Intensity Modulated Radiation Therapy (IMRT) is a modern radiotherapy treatment technique used to obtain highly conformal dose distributions. The delivery of IMRT is commonly achieved through the use of a multileaf collimator (MLC). One of the hindrances at present to the widespread use of IMRT is the increased time required for its planning, delivery and verification. In this thesis one particular method of MLC based IMRT, known as Static Multileaf Collimator based IMRT (SMLC-IMRT), has been studied along with methods for improving it???s delivery efficiency. The properties of an MLC commonly used in SMLC-IMRT have been characterised. The potential ramifications of these properties on the dosimetric accuracy of the delivered IMRT field were also investigated. An Interactive Leaf Sequencing (ILS) program was developed that allowed for the manipulation and processing of intensity maps using a variety of methods. The objective of each method was to improve the delivery efficiency whilst maintaining the dosimetric quality of the IMRT treatment. The different methods investigated were collimator angle optimisation, filtration, and intensity level optimisation. The collimator was optimised by identifying the angle at which the minimum monitor unit???s (MU???s) were required when using a sliding-window delivery method. A Savitzky-Golay filter was applied to random intensity maps and suitable filtration parameters identified for filtering clinical IMRT fields, and the intensity levels were optimised based on a deviation threshold. The deviation threshold identified the acceptable level of difference tolerable between the original and modified intensity map. Several IMRT cases were investigated and the impact of each the methods on MU???s, segments and dose distribution observed. As the complexity of IMRT fields increases the dosimetric impact of the MLC properties increases. Complex SMLC-IMRT fields require longer delivery times due to the increased number of MU???s and segments. Collimator optimisation was shown to be a fast and effective means of improving delivery efficiency with negligible dosimetric change to the optimised plan. Modifying intensity maps by applying a filter and optimising the intensity levels did reduce the complexity and improve the delivery efficiency, but also required a dosimetric compromise of the optimised plan.

Intensity Modulated Radiation Therapy (IMRT) is a modern radiotherapy treatment technique used to obtain highly conformal dose distributions. The delivery of IMRT is commonly achieved through the use of a multileaf collimator (MLC). One of the hindrances at present to the widespread use of IMRT is the increased time required for its planning, delivery and verification. In this thesis one particular method of MLC based IMRT, known as Static Multileaf Collimator based IMRT (SMLC-IMRT), has been studied along with methods for improving it???s delivery efficiency. The properties of an MLC commonly used in SMLC-IMRT have been characterised. The potential ramifications of these properties on the dosimetric accuracy of the delivered IMRT field were also investigated. An Interactive Leaf Sequencing (ILS) program was developed that allowed for the manipulation and processing of intensity maps using a variety of methods. The objective of each method was to improve the delivery efficiency whilst maintaining the dosimetric quality of the IMRT treatment. The different methods investigated were collimator angle optimisation, filtration, and intensity level optimisation. The collimator was optimised by identifying the angle at which the minimum monitor unit???s (MU???s) were required when using a sliding-window delivery method. A Savitzky-Golay filter was applied to random intensity maps and suitable filtration parameters identified for filtering clinical IMRT fields, and the intensity levels were optimised based on a deviation threshold. The deviation threshold identified the acceptable level of difference tolerable between the original and modified intensity map. Several IMRT cases were investigated and the impact of each the methods on MU???s, segments and dose distribution observed. As the complexity of IMRT fields increases the dosimetric impact of the MLC properties increases. Complex SMLC-IMRT fields require longer delivery times due to the increased number of MU???s and segments. Collimator optimisation was shown to be a fast and effective means of improving delivery efficiency with negligible dosimetric change to the optimised plan. Modifying intensity maps by applying a filter and optimising the intensity levels did reduce the complexity and improve the delivery efficiency, but also required a dosimetric compromise of the optimised plan.

Three collimators were designed and built with mouse irradiation in mind. They were made to have a shapeable aperture that could deliver strange or complex dose shapes to spots on the animals. Current collimators are either custom-built, expensive, or only provide limited dose shapes. These provide self-customizable collimation at a minimum of cost. A mouse holder was also devised to reproducibly hold a mouse under the collimator. Construction of the holder and of each collimator is also covered. Each collimator was analyzed for flaws, holes, and penumbral width across various shapes of interest. A Norelco MG300 X-ray generator at the Texas A&M Nuclear Science Center was used in these tests. The lead collimator had a radial penumbra of 1.2 mm. The clay / lead shot collimator had a radial penumbra of 1.6 mm. The brass collimator had a radial penumbra of 1.75 mm. Vertical and horizontal penumbras are dependent on distance from the center of the beam. All readings are + 0.3 mm according to the resolution of the scanner used in this experiment. Each collimator is useful for different purposes.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18877号 / 医博第3988号 / 新制||医||1008(附属図書館) / 31828 / 京都大学大学院医学研究科医学専攻 / (主査)教授 武田 俊一, 教授 富樫 かおり, 教授 増永 慎一郎 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

No description available.

O estudo do efeito da colimação nos detectores de radiação sobre a qualidade de imagem do tomógrafo industrial de terceira geração desenvolvido no IPEN/CNEN-SP é descrito neste trabalho. Três conjuntos de colimadores de chumbo foram projetados e confeccionados, sendo um com janelas retangulares de 2 x 5 x 50 mm e outro com 4 x 10 x 50 mm (largura x comprimento x profundidade) e um terceiro com orifício circular de 5 mm de diâmetro x 40 mm de profundidade. Os colimadores foram projetados para poderem ser facilmente substituídos entre si nos detectores de radiação. Paralelamente, foram confeccionados e utilizadas a eletrônica associada, constituída de analisadores de sinais tipo multicanal de 8 bits contendo a unidade de alta tensão e o amplificador. Dentre as vantagens deste sistema destaca-se a sua capacidade de análise multicanal rápida e possuir uma eletrônica mais simples. Valores de resolução energética comparável com a da literatura foram encontrados utilizando a eletrônica desenvolvida acoplada ao detector de radiação de NaI(Tl). Os efeitos dos colimadores foram avaliados pelas medidas tomográficas em um fantom de polimetilmetacrilato contendo componentes multifásicos estáticos (ferro, alumínio e ar). Fontes de radiação com energias de das fontes de 75Se (97 keV, 121 keV, 136 keV, 265 keV, 279 keV e 400 keV), de 137Cs (662 keV) e de 192Ir (317 keV, 468 keV e 602 keV) observou-se que a melhor imagem do fantom foi obtida com os colimadores de janelas retangulares (fendas) de 2 x 5 x 50 mm. Na avaliação dinâmica da formação de bolhas em coluna simuladora de processos industriais, a melhor imagem foi obtida com a fonte de 192Ir. / The study of the effect of collimation in radiation detectors on the image quality of the third-generation industrial CT scanner developed at IPEN / CNEN-SP is described in this work. Three sets of lead collimators were designed and manufactured, one with rectangular windows of 2 x 5 x 50 mm and the other with 4 x 10 x 50 mm (width x length x deep) and a third circular hole of 5 mm diameter x 40 mm deep. The collimators were designed to be easily interchanged in radiation detectors. In parallel, were prepared and used the associated electronics, consisting of multi-channel signal analyzers type of 8 bits containing the high voltage unit and the amplifier. Among the advantages of this system stands out for its ability to fast multichannel analysis and possess a simpler electronics. Values in energy resolution comparable with the literature were found using the developed electronics coupled to the radiation detector of NaI (Tl). The effects of collimators were evaluated by tomographic measurements in a multiphase fantom polymethyl methacrylate containing static components (iron, aluminum and air). Radiation sources with energies of the sources of 75Se (97 keV, 121 keV, 136 keV, 265 keV, 279 keV and 400 keV), 137Cs (662 keV) and 192Ir (317 keV, 468 keV and 602 keV) observed that the best image was obtained fantom collimators with rectangular windows (slits) 2 x 5 x 50 mm. In the dynamic evaluation of formation of bubbles column in a simulated industrial processes the best image at was obtained with the 192Ir source.

O estudo do efeito da colimação nos detectores de radiação sobre a qualidade de imagem do tomógrafo industrial de terceira geração desenvolvido no IPEN/CNEN-SP é descrito neste trabalho. Três conjuntos de colimadores de chumbo foram projetados e confeccionados, sendo um com janelas retangulares de 2 x 5 x 50 mm e outro com 4 x 10 x 50 mm (largura x comprimento x profundidade) e um terceiro com orifício circular de 5 mm de diâmetro x 40 mm de profundidade. Os colimadores foram projetados para poderem ser facilmente substituídos entre si nos detectores de radiação. Paralelamente, foram confeccionados e utilizadas a eletrônica associada, constituída de analisadores de sinais tipo multicanal de 8 bits contendo a unidade de alta tensão e o amplificador. Dentre as vantagens deste sistema destaca-se a sua capacidade de análise multicanal rápida e possuir uma eletrônica mais simples. Valores de resolução energética comparável com a da literatura foram encontrados utilizando a eletrônica desenvolvida acoplada ao detector de radiação de NaI(Tl). Os efeitos dos colimadores foram avaliados pelas medidas tomográficas em um fantom de polimetilmetacrilato contendo componentes multifásicos estáticos (ferro, alumínio e ar). Fontes de radiação com energias de das fontes de 75Se (97 keV, 121 keV, 136 keV, 265 keV, 279 keV e 400 keV), de 137Cs (662 keV) e de 192Ir (317 keV, 468 keV e 602 keV) observou-se que a melhor imagem do fantom foi obtida com os colimadores de janelas retangulares (fendas) de 2 x 5 x 50 mm. Na avaliação dinâmica da formação de bolhas em coluna simuladora de processos industriais, a melhor imagem foi obtida com a fonte de 192Ir. / The study of the effect of collimation in radiation detectors on the image quality of the third-generation industrial CT scanner developed at IPEN / CNEN-SP is described in this work. Three sets of lead collimators were designed and manufactured, one with rectangular windows of 2 x 5 x 50 mm and the other with 4 x 10 x 50 mm (width x length x deep) and a third circular hole of 5 mm diameter x 40 mm deep. The collimators were designed to be easily interchanged in radiation detectors. In parallel, were prepared and used the associated electronics, consisting of multi-channel signal analyzers type of 8 bits containing the high voltage unit and the amplifier. Among the advantages of this system stands out for its ability to fast multichannel analysis and possess a simpler electronics. Values in energy resolution comparable with the literature were found using the developed electronics coupled to the radiation detector of NaI (Tl). The effects of collimators were evaluated by tomographic measurements in a multiphase fantom polymethyl methacrylate containing static components (iron, aluminum and air). Radiation sources with energies of the sources of 75Se (97 keV, 121 keV, 136 keV, 265 keV, 279 keV and 400 keV), 137Cs (662 keV) and 192Ir (317 keV, 468 keV and 602 keV) observed that the best image was obtained fantom collimators with rectangular windows (slits) 2 x 5 x 50 mm. In the dynamic evaluation of formation of bubbles column in a simulated industrial processes the best image at was obtained with the 192Ir source.

A scaled direct energy conversion device was built to convert kinetic energy of singly ionized helium ions into an electric potential by the process of direct conversion. The experiments in this paper aimed to achieve higher potentials and higher efficiencies than ever before. The predicted maximum potential that could be produced by the 150 kV accelerator at the Texas A&M Ion Beam Lab was 150 kV, which was achieved with 92% collection efficiency. Also, an investigation into factors affecting collection efficiency was made. It was concluded that charge was being lost due to charge exchange occurring near the surface of the target which caused positive target atoms to be ejected from the face and accelerated away. Introducing a wire mesh near the face of the target with an electric potential, positive or negative, which aimed to control secondary ion emissions, did not have an effect on the collection efficiency of the system. Also, it was found that the gas pressure inside the chamber did not have an effect on the collection efficiency. The goal of achieving higher electric potentials and higher efficiencies than previous direct conversion work was met.

The field of X-ray imaging and X-ray diffraction have been combined in a new technique called Tomographic Energy Dispersive Diffraction Imaging (TEDDI). This diffraction imaging technique allows 3D sample images to be obtained, non-destructively, where each imaged point contains the atomic structural information associated with its diffraction pattern. The main drawback of the TEDDI technique is the long collection times needed to produce the images. In order to overcome this obstacle the rapid TEDDI (rTEDDI) system has been developed at the University of Manchester's Material Science Centre. The research and development of rTEDDI has been the focus of this PhD thesis. A proof of concept for the rTEDDI imaging technique was obtained using thin samples on station 7.6 SRS Daresbury. In this case a first generation array collimator was used in conjunction with an energy resolving Si pixelated detector. Structural information such as lattice parameters, crystal system and phase identiffcation were obtained for metal, polymer and deer antler bone samples. The use of high Z semiconductor detector material was investigated in order to increase the potential of TEDDI for larger and more dense samples. To enable penetration of larger samples high energy X-rays needed to be utilized. In order to detect these higher energies with a good efficiency the detector media was changed from Si to CdZnTe (CZT).The second generation rTEDDI, using CZT as the detection media, was intended to be used under high flux/high energy synchrotron radiation conditions. Testing of the system under these conditions on station 16.3 SRS Daresbury showed an inability to produce diffraction imaging. An in depth investigation into detector and collimator array performance showed a two fold cause. The ERD2004 detector was unable to handle the high countrates experienced during high flux/high energy synchrotron radiation conditions. The MK1.2 collimator array was found to become partially transparent to X-ray energies around the absorption edge of W resulting in the swamping of the diffraction signal under high flux/high energy synchrotron radiation conditions. A new detector Application Specific Integrated Circuit (ASIC) design, developed by the detector division and the Rutherford Appleton Laboratory, and Data Aquisition (DAQ) system, developed by Aspect Systems, as well as a number of new collimator array designs were developed and tested. Testing of the new collimator array structures have shown positive results and the new HEXITECdetector which was designed to be able to handle high countrates, have shown an unprecedented inter pixel uniformity and energy resolution which have been attributed to the ASIC performance and the use of better quality CZT material.

No description available.