (2008) no modelo em CFD. Trata-se de um modelo cinético baseado em equações dinâmicas para todas as espécies. O campo de radiação foi calculado pelo modelo radial e pela solução da equação de transporte de radiação através do método discrete transfer. As simulações reproduziram dados experimentais abrangendo uma larga gama de concentrações iniciais de fenol, razões molares H2O2/fenol e três potências de emissão das lâmpadas. O campo de velocidades obtido era dependente da vazão: o fluido pode manter movimento helicoidal sobre toda a extensão do reator ou se desenvolver como um escoamento pistonado. O modelo k-e não reproduziu bem o escoamento por não ser adequado para escoamentos rotativos. Os outros modelos geraram curvas de DTR com bom ajuste aos dados experimentais, especialmente o modelo k-w. O desvio médio entre as simulações de degradação de fenol e os dados experimentais é inferior a 8%. Verificou-se que, devido ao escoamento rotativo, os reagentes ficavam concentrados próximos à parede externa e migravam para a região da lâmpada ao longo do reator. A elevada intensidade de radiação na superfície da lâmpada criou uma camada ao seu redor na qual a fotólise do H2O2 ocorreu com grande taxa. Os radicais OH gerados nessa camada eram transportados para a região das paredes por convecção. Isso fez com que a maior parte do fenol fosse atacada na segunda metade do reator e gerou acúmulo do radical próximo à lâmpada na seção de saída do reator, já que o poluente já fora oxidado nessa área. O método discrete transfer previu intensidades de radiação maiores que o modelo radial, e, consequentemente, maior concentração de radicais OH. Os resultados satisfatórios indicam que CFD foi uma ferramenta adequada para analisar este escoamento reativo. / Advanced oxidation processes are a promising technology for degradation of organic compounds resistant to conventional treatments such as phenol. Computational fluid dynamics (CFD) has recently emerged as a powerful tool that allows a deeper understanding of photochemical processes in reactor engineering by solving the coupled momentum, mass and radiation balances. This work aimed to investigate the UV/H2O2 process in an annular photoreactor using CFD and a more realistic kinetic model. A progressive approach was used to develop the CFD reactor model. First, the velocity fields were determined for three volumetric flow rates (30, 60 and 100 L/h). Two lamp diameters were considered to reflect the experimental configuration of the system. Tetrahedral meshes varying form 390,000 to 1,200,000 elements were analyzed to achieve grid independence. For accounting turbulence effects, four RANS models were tested: k-e, k-w, the Shear Stress Transport (SST) and the Reynolds Stress models (RSM). The velocity field was validated through comparison to RTD experimental data. Next step was introducing the mechanism of phenol degradation proposed by Edalatmanesh, Dhib and Mehrvar (2008) into the CFD model. This kinetic model is based on dynamic equations for all species. The fluence rate field was calculated by the radial model and by solving the radiation transport equation with the discrete transfer method. Simulations reproduced experimental data spanning a wide range of initial phenol concentrations, H2O2/phenol molar ratios and three values for lamp power. It was found that the velocity field depends on the volumetric flow rate: either it maintains a swirling motion through the whole reactor or might develop like a plug flow. The k-e model did not represent the RTD data accurately, and the velocity field therefore, since it is not appropriate for swirling flows. The other turbulence models showed good match of RTD, especially the k-w model. Simulations of phenol degradation deviated less than 8% from experimental data. It was possible verified that, due to the swirling inlet effects, reactants got concentrated close to the outer wall and migrated on the lamp direction along the reactor path. High radiation intensities close to the lamp surface created a layer around it where photolysis of H2O2 took place with higher rates. OH radicals were generated in that layer and transported towards the outer wall by convection. This caused most of phenol to be consumed in the second half of the reactor and accumulation of the radical near the lamp and the reactor outlet, since the pollutant in this area was already oxidized. The discrete transfer method predicted higher incident radiation intensity than the radial model, and higher concentrations of OH radicals as a consequence. Satisfactory results indicated that CFD was an appropriate tool for analyzing this reactive flow.

Orientador: Aparecido Augusto de Carvalho / Banca: Cláudio Kitano / Banca: Walter Katsumi Sakamoto / Banca: Tony Inácio da Silva / Banca: Giuliano Pierre Estevam / Resumo: Sensores piroelétricos podem ser utilizados para medir a taxa de fluência de energia (intensidade) da radiação X na faixa de diagnóstico médico e de ortovoltagem. Neste trabalho, foi implementado um sistema eletrônico que pode medir taxa de fluência de energia de radiação gama de 1,25 MeV e fótons X de 6 MV e 15 MV. O sistema é constituído por um sensor piroelétrico, um conversor corrente-tensão de alta sensibilidade e um instrumento para registrar a forma de onda e medir o pulso do sinal produzido pelo sensor. Este instrumento pode ser um osciloscópio, um circuito microcontrolado associado a um display de cristal líquido, ou um módulo de aquisição de dados e um laptop. O sensor piroelétrico e o conversor corrente-tensão foram alojados em uma câmara piroelétrica blindada. Seis tipos de sensores piroelétricos foram avaliados, sendo três cerâmicas e três compósitos. Os resultados obtidos com o sistema eletrônico, utilizando os diferentes tipos de sensores, possibilitaram caracterizá-lo em termos de precisão, resolução e sensibilidade. O sistema apresentou resposta linear com a taxa de fluência de energia da radiação, precisão melhor que 3 % e resolução de 5,56 nW/m2. As constantes piezoelétricas d33 dos sensores utilizados não sofreram alteração após os mesmos terem sido irradiados com 45 Gy de radiação na faixa de radioterapia. Estas características, associadas à importância de se medir a taxa de fluência de energia de radiação ionizante, podem tornar o instrumento piroelétrico muito útil no monitoramento de radiação produzida por equipamentos de radioterapia / Abstract: Pyroelectric sensors have been be used to measure the energy fluence rate (intensity) of x-radiation in the range of medical diagnosis and orthovoltage. In this work, we implemented an electronic system that can measure the energy fluence rate of 1.25 MeV gamma radiation, 6 MV and 15 MV X-photons. The system consists of a pyroelectric sensor, a high sensitivity current-to-voltage converter and an instrument for measuring and recording the waveform of pulses produced by the pyroelectric sensor. This instrument may be an oscilloscope, a microcontrolled circuit associated with a liquid crystal display, or a data acquisition module connected to a laptop. The pyroelectric sensor and the current-tovoltage converter were placed in an shielded pyroelectric camera. Six types of pyroelectric sensors were evaluated, three ceramics and three composites. The results obtained with the electronic system, using different types of sensors, allowed us to characterize it in terms of precision, resolution and sensitivity. The system has linear response to the energy fluence rate of radiation, precision better than 3 % and resolution of 5,6 nW/m2. The piezoelectric constant d33 of the sensors used have not changed after these have been irradiated with 45 Gy of radiotherapy radiation. These characteristics, associated with the importance of measuring the ionizing radiation energy fluence rate may make the pyroelectric instrument very useful in monitoring radiation produced by radiotherapy equipments / Doutor

Made available in DSpace on 2014-06-11T19:32:42Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-25Bitstream added on 2014-06-13T19:22:12Z : No. of bitstreams: 1 pontes_w_dr_ilha.pdf: 799811 bytes, checksum: 398dc35d3e3ae3ef3dfe294f8ba6793c (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Sensores piroelétricos podem ser utilizados para medir a taxa de fluência de energia (intensidade) da radiação X na faixa de diagnóstico médico e de ortovoltagem. Neste trabalho, foi implementado um sistema eletrônico que pode medir taxa de fluência de energia de radiação gama de 1,25 MeV e fótons X de 6 MV e 15 MV. O sistema é constituído por um sensor piroelétrico, um conversor corrente-tensão de alta sensibilidade e um instrumento para registrar a forma de onda e medir o pulso do sinal produzido pelo sensor. Este instrumento pode ser um osciloscópio, um circuito microcontrolado associado a um display de cristal líquido, ou um módulo de aquisição de dados e um laptop. O sensor piroelétrico e o conversor corrente-tensão foram alojados em uma câmara piroelétrica blindada. Seis tipos de sensores piroelétricos foram avaliados, sendo três cerâmicas e três compósitos. Os resultados obtidos com o sistema eletrônico, utilizando os diferentes tipos de sensores, possibilitaram caracterizá-lo em termos de precisão, resolução e sensibilidade. O sistema apresentou resposta linear com a taxa de fluência de energia da radiação, precisão melhor que 3 % e resolução de 5,56 nW/m2. As constantes piezoelétricas d33 dos sensores utilizados não sofreram alteração após os mesmos terem sido irradiados com 45 Gy de radiação na faixa de radioterapia. Estas características, associadas à importância de se medir a taxa de fluência de energia de radiação ionizante, podem tornar o instrumento piroelétrico muito útil no monitoramento de radiação produzida por equipamentos de radioterapia / Pyroelectric sensors have been be used to measure the energy fluence rate (intensity) of x-radiation in the range of medical diagnosis and orthovoltage. In this work, we implemented an electronic system that can measure the energy fluence rate of 1.25 MeV gamma radiation, 6 MV and 15 MV X-photons. The system consists of a pyroelectric sensor, a high sensitivity current-to-voltage converter and an instrument for measuring and recording the waveform of pulses produced by the pyroelectric sensor. This instrument may be an oscilloscope, a microcontrolled circuit associated with a liquid crystal display, or a data acquisition module connected to a laptop. The pyroelectric sensor and the current-tovoltage converter were placed in an shielded pyroelectric camera. Six types of pyroelectric sensors were evaluated, three ceramics and three composites. The results obtained with the electronic system, using different types of sensors, allowed us to characterize it in terms of precision, resolution and sensitivity. The system has linear response to the energy fluence rate of radiation, precision better than 3 % and resolution of 5,6 nW/m2. The piezoelectric constant d33 of the sensors used have not changed after these have been irradiated with 45 Gy of radiotherapy radiation. These characteristics, associated with the importance of measuring the ionizing radiation energy fluence rate may make the pyroelectric instrument very useful in monitoring radiation produced by radiotherapy equipments

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