Tesi: "Linear accelerators in medicine"

1

Klick, George. "High-technology, high energy medical linear accelerators : a review of contemporary problems". Thesis, Queensland University of Technology, 1989. https://eprints.qut.edu.au/35939/1/35939_Klick_1989.pdf.

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The original aim of this project was to study the factors affecting the decision to adopt high energy linear accelerators. including administrative. technical and cltnical aspects. However the potential enormity of the task soon became evident resulting in limitations being placed on the scope of the study. The group of topics finally chosen as the basis for this review-study (listed below) were principally derived from those nominated in the paper by Drew (1987): 1. Optimum Accelerator Energy 2. Aspects of Photon and Electron Dosimetry 3. Dose Delivery Errors 4. Computer Control Systems Reliability 5. Problems with Neutrons at High Energies Each of the above topics is covered in varying degrees of detail which is justified in that the assumed target audience would have some medical physics background but not necessartly at a professional level in radiotherapy. As a result some sections include broader background material. for example NCRP 79 ( 1984) was relied on extensively to introduce the various sections of the neutron aspect of high energy accelerators, following which a review of more recent material is presented.

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2

Delaney, Geoffrey Paul SWSAHS Clinical School UNSW. "The Development of a New Measure of Linear Accelerator Throughput in Radiation Oncology Treatment Delivery - The Basic Treatment Equivalent (B.T.E.)". Awarded by:University of New South Wales. SWSAHS Clinical School, 2001. http://handle.unsw.edu.au/1959.4/33381.

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The measurement of productivity in health care is difficult. Studies in various specialty disciplines of medicine have identified that the variation in complexities (casemix) between departments or hospitals will vary and therefore will affect any basic productivity statistics that are produced. Radiation oncology is a discipline of medicine where no such studies into radiotherapy casemix variations and the effect that these may have on productivity measures have been performed, despite the high capital expenditure involved in the delivery of radiotherapy. Radiation oncology productivity on linear accelerators is currently measured by the number of patients treated or number of treatment fields treated per unit time (usually per hour). These statistics have been collected for many years and productivity assessments were made on the variations in these statistics that exist between departments. However, these statistics do not consider the variations in casemix that occur between departments. These complexity differences may be quite marked and therefore may strongly influence the ability of a department to achieve a high patient or treatment field throughput. This may be seen as 'reduced productivity' with no consideration of the complexity of the caseload seen in the department. In addition, future technological changes that improve patient outcome may be introduced. These changes may make treatment more complex. Using older measures of productivity such as fields per hour or patients per hour will not consider these technological changes and the subsequent changes in complexity and hence departments may be seen as less productive in the future using current methods of analysis unless a more valid measure of productivity that considers complexity variations is introduced. There have only been 3 previous attempts at developing measures of linear accelerator productivity. Each of these models have been developed empirically and have not been clinically validated. No previous attempts have been made in determining a scientifically-derived complexity model that considers the variations in treatment technique. This thesis describes research performed between 1995 and 2001. This research study???s primary aims were to study the factors that affect radiotherapy treatment time and treatment complexity and to develop a model of linear accelerator productivity that does consider complexity variations in radiotherapy treatment delivery. This model is called the Basic Treatment Equivalent (B.T.E.). This series of trials examines the old models of linear accelerator productivity, describes the derivation and validation of the BTE model both in Australasia and the United Kingdom, identifies the factors that contribute to treatment time and treatment complexity, describes the development of a pilot model of productivity of gynaecological brachytherapy and outpatient chemotherapy using similar BTE methodology, discusses the potential uses of the BTE model, recent independent reviews of BTE by other groups, and the advantages and disadvantages of using such a model. This research has shown that it is possible to identify the various factors that contribute to treatment time and treatment complexity and to derive a model of linear accelerator productivity that considers the variations in complexity. The BTE model has been clinically validated in Australia, New Zealand and a couple of departments in the United Kingdom and Canada and has been adopted as a new measure by various groups. It requires regular updating to maintain currency particularly as there are frequent improvements in radiation treatment technology. Future studies should identify the differences these technological enhancements make to productivity. The BTE derived from outpatient chemotherapy delivery and gynaecological brachytherapy delivery shows promise although these models require further research with the assistance of other departments.

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3

Satory, Philip Reynard. "An Investigation into EPID Flood Fields Independent from the Linear Accelerator Beam". Thesis, University of Canterbury. Physics and Astronomy, 2008. http://hdl.handle.net/10092/2185.

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The EPID (electronic portal imaging device) was designed for in vivo imaging of patients during radiotherapy treatment. The ability of EPIDs to promptly acquire two dimensional data, lends them to be considered for use in quality assurance of the linac. This thesis set out to investigate the possibility of using a radionuclide, technetium 99 m (Tc99m), to produce a flood field for the calibration of an EPID, because using a beam calibrated EPID to measure the beam is self-referential. The difference in relative response between the energy spectrum of a 6MV beam and the Tc99m was investigated using EGSNRC DoseXYZ Monte Carlo Modelling. The relative output ratio was calculated to be less than 1.6%. The dose response of the EPID with respect to dose rate was checked using different activities of Tc99m and found to be linear. The flatness from a phantom was calculated, with a model in MATLAB, for a range of heights, overlaps, thickness, and deformations, to find the optimum balances between signal strength and flatness. This model was checked for accuracy using diagnostic radiographic film. The culmination of the energy response, linearity and the calculated flatness is a flood field taken with a flood phantom on the EPID with low signal strength. To get a signal to noise ratio of 3% the mean of over 2000 flood field images were used. This accuracy was not adequate for clinical use but the averaging of pixels it is accurate enough for QA.

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4

Cashmore, Jason. "Operation, characterisation & physical modelling of unflattened medical linear accelerator beams and their application to radiotherapy treatment planning". Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4616/.

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The flattening filter is a conical shaped piece of metal sitting within the treatment head of a linear accelerator, used to produce a flat, uniform beam of X-rays from the forward-peaked distribution exiting the target. Despite their routine use since the introduction of the linac in the 1950’s, however, there are still several unresolved issues surrounding their use. The photon scatter and electron contamination introduced by modifying the fluence are difficult to model, as is the variation in energy spectrum caused by differential absorption across the field. Leakage radiation also causes increased whole body doses to the patient, and the filter itself causes acts as an amplifier for beam bending and steering issues. With advances in tumour imaging, dose optimisation and in-room image-guidance it is now possible to locate a tumour accurately in space and to design radiation fields to conform to its shape, avoiding adjacent normal and critical tissues. This active production of non-flat fields means that the prerequisite for flat fields no longer exists, and the filter is potentially no longer a necessary component. This thesis reports on research to produce a filter-free linear accelerator, from basic operation and optimisation, dosimetric characterisation and beam modelling, through to treatment planning and dose delivery. FFF beams have been shown reduce many of the problems seen with the current generation of linear accelerators, producing beams that are inherently more stable, simple to model and with reduced patient leakage (leading to reduced secondary cancers). The increase in dose rate also translates into shorter treatment times for many treatments, aiding patient comfort and reducing problems associated with intra-fraction motion.

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5

Horne, Christopher Douglas. "Design and analysis of linear induction accelerators". Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309929.

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6

Crossman, John S. P. "Microdosimetry of photoneutrons around medical linear accelerators". Thesis, University of St Andrews, 1997. http://hdl.handle.net/10023/13366.

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Photoneutrons produced in the vicinity of medical linear accelerators for therapy, constitute a hazard which is difficult to assess and monitor. The aims of the project were to develop new techniques, using microdosimetry, which would be suitable for the improved quality control of pulsed photon beams and for the assessment of the associated photoneutron hazard in typical treatment facilities from the perspective of the patients and staff. The measurements of photoneutron yields and equivalent doses were obtained using activation analysis detectors around a 10 MV LINAC. To obtain adequate statistical precision, an optimum thickness of 2.5 cm of polyethylene was used that doubled the detector's sensitivity. This enabled the yields and spatial distribution of the low intensity field to be recorded. Photoneutron equivalent dose-rates of up to 0.104 Sv.h-1, or 0.1% of the useful photon dose- rates, were measured. In the literature, however, it was found that equivalent dose-rates could reach as high as 1 % of the useful photon treatment dose-rate for machines operating at X ray energies of ≥18 MV. Thus it is recommended that to uphold the principle of ALARA, such high energies (≥18 MV) should only be used when no lower energy machine is available. Microdosimetry with a tissue equivalent proportional counter (TEPC) microdosimeter, enabled the photoneutron contribution to the quality spectrum to be identified in the maze to the treatment room of the 10 MV LIN AC, and the photoneutrons there were assigned a radiation weighting factor of 20. The known problems concerning the rf interference and very high pulsed dose-rates inside the treatment room proved too severe to obtain meaningful results with the TEPC. The microdosimeter did however provide useful diagnostic information. Furthermore, a novel calibration technique for TEPC's was developed and an established one, the proton-edge method, was improved. A new approach was adopted to conduct microdosimetry in the vicinity of medical accelerators. This involved the design of a condensed phase microdosimeter comprising, a miniature CsI(T1) scintillator coupled to an optical fibre 20 m long, for conducting in-beam, on-line measurements of quality spectra. However, Cerenkov light and scintillation light produced in the optical fibre by the radiation fields was the cause of strong interference that has yet to be overcome. The application of the microdosimeter, which is still under development, to brachytherapy is proposed for in-vivo measurements.

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7

Plostinar, Ciprian. "Design principles for high power linear accelerators". Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:c425c3c8-772c-49a0-8764-257ae6af5bd6.

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The demand for high power proton beams is at an all time high. The global community has identified many applications ranging from spallation sources, material irradiation facilities and secondary beams factories to accelerator driven systems for energy production, transmutation of waste or production of tritium. The typical path to high power beams involves the use of a linac at least in the lower energy stages. For high intensity, high power operation, significant developments are needed particularly in the linac section and the front end of the machine. Consequently, this thesis brings original contributions in tackling several limiting aspects to do with two major pillars of high power operation in linacs: energy and intensity. One of the major decisions in any linac design concerns the choice of normal accelerating structures. The general aim of every designer is to find the optimal path to the final energy without compromising the beam quality or increasing excessively the structure complexity. In the absence of a much needed comparative assessment of accelerating cavities, this choice was often made based on available local expertise rather than solid reasoning. This problem is tackled at length in two chapters of this thesis in which a framework is created for a methodical examination of available structures. The result is the first systematic analysis of normal conducting structures for proton acceleration which includes beam dynamics, electromagnetic, mechanical, thermal and vacuum aspects of cavity design. On the intensity side, several innovative developments have arisen through involvement in the Front End Test Stand Project (FETS) and the ISIS linac upgrade efforts. Beam dynamics studies for the Medium Energy Beam Transport line (MEBT) of FETS, as well as an analysis of several other MEBT designs for existing international projects, highlighted the difficulty in reducing beam loss and emittance growth in high current MEBT lines incorporating beam choppers. Through end-to-end tracking studies, it was shown that the initial beam quality produced in the MEBT will heavily influence the emittance evolution, halo development and beam loss in subsequent structures. As a result, a novel distributed MEBT design is proposed as an alternative, allowing better matching and chopping as well as higher intensity, lossless operation. Further downstream, the beam quality is not only affected by initial mismatch and MEBT beam quality, but by the choice of operating points as well. Theoretical work developed over the last two decades indicate that safe tunes outside conventional equipartitioning limits can be found, but the lack of experimental verification remains a problem. This problem was tackled through an experimental campaign at J-PARC, where for the first time emittance exchange driven by the kz/kt = 2 resonance was measured in a linac with emittance ratios close to 1. Finally, these principles are applied to the design of a future upgrade of the ISIS linac. Three linac options have been developed accelerating the beam to 100, 180 and 800 MeV opening the possibility of MW-level operation in ISIS.

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8

Wang, Yi Zhen 1965. "Photoneutrons and induced activity from medical linear accelerators". Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81453.

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This study involves the measurement of the neutron equivalent dose ( NED) and the induced activity produced from medical linear accelerators. For the NED, various parameters such as the profile, field effects and energy responses were studied. The NED in a Solid Water(TM) phantom was measured and a new quantity, the neutron equivalent dose tissue-air ratio (NTAR), was defined and determined. Neutron production for electron beams was also measured. For the induced activity, comparisons were carried out between different linacs, fields and dose rates. The half life and activation saturation were also studied. A mathematical model of induced activity was developed to explain the experimental results. Room surveys of NED and induced activity were performed in and around a high energy linear accelerator room. Unwanted doses from photoneutrons and induced activity to the high energy linear accelerator radiotherapy staff and patient were estimated.

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9

Taheri, Faissal Bakkali. "Numerical and experimental studies of coherent Smith-Purcell radiation". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:d483c501-ba46-4e08-9d38-5af29211aedc.

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This thesis investigates the properties of coherent Smith-Purcell radiation (cSPr) at femtosecond-scale in the case of electrons bunches in the ultrarelativistic regimes. Of particular interest is the use of cSPR as a diagnostic tool to determine the longitudinal time profiles of such bunches, the study of azimuthal distribution of the radiated energy, and a contribution to the understanding of polarization properties. The study consists in a first theoretical part carried mostly in the context of the surface-current theory, supported with insights from particle-in-cell simulations. Then, as a step toward a better determination of time profile, the question of phase reconstruction is addressed through the design of a new algorithm proposed in this thesis and tested in known challenging cases. Experimental results are then presented, spanning shifts having taken place at the FACET facility at SLAC, Stanford, between 2013 and 2015.

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10

Rodríguez, Castillo Miguel Lázaro. "Automation of the Monte Carlo simulation of medical linear accelerators". Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/392626.

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The main result of this thesis is a software system, called PRIMO, which simulates clinical linear accelerators and the subsequent dose distributions using the Monte Carlo method. PRIMO has the following features: (i) it is self- contained, that is, it does not require additional software libraries or coding; (ii) it includes a geometry library with most Varian and Elekta linacs; (iii) it is based on the general-purpose Monte Carlo code PENELOPE; (iv) it provides a suite of variance-reduction techniques and distributed parallel computing to enhance the simulation efficiency; (v) it is graphical user interfaced; and (vi) it is freely distributed through the website http://www.primoproject.net In order to endow PRIMO with these features the following tasks were conducted: - PRIMO was conceived with a layered structure. The topmost layer, named the GLASS, was developed in this thesis. The GLASS implements the GUI, drives all the functions of the system and performs the analysis of results. Lower layers generate geometry files, provide input data and execute the Monte Carlo simulation. - The geometry of Elekta linacs from series SU and MLCi were coded in the PRIMO system. - A geometrical model of the Varian True Beam linear accelerator was developed and validated. This model was created to surmount the limitations of the Varian distributed phase-space files and the absence of released information about the actual geometry of that machine. This geometry model was incorporated into PRIMO. - Two new variance-reduction techniques, named splitting roulette and selective splitting, were developed and validated. In a test made with an Elekta linac it was found that when both techniques are used in conjunction the simulation efficiency improves by a factor of up to 45. - A method to automatically distribute the simulation among the available CPU cores of a computer was implemented. The following investigations were done using PRIMO as a research tool : - The configu ration of the condensed history transport algorithm for charged particles in PENELOPE was optimized for linac simulation. Dose distributions in the patient were found to be particularly sensitive to the values of the transport parameters in the linac target. Use of inadequate values of these parameters may lead to an incorrect determination of the initial beam configuration or to biased dose distributions. - PRIMO was used to simulate phase-space files distributed by Varian for the True Beam linac. The results were compared with experimental data provided by five European radiotherapycenters. It was concluded thatthe latent variance and the accuracy of the phase-space files were adequate for the routine clinical practice. However, for research purposes where low statistical uncertainties are required the phase-space files are not large enough. To the best of our knowledge PRIMO is the only fully Monte Carlo-based linac and dose simulation system , addressed to research and dose verification, that does not require coding tasks from end users and is publicly available.
El principal resultado de esta tesis es un sistema informático llamado PRIMO el cual simula aceleradores lineales médicos y las subsecuentes distribuciones de dosis empleando el método de Monte Carlo. PRIMO tiene las siguiente características: (i) es auto contenido, o sea no requiere de librerías de código ni de programación adicional ; (ii) incluye las geometrías de los principales modelos de aceleradores Varían y Elekta; (iii) está basado en el código Monte Carlo de propósitos generales PENELOPE; (iv) contiene un conjunto de técnicas de reducción de varianza y computación paralela distribuida para mejorar la eficiencia de simulación; (v) tiene una interfaz gráfica de usuario; y (vi) se distribuye gratis en el sitio web http://vvww.primoproject.net. Para dotar a PRIMO de esas características, se realizaron las tareas siguientes: - PRIMO se concibió con una estructura de capas. La capa superior, nombrada GLASS, fue desarrollada en esta tesis. GLASS implementa la interfazgráfica de usuario, controla todas las funciones del sistema y realiza el análisis de resultados. Las capas inferiores generan los archivos de geometría y otros datos de entrada y ejecutan la simulación Monte Carlo. - Se codificó en el sistema PRIMO la geometría de los aceleradores Elekta de las series SLi y MLC. - Se desarrolló y validó un modelo geométrico del acelerador TrueBeam de Varian. Este modelo fue creado para superar las limitaciones de los archivos de espacio de fase distribuidos por Varian, así como la ausencia de información sobre la geometría real de esta máquina. Este modelo geométrico fue incorporado en PRIMO. - Fueron desarrolladas y validadas dos nuevas técnicas de reducción de varianza nombradas splitting roulette y selective splitting. En pruebas hechas en un acelerador Elekta se encontró que cuando ambas técnicas se usan en combinación, la eficiencia de simulación mejora 45 veces. - Se implementó un método para distribuir la simulación entre los procesadores disponibles en un ordenador. Las siguientes investigaciones fueron realizadas usando PRIMO como herramienta: - Fue optimizada la configuración del algoritmo de PENELOPE para el transporte de partículas cargadas con historia condensada en la simulación del linac. Se encontró que las distribuciones de dosis en el paciente son particularmente sensibles a los valores de los parámetros de transporte usados para el target del linac. El uso de va lores inadecuados para esos parámetros puede conducir a una incorrecta determinación de la configuración del haz inicial o producir sesgos en las distribuciones de dosis. - Se utilizó PRIMO para simular archivos de espacios de fase distribuidos por Varian para el linac TrueBeam. Los resultados se compararon con datos experimentales aportados por cinco centros de radioterapia europeos. Se concluyó que la varianza latente y la exactitud de estos espacios de fase son adecuadas para la práctica clínica de rutina. Sin embargo estos espacios de fase no son suficientemente grandes para emplearse en investigaciones que requieren alcanzar una baja incertidumbre estadística. Hasta donde conocemos, PRIMO es el único sistema Monte Carlo que simula completamente el acelerador lineal y calcula la dosis absorbida, dirigido a la investigación y la verificación de dosis que no requiere del usuario tareas de codificación y está disponible públicamente

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11

GUIMARÃES, NILMARA ALMEIDA. "METROLOGICAL EVALUATION OF THE RADIATION FIELD SIZE BY LINEAR ACCELERATORS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2011. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=34951@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
O objetivo desta dissertação é o estudo de procedimentos para avaliação da confiabilidade metrológica do tamanho de campo irradiado (TCI) por aceleradores lineares. No contexto das recentes alterações no panorama regulamentar dos serviços de radioterapia, com a implementação da RDC número 20, em 2006, pela Agência Nacional de Vigilância Sanitária (ANVISA), foi estabelecida a compulsoriedade do uso do densitômetro óptico na verificação do TCI, como parte do controle da qualidade. Questões associadas à implementação prática dos recentes requisitos para medição do tamanho de campo irradiado e as recentes indicações do potencial uso de filmes radiocrômicos para o controle da qualidade em radioterapia motivaram a realização do presente trabalho. Foram empregados três diferentes procedimentos para avaliação do tamanho de campo irradiado por aceleradores lineares utilizados em treze serviços de radioterapia localizados no Estado do Rio de Janeiro, utilizando filmes radiocrômicos EBT QD mais, RTQA, densitômetro óptico DensiX tipo T52001 ou scanner de transmissão Microtek. Os resultados destacam a contribuição das fontes de incerteza de medição para cada procedimento realizado e indicam a necessidade de considerá-la na avaliação da conformidade utilizando o densitômetro óptico (DO). Devido às propriedades do filme radiocrômico RTQA, o mesmo não pode ser utilizado no procedimento de medição com DO. Em conclusão, o uso do procedimento de medição utilizando scanner mostrou-se mais adequado para avaliação das dimensões de campos de radiação não-homogêneos.
The objective of the present work is to study different procedures for metrological evaluation of the size of the radiation field emitted by linear accelerators. In the context of the recent requirements determined by the publication of the RDC number 20, in 2006, by National Agency for Sanitary Vigilance (Anvisa), the compulsory use of the optical densitometer for the measurements of the field size during quality control tests was introduced. Practical implementation issues associated with these requirements and the recent studies indicating the potential use of radiochromic films for measurements of the field size motivated the present work. Three different procedures were employed in order to evaluate the radiation field size emitted by linear accelerators used in thirteen radiotherapy services located in Rio de Janeiro, using radiochromic films EBT QD plus and RTQA, optical densitometer DensiX type T52001 or scanner Microtek. The results indicate the contribution of the measurement uncertainty associated to each procedure performed, highlighting the importance of its consideration during tests for conformity assessment with the recently required optical densitometer. Nevertheless, the RTQA radiochromic film properties precluded its use in the procedure using optical densitometer. In conclusion, among the evaluated procedures for radiation field evaluation, the use of the scanner was the most appropriate, especially if dimensional non-homogeneities are present.

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Garland, James Matthew. "Beam dynamics studies of the EMMA linear non-scaling FFAG". Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/beam-dynamics-studies-of-the-emma-linear-nonscaling-ffag(5b375a2d-0636-422d-a0d6-2cc941ebd01f).html.

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The development of charged particle accelerators is today reaching far beyond the realm of fundamental particle physics research. Many non-trivial social and political problems may find part of their solution lies in accelerator physics. For example, with fossil fuels becoming ever more controversial and expensive to obtain, the use of Accelerator Driven Sub-critical Reactors (ADSR) powered by rapid cycling, high current proton accelerators and thorium fuel could become part of the energy solution. Through the simplicity of the Bragg peak, cancer therapy could be enhanced through the use of high repetition rate, variable energy proton accelerators small enough to use in treatment centres. The growing problem of long lived nuclear waste storage could become a moot point through the use of high current, high power proton accelerators coupled with neutron spallation. These rapidly growing areas of study are fuelled by the development of the Fixed-Field Alternating-Gradient (FFAG) accelerator, and more recently the non-scaling FFAG. The FFAG has the ability to accelerate high current, low quality bunches of particles in very short time scales due to the fixed-field nature of its magnets. This rapid acceleration can be of the order 500 nanoseconds to 1 microsecond meaning a fast cycling rate of the machine is possible. This allows the realistic development of the ADSR, proton therapy machine and even the muon accelerator. The Electron Model with Many Applications (EMMA) accelerator is the world's first linear non-scaling FFAG and is an electron proof-of-principle accelerator based at Daresbury Laboratory, UK. EMMA can accelerate over its energy range of 10 - 20 MeV in approximately 5 - 10 machine revolutions (~275 - 500 nanoseconds) using fixed-frequency novel acceleration techniques. The accelerator contains fixed-field, constant gradient quadrupole magnets which provide all the bending and focussing to the particles. Due to the linear non-scaling nature of EMMA, many transverse integer tune values are crossed which typically cause resonant effects resulting in bunch degradation and loss. It was proposed and demonstrated that rapid crossing (in 5 - 10 turns) of integer tune values in EMMA did not result in transverse amplitude growth and particle loss. If the wider societal goals of the non-scaling FFAG are to be realised, protons and other heavy ions must be accelerated. Current technological limitations dictate that longer acceleration times of the order 1000's of turns would be necessary in proton machines of similar design to EMMA. Hence slower integer tune crossing was studied using acceleration in a synchrotron bucket in EMMA. It was found experimentally that below the nominal EMMA operating acceleration rate of 2.0 MV per turn, instabilities begin to manifest. This was indicated in the growth of closed orbit distortion (COD) and through simulation it was found that betatron amplitude growth coupled with COD resulted in eventual loss of particles to the physical aperture when crossing integer tunes. Through simulation, the amplitude growth of particles crossing integer tunes in the EMMA non-scaling FFAG was found to agree with a theory of resonance crossing proposed by R. Baartman. This theory shows that amplitude growth is proportional to $1/\sqrt(Q')$ where $Q'$ is the tune crossing rate of the particles. This means that the slower the acceleration, the slower an integer tune is crossed and hence more amplitude is gained. It was also shown that strength of the magnetic errors driving the resonant conditions was proportional to the amplitude growth.

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Malysheva, Larisa Ivanovna. "Numerical investigation of spin dynamics problems in linear and circular accelerators". Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539513.

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14

Thien, Joseph R. "High order parametric x-radiation from silicon and lithium fluoride crystal monochromators". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA305981.

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15

Sheikh-Bagheri, Daryoush. "Monte Carlo study of photon beams from medical linear accelerators, optimization, benchmark and spectra". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ37077.pdf.

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16

PASSARO, BRUNO M. "Análise quantitativa dos resultado dos testes de controle de qualidade em radioterapia". reponame:Repositório Institucional do IPEN, 2011. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10038.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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17

Assatel, Omran. "Characterisation of photon and neutron spectra in medical linear accelerators using theoretical and experimental techniques". Thesis, University of Surrey, 1996. http://epubs.surrey.ac.uk/804743/.

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18

Davis, Michael Roger. "The development of intra-train beam stabilisation system prototypes for a future linear collider". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:1373c535-b1e3-43d2-8dbf-98a2b6fba6e2.

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Any future linear collider requires a beam stabilisation system at the interaction point to the to maintain luminosities. This thesis details the development of prototypes of three such systems based at the Accelerator Test Facility 2 (ATF2) at KEK, Japan. The upstream feedback system utilises two stripline beam position monitors (BPMs) and two stripline kickers located in the ATF2 extraction line to stabilise the position and angle of the beam; the correction is then measured downstream at the ATF2 beam waist by a cavity BPM. The feedforward system uses the two upstream stripline BPMs to measure the position of the beam and calculate a correction signal which is then implemented locally by a stripline kicker located near the beam waist; the correction is then measured at the beam waist by a cavity BPM. The IP feedback system uses the position measured at the ATF2 beam waist by a cavity BPM and implements a correction based on this position using the local stripline kicker; the correction is then measured at the beam waist by a cavity BPM. Tests of the upstream feedback system have demonstrated stabilisation of the ATF2 beam waist at approximately the 300 nm level; tests of the feedforward and IP feedback systems have demonstrated stabilisation of the ATF2 beam waist at approximately the 100 nm level. Additional work undertaken to improve the processing electronics of the stripline BPMs is detailed. The cavity BPMs and their electronics are characterised and offline analysis techniques to improve the BPM resolutions set out. Results demonstrating resolutions of approximately 350 nm for the stripline BPMs and 80 nm for the cavity BPMs are presented.

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19

Bakken, Jonas Sjolte. "Study and development of Solid State based Long Pulse Klystron Modulators for future Linear Accelerators at CERN". Thesis, Norwegian University of Science and Technology, Department of Electrical Power Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9640.

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A new Klystron modulator is to be developed as a part of the new Linear Accelerator (LINAC4) project that is currently running at CERN. The Klystron modulator is required to supply a pulsed output voltage of -100 kV / 20 A with a repetition rate of 2 Hz and a pulse length of 800 us. In addition to this, the Klystron modulator must also handle arcing in the Klystron, and allow for no more than 10 J of energy to be dissipated in the arc in such a case. This thesis studies possible solid state based topologies that could be relevant for the Klystron modulator. A single switch topology, based on a 12 kV IGCT switch and a pulse transformer, is studied in detail and developed as a full scale prototype. Preliminary test results indicate that this will provide a satisfactory solution that meets the requirements. A second topology based on the Parallel Resonant Converter (PRC) was studied in detail through analysis and simulations. This showed to be a promising solution that could be an improvement compared to the single switch topology. The PRC is fully controllable and thus offers a flexible solution that can meet various demands. The topology also showed very good arc handling capabilities, and the PRC can be configured to protect the Klystron by its natural response.

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20

Soubra, Mazen Ahmed. "Linac head scatter factor for asymmetric radiation field". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ26868.pdf.

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21

Al-Shantaf, Abdulraouf O. "A Computer-Based Process Control System for a Target Station in a LINAC Facility". Thesis, University of North Texas, 1999. https://digital.library.unt.edu/ark:/67531/metadc278077/.

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An event-driven, sequential, process control system was designed for International Isotopes, Inc., to automate and remotely control a target station at the company's linear accelerator facility. The designed system consisted of two major sections: a software program (virtual instrument), which was developed by LabVIEW, and a hardware interface (FieldPoint Modular Distributed I/O System by National Instrument), which had to be a pre-developed system that did not require customization. The designed virtual instrument was tested on a simulation model that mimed the target station. The result was a valid design.

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22

Mears, Michael Laine. "Geometry estimation and adaptive actuation for centering preprocessing and precision measurement". Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-03312006-125319/.

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Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2006.
Dr. Richard F. Salant, Committee Member ; Dr. Shreyes N. Melkote, Committee Member ; Dr. Francis M. Kolarits, Committee Member ; Dr. Jane C. Ammons, Committee Member ; Dr. Thomas R. Kurfess, Committee Chair.

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23

NONATO, FERNANDA B. C. "Projeto, construção e caracterização de sistemas de referência para feixes de elétrons de aceleradores clínicos". reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23232.

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Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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24

Weathersby, Stephen. "Damping higher order modes in the PEP-II B-factory storage ring collider". Diss., Connect to online resource - MSU authorized users, 2007.

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Thesis (Ph.D.)--Michigan State University. Dept. of Physics and Astronomy, 2007.
Title from PDF t.p. (viewed on August 18, 2009) Includes bibliographic references (p. 175-179). Also issued in print.

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25

BERDAKY, MAFALDA F. "Implantacao de um servico de radioterapia com acelerador linear (fotons): testes de aceitacao, dosimetria e controle de qualidade". reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10873.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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26

Metral, Elias. "Coupled Landau damping of transverse coherent instabilities in particle accelerators". Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10048.

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L'effet du couplage lineaire entre les plans transversaux d'un accelerateur circulaire sur l'amortissement de landau des instabilites coherentes est etudie en considerant deux distributions caracteristiques de frequences (lorentzienne et elliptique). Celles-ci correspondent a des cas limites modelisant des spectres avec et sans longues queues. Un critere general de stabilite, ou interviennent la force du couplage (du aux quadrupoles tournes) et la distance des nombres d'ondes betatroniques aux resonances de couplage, est obtenu dans les deux cas. Ce dernier revele la possibilite de partager les dispersions de frequences stabilisatrices entre les deux plans, ce qui peut considerablement ameliorer la stabilite coherente du faisceau, en particulier dans les cas ou la situation est plus critique dans un plan. Une seconde observation importante est que l'effet d'une grande partie imaginaire de l'impedance de couplage, qui normalement requiert une dispersion de frequences equivalente pour l'amortissement de landau, peut etre compense (du moins dans un plan) par un choix judicieux du couplage. Les resultats d'experiences effectuees au synchrotron a protons (ps) du cern confirment le comportement general predit par la theorie. Le mecanisme de l'amortissement de landau couple pourrait donc expliquer pourquoi une machine comme le ps peut etre stabilisee en rapprochant le point de fonctionnement pres d'une resonance de couplage. Il peut par consequent etre utilise pour determiner des valeurs optimales du point de fonctionnement et de la force du couplage lineaire.

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27

Blaskovic, Kraljevic Neven. "Development of a high-precision low-latency position feedback system for single-pass beamlines using stripline and cavity beam position monitors". Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:0286d951-d177-4d3a-8bce-a50e6ccb8645.

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The FONT beam-based, intra-train feedback system has been designed to provide beam stability at single-pass accelerators, such as at the interaction point (IP) of the International Linear Collider. Two FONT feedback systems have been commissioned at the Accelerator Test Facility (ATF) at KEK, Japan, and the operation, optimisation and performance of these systems is the subject of this thesis. For each system, the accelerator is operated with two-bunch trains with a bunch separation of around 200 ns, allowing the first bunch to be measured and the second bunch to be subsequently corrected. The first system consists of a coupled-loop system in which two stripline beam position monitors (BPMs) are used to characterise the incoming beam position and angle, and two kickers are used to stabilise the beam. A BPM resolution of about 300 nm has been measured. On operating the feedback system, a factor ~ 3 reduction in position jitter has been demonstrated at the feedback BPMs and the successful propagation of this correction to a witness BPM located 30 m downstream has been confirmed. The second system makes use of a beam position measurement at the ATF IP that is used to drive a kicker to provide a local correction. The measurement is performed using a high-resolution cavity BPM with a fast decay time of around 20 ns designed to allow multiple bunches to be resolved. The linearity of the cavity BPM system and the noise floor of the electronics are discussed in detail. The performance of the BPM system under standard ATF operation and with the beam waist at the BPM is described. A BPM resolution of about 50 nm has been measured. This IP feedback system has been used to stabilise the beam position to the 75 nm level.

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28

Bromwich, Talitha. "Development of high-resolution cavity beam position monitors for use in low-latency feedback systems". Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:7d3fada0-2676-4983-8e2c-16d2d6d4f7d0.

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The FONT beam-based, intra-train feedback system has been designed to provide beam position stabilisation in single-pass accelerators. A FONT feedback system utilising position information from three high-resolution cavity beam position monitors (BPMs) has been commissioned at the interaction point (IP) of the Accelerator Test Facility 2 (ATF2) at KEK, Japan. The ultimate goal of the feedback in the IP region is to stabilise the low-emittance electron beam to the nanometre level. The operation, optimisation and resolution performance of this IP system forms the subject of this thesis. The IP feedback system makes use of beam position measurements from the BPMs to drive an upstream kicker and provide a local correction. The BPMs have a fast decay time of ~25 ns to allow bunches within the beam train to be resolved. The operation of the IP BPMs, the noise floor, and position sensitivity to phase are discussed in detail. Attempts are made to diagnose an unwanted ~60 MHz oscillation in the cavity signals, which is bunch charge-dependent and thus likely beam generated. The BPM resolution estimate was notably improved from 50 nm to 20 nm using waveform integration in analysis of the BPM signals. A multi-parameter fit was used to address inaccurate calibrations and charge-dependencies to achieve more consistent resolution performance and produce a best-ever resolution estimate for the BPMs of 17.5 ± 0.4 nm. A novel mode of IP beam position stabilisation using two BPMs as input to the feedback has been successfully demonstrated. The beam position was stabilised to 57 ± 4 nm, as measured at an independent BPM. Feedback performance was improved to this level by sampling the waveform to optimise bunch-to-bunch correlation. Analysis suggests correction capability could be enhanced by firmware waveform integration to achieve a measurable beam stabilisation of ~40 nm in the future.

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29

Murray, Iain. "Application of the Linear-Quadratic model to targeted radionuclide therapy". Thesis, Queen Mary, University of London, 2011. http://qmro.qmul.ac.uk/xmlui/handle/123456789/2684.

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The principal aim of this work was to test the hypothesis that the Linear-Quadratic (LQ) model of cell survival, developed for external beam radiotherapy (EBRT), could be extended to targeted radionuclide therapy (TRT) in order to predict dose-response relationships. The secondary aim was to establish the relevance of particular radiobiological phenomena to TRT and relate these results to any deviations from the response predicted by the LQ Model. Methods: Cancer cell lines were treated with either EBRT or an in-vitro model of TRT. Dosimetry for the TRT was calculated using radiation transport simulations with the Monte Carlo PENELOPE code. Clonogenic as well as functional biological assays were used to assess cell response. Results: Accurate dosimetry for in-vitro exposures of cell cultures to radioactivity was established. LQ parameters of cell survival were established for cancer cell lines reported to be prone to apoptosis, low dose hypersensitivity (LDH) or the bystander effect. For apoptotic cells and cells exhibiting a bystander effect in response to EBRT, LQ parameters were found to be predictive of cell response to TRT. Apoptosis was not found to be a mode of cell death more specific to TRT than to EBRT. Bystander effects could not be demonstrated in cells exposed to TRT. Exposure to low doses of radiation may even protect against the bystander effect. The LQ model was not predictive of cell response in cells previously shown to exhibit LDH. This led to a development of the LQ model based upon a threshold dose-rate for maximum repair. However, the current explanation of LDH may not explain the inverse dose-rate response. Conclusion: The LQ model of cell survival to radiation has been shown to be largely predictive of response to low dose-rate irradiation. However, in cells displaying LDH, further adaptation of the model was required

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30

Jolly, Simon. "An intra-pulse fast feedback system for a future linear collider". Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:3e17d216-7430-4869-9873-4a469fa9c4c5.

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An intra-pulse Interaction Point fast feedback system (IPFB) has been designed for the Next Linear Collider (NLC), to correct relative beam-beam misalignments at the Interaction Point (IP). This system will utilise the large beam-beam kick that results from the beam-beam interaction and apply a rapid correction to the beam misalignment at the IP within a single bunch train. A detailed examination of the IPFB system is given, including a discussion of the necessary electronics, and the results of extensive simulations based on the IPFB concept for fast beam correction are presented. A recovery of the nominal luminosity of the NLC is predicted well within the NLC bunch train of 266 ns. The FONT experiment - Feedback On Nanosecond Timescales - was proposed as a direct test of the IPFB concept and was realised at the NLC Test Accelerator at SLAC. As part of FONT, a novel X-band BPM was designed and tested at the NLCTA. The results of these tests with the NLCTA short and long-pulse beam are presented, demonstrating a linear response to the position of the 180 ns long-pulse beam: measurements show a time constant of ~1.5 ns and a precision of better than 20 microns. A novel BPM processor for use at X-band, making use of the difference-over-sum processing technique, is also presented in detail, with results given for both short and long-pulse beams. The FONT design concepts and modification of the IPFB system for use at the NLCTA are described. The design of a fast charge normalisation circuit, to process the difference and sum signals produced by the BPM processor, forming part of the FONT feedback circuit, is detailed extensively. Bench tests of the feedback electronics demonstrate the effectiveness of the normalisation and feedback stages, for which a signal latency of 11 ns was measured. These bench tests also show the correct operation of the normalisation and feedback principles. Finally, the results of a full beam test of the FONT system are presented, during which a system latency of 70 ns was measured. These rigorous tests establish the soundness of the IPFB scheme and show correction of a mis-steered bunch train within the full NLCTA pulse length of 180 ns.

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31

Silva, Ricardo Goulart da. "Desenvolvimento de um programa de controle da qualidade para a tecnologia VMAT". Universidade Tecnológica Federal do Paraná, 2013. http://repositorio.utfpr.edu.br/jspui/handle/1/727.

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A radioterapia moderna continua evoluindo e trazendo mudanças tecnológicas que envolvem novas modalidades de imagem, novos acessórios de imobilização e novos sistemas para a entrega da dose. Esses avanços possibilitam reduzir a dose recebida pelos tecidos sadios e, consequentemente, diminuem o risco de toxicidade e morbidade. Ao mesmo tempo, maiores doses podem ser prescritas para os volumes tumorais, o que aumenta a probabilidade de controle locorregional. Técnicas tradicionais de IMRT oferecem todas essas vantagens, porém, o tempo de cada sessão de tratamento costuma ser muito longo, principalmente para os casos de cabeça e pescoço. Atualmente, a técnica VMAT é uma realidade em vários centros de referência ao redor do mundo. Essa tecnologia melhorou a eﬁciência na entrega da dose em relação aos tratamentos convencionais de IMRT, diminuindo o tempo de cada aplicação, e apresenta mais graus de liberdade no processo de otimização do tratamento. A modulação dos feixes de radiação é obtida pela variação simultânea de parâmetros dinâmicos como a taxa de dose, velocidade de gantry e a velocidade das lâminas do sistema de colimação. A alta complexidade associada às novas tendências de tratamento, inevitavelmente, exige um maior rigor em relação aos testes de controle da qualidade que devem ser realizados. Os métodos de comissionamento reportados para a tecnologia RapidArc foram estendidos e adaptados para um acelerador Elekta Synergy através de arquivos que podem ser construídos utilizando o software iComCAT. São apresentados testes especíﬁcos para o controle da qualidade da máquina e o processo de validação dosimétrica empregado no sistema de planejamento Monaco. Os parâmetros especíﬁcos de lâmina, modelados através do algoritmo Monte Carlo, foram avaliados e os testes do TG 119 foram adaptados para os planejamentos de VMAT. No ﬁnal é apresentado o programa que foi desenvolvido para o controle da qualidade especíﬁco da tecnologia VMAT em aceleradores Elekta.
Modern radiation therapy keeps evolving and the technological changes include new imaging modalities, new patient immobilization devices and new treatment delivery systems. These advances have made it possible to reduce the dose to normal tissue structures and consequently minimize the risk of toxicity and morbidity, while allowing for dose escalation to the tumor volumes, potencially leading to improved locoregional control. Traditional IMRT techniques offer all of these features but the treatment session time is usually long, mainly for the head and neck cases. Currently, the VMAT technique is a reality in reference centers around the world. This technology has improved delivery efﬁciency over IMRT, decreasing the treatment application time, as this modality introduces extra degrees of freedom in the optimization process. The modulation of the radiation beams is achieved by simultaneous variation of dynamic parameters such as dose rate, gantry speed and leaves speed. The high level of complexity associated to the new treatment trends, inevitably, requires more accuracy and more rigorous quality assurance programs. The commissioning methods reported for the Varian RapidArc system were extended to an Elekta Synergy linear accelerator, using custom ﬁles built in the iComCAT software. Speciﬁc tests for the machine quality assurance are presented and also the dosimetric validation process applied to the Monaco treatment planning system. The MLC parameters, modeled by the Monte Carlo algorithm, were analyzed and the TG 119 tests were adapted for VMATplanning. In the end, a speciﬁc program developed for the VMAT technology for Elekta accelerators is presented.

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32

POLI, MARIA E. R. "Dosimetria aplicada na irradiacao de toda a pele utilizando feixes de eletrons com energia nominal de 4 MeV". reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10813.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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33

Rao, Arati. "Therapeutic strategies for restoring linear growth in children with Crohn's disease". Thesis, Queen Mary, University of London, 2014. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9005.

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Linear growth retardation affects up to 40% of children with Crohn’s disease (CD). It is caused by a combination of under\nutrition, and by a direct effect of cytokines on the axis linking human growth hormone (GH), insulin like growth factor\1 (IGF\1) and the growth plate of growing bones. In particular,the inflammation causes a functional insensitivity to GH, resulting in low circulating IGF\1. Current management is synonymous with the optimal management of childhood CD:to eliminate inflammation,and maintain remission. However, there is currently no consensus as to how to treat growth failure in patients whose inflammation remains intractable to treatment. This thesis examined the hypothesis that successful treatment of inflammation would improve linear growth in children with CD. We performed a series of retrospective studies examining a cohort of children aged ≤17 years with CD treated at Bart’s and The London Children Hospital. We determined the height standard deviation scores (SDS) of patients at diagnosis and investigated growth outcomes following treatments used to induce and maintain remission. These were:exclusive enteral nutrition (EEN), thiopurines and infliximab. Finally, as a potential new therapy, we considered the use of exogenously administered recombinant human IGF\1 (rhIGF\1) to restore plasma IGF\1 levels. We performed an open\labelled pharmacokinetic (PK) study of rhIGF\1 in 8 children with CD and growth failure. 9% of our patients had height SDS of \2 SDS at diagnosis; a four\fold increase compared to the normal age matched population. In addition, symptom duration negatively correlated with height SDS at diagnosis (r=\0.06; p=0.02). From 89 5 patients receiving EEN for primary induction of remission, 62.9% (56/89) of patients achieved complete remission. Over the course of 5 years, responders to EEN grew significantly better than non\responders (change in height SDS +0.18 [0.12] vs to \ 0.37 [0.13] respectively; p=0.005). This occurred despite no differences in duration of remission or treatment escalation between groups. 51% (26/51) patients treated with thiopurines were in remission at 12 months. These patients had improved growth (median change height SDS [IQR] 0.08 [\0.06 – 0.19] vs \0.24 [\0.61 \ \0.07] in non\responders; p=0.001). 39.2% (20/51) of these patients started anti\TNF therapy. However, over 12 months, we found that this conferred no improvement in growth (median [IQR] at 0 months\0.38 [\1.73 to \0.10] as compared to \0.61 [\ 1.72 to \0.09] at 12 months; p=0.43), irrespective of response to treatment. Subcutaneous treatment with 120 μg/kg twice daily rhIGF\1 restored plasma levels of IGF\1 in our patients, albeit it in some to high levels (median [range] concentration +2.09 [\1.27 to +5.21]). We were able to develop a PK mathematical model from these results to determine a more appropriate dosage. We found that in addition to patient’s age and weight, PCDAI also needs to be taken into consideration when determining dose. In summary, growth retardation is very common finding in paediatric CD. Response to EEN and thiopurines seems to result in beneficial effects upon growth. However, a number of children continued to have poor growth despite treatment. Our results show it is possible to increase circulating IGF\1 concentrations with exogenous injections, and develop a mathematical model to devise a dose to use in further trials.

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34

Montanari, Carlo Emilio. "Diffusive approach for non-linear beam dynamics in a circular accelerator". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/19289/.

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Nella fase di design e simulazione di un acceleratore circolare, risulta fondamentale avere una buona comprensione del moto betatronico non-lineare delle singole particelle, e di come questo interferisce con la qualità del fascio. In questo lavoro vengono studiati sistemi Hamiltoniani sottoposti a perturbazioni stocastiche tramite un framework diffusivo, basato sull'equazione di Fokker-Planck. Tale studio viene poi applicato all'analisi del moto betatronico non-lineare e al problema dell'Apertura Dinamica. In particolare, vengono impostate le basi per formulare un metodo di interpolazione di processi diffusivi simil-Nekhoroshev e viene proposta una procedura sperimentale per misurare gli effetti di diffusione locale all'interno di un acceleratore. L'Apertura Dinamica è una quantità chiave per il comportamento a lungo termine di un acceleratore, tuttavia, la misura di questa quantità nelle simulazioni presenta serie difficoltà dal punto di vista computazionale. È dunque nel nostro interesse riuscire a formulare una legge che descriva la dipendenza dal tempo dell'Apertura Dinamica.

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35

TORETI, DALILA L. "Aceite, comissionamento e controle de qualidade em radiocirurgia". reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9479.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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36

FONSECA, GABRIEL P. "Projeto e construcao de placas espalhadoras e degradadoras de energia para uso em radioterapia com feixe de eletrons para doencas de pele". reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9550.

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IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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37

Russman, Felipe Boff. "Quebra de dinâmica ponderomotiva como um eficiente mecanismo de aceleração e focagem de partículas carregadas". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/174847.

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Abstract (sommario):

A presente dissertação estuda a dinâmica uni e tridimensional de uma part cula solitária eletricamente carregada sob a ação de uma onda eletrostática de alta frequência lentamente modulada. A onda dota a partícula de energia potencial elétrica e o seu movimento e conhecido através do emprego do formalismo hamiltoniano, onde se faz a consideração de efeitos relativísticos devido as altas velocidades envolvidas no processo. Enquanto a velocidade máxima experimentada pela partícula permanece suficientemente abaixo da velocidade de fase característica da onda que a acelera, sua dinâmica pode ser bem descrita por uma re nada aproximação ponderomotriz. Com esta abordagem, prevê-se corretamente a velocidade média, máxima e m nima desenvolvida pela partícula ao longo de seu movimento através das curvas que permeiam e envelopam o per l de velocidade. Os limites de validade da aproximação são bem estabelecidos e, uma vez ultrapassados, a partícula com velocidade ressonante e capturada pela onda. Sob as adequadas condições calculadas neste trabalho, o mecanismo de captura instala, espontaneamente, a partícula em fase otima relativa a onda e a acelera a velocidades muito próximas da velocidade da luz no vácuo. Em consonância, o processo de aceleração e otimizado com a focagem da partícula em direção ao eixo de propagação da onda durante um certo intervalo de tempo e de comprimento aproveitáveis.
The present dissertation studies the one and three-dimensional dynamics of an electrically charged solitary particle under the action of a slowly modulated high frequency electrostatic carrier wave. The wave gives the particle electrical potential energy and its movement is known through the use of Hamiltonian formalism, where relativistic e ects are considered due to the high velocities involved in the process. Meanwhile the maximum speed experienced by the particle remains su ciently below the characteristic phase velocity of the accelerating carrier wave, its dynamics can be well described by a re ned ponderomotive approach. With this approach, the average, maximum and minimum speed developed by the particle along its movement through the curves that permeate and envelop the velocity pro le. The limits of validity of the approximation are well established and, once exceeded, the particle with resonant velocity is captured by the wave. Under the appropriate conditions calculated in this work, the capture mechanism spontaneously installs the optimum phase particle relative to the wave and accelerates towards the speed of light in the vacuum. At same time, the acceleration process is optimized by focusing the particle towards the wave propagation axis for a certain usable time interval and length.

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38

Cengiz, Mehmet Ali. "Contributions to the development and analysis of multivariate generalized linear models, with application to the diagnosis of arterial occlusive disease". Thesis, University of Salford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265738.

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39

Lundgren, Maria. "Born Small for Gestational Age : Impact of Linear Catch-up Growth". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl.[distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3563.

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40

Stephenson, John. "Multilevel generalised linear modelling and competing risks multistate survival analysis modelling of childhood caries". Thesis, Cardiff University, 2009. http://eprints.hud.ac.uk/7910/.

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Abstract (sommario):

There has been an ongoing debate regarding appropriate strategies for the management of carious primary teeth. Studies appear to provide evidence that both selective, symptom-based interventions and traditional restorative strategies are advantageous. However, the analysis and quantification of childhood caries may be affected by clustering of data, and the concurrent risk of exfoliation of primary teeth. Multilevel generalised linear models for the occurrence of primary caries were derived utilising data from a cohort study of 2,654 children aged 4-5 years at baseline undertaken 1999-2003. These models, which assumed underlying hierarchies with clustering at child, tooth and surface levels, identified higher rates of caries occurrence in primary molar teeth to be associated with boys, poor socio-economic background, lack of water fluoridation, 2nd mandibular molars and occlusal surfaces. Significant risk factors identified were carried forward for inclusion in parametric competing risks multivariate multilevel survival models, utilising cohort study data augmented with Dental Practice Board treatment data. Analysis of sound teeth and surfaces found the concurrent risk of exfoliation did not alter inferences of parameter significance, but restricted the extent of caries occurrence and reduced distinction in survival experience between different types of teeth and surfaces in children from different demographic backgrounds. Further competing risks survival models were derived to analyse the same teeth and surfaces in the untreated carious and filled states, to assess the effect of restorative treatment on subsequent exfoliation and extraction. Survival rates extrapolated to 14 years without further treatment for filled molar teeth were approximately double those of untreated teeth. Time of caries occurrence and treatment also affected survival, with later occurrence or treatment of caries associated with higher survival rates. However, early filling of carious teeth resulted in the greatest reductions in the expected time that decay is present in the mouth.

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VIEIRA, ANDRÉ M. de M. "Dosimetria dos sistemas de radiocirurgia estereotáxica com aceleradores lineares equipados com colimadores micro multi-lâminas". reponame:Repositório Institucional do IPEN, 2008. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11608.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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42

Tsirakos, Dimitrios Konstantinos. "Biomechanical analysis of a ballistic throwing task under different loading conditions using non-linear optimisation methods". Thesis, Manchester Metropolitan University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266789.

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43

Barons, Martine J. "What is the added value of using non-linear models to explore complex healthcare datasets?" Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/58401/.

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Health care is a complex system and it is therefore expected to behave in a non-linear manner. It is important for the delivery of health interventions to patients that the best possible analysis of available data is undertaken. Many of the conventional models used for health care data are linear. This research compares the performance of linear models with non-linear models for two health care data sets of complex interventions. Logistic regression, latent class analysis and a classification artificial neural network were each used to model outcomes for patients using data from a randomised controlled trial of a cognitive behavioural complex intervention for non-specific low back pain. A Cox proportional hazards model and an artificial neural network were used to model survival and the hazards for different sub-groups of patients using an observational study of a cardiovascular rehabilitation complex intervention. The artificial neural network and an ordinary logistic regression were more accurate in classifying patient recovery from back pain than a logistic regression on latent class membership. The most sensitive models were the artificial neural network and the latent class logistic regression. The best overall performance was the artificial neural network, providing both sensitivity and accuracy. Survival was modelled equally well by the Cox model and the artificial neural network, when compared to the empirical Kaplan-Meier survival curve. Long term survival for the cardiovascular patients was strongly associated with secondary prevention medications, and fitness was also important. Moreover, improvement in fitness during the rehabilitation period to a fairly modest 'high fitness' category was as advantageous for long-term survival as having achieved that same level of fitness by the beginning of the rehabilitation period. Having adjusted for fitness, BMI was not a predictor of long term survival after a cardiac event or procedure. The Cox proportional hazards model was constrained by its assumptions to produce hazard trajectories proportional to the baseline hazard. The artificial neural network model produced hazard trajectories that vary, giving rise to hypotheses about how the predictors of survival interact in their influence on the hazard. The artificial neural network, an exemplar non-linear model, has been shown to match or exceed the capability of conventional models in the analysis of complex health care data sets.

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44

Arthofer, Christoph. "Multi-atlas segmentation using clustering, local non-linear manifold embeddings and target-specific templates". Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/50070/.

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Multi-atlas segmentation (MAS) has become an established technique for the automated delineation of anatomical structures. The often manually annotated labels from each of multiple pre-segmented images (atlases) are typically transferred to a target through the spatial mapping of corresponding structures of interest. The mapping can be estimated by pairwise registration between each atlas and the target or by creating an intermediate population template for spatial normalisation of atlases and targets. The former is done at runtime which is computationally expensive but provides high accuracy. In the latter approach the template can be constructed from the atlases offline requiring only one registration to the target at runtime. Although this is computationally more efficient, the composition of deformation fields can lead to decreased accuracy. Our goal was to develop a MAS method which was both efficient and accurate. In our approach we create a target-specific template (TST) which has a high similarity to the target and serves as intermediate step to increase registration accuracy. The TST is constructed from the atlas images that are most similar to the target. These images are determined in low-dimensional manifold spaces on the basis of deformation fields in local regions of interest. We also introduce a clustering approach to divide atlas labels into meaningful sub-regions of interest and increase local specificity for TST construction and label fusion. Our approach was tested on a variety of MR brain datasets and applied to an in-house dataset. We achieve state-of-the-art accuracy while being computationally much more efficient than competing methods. This efficiency opens the door to the use of larger sets of atlases which could lead to further improvement in segmentation accuracy.

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GONCALVES, VINICIUS D. "Caracterização da dose em pacientes devido a produção de imagem de raios-X utilizadas em radioterapia guiada por imagem - IGRT". reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10555.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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46

Rosencranz, Daniela Necsoiu. "Monte Carlo simulation and experimental studies of the production of neutron-rich medical isotopes using a particle accelerator". Thesis, University of North Texas, 2002. https://digital.library.unt.edu/ark:/67531/metadc3077/.

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Abstract (sommario):

The developments of nuclear medicine lead to an increasing demand for the production of radioisotopes with suitable nuclear and chemical properties. Furthermore, from the literature it is evident that the production of radioisotopes using charged-particle accelerators instead of nuclear reactors is gaining increasing popularity. The main advantages of producing medical isotopes with accelerators are carrier free radionuclides of short lived isotopes, improved handling, reduction of the radioactive waste, and lower cost of isotope fabrication. Proton-rich isotopes are the result of nuclear interactions between enriched stable isotopes and energetic protons. An interesting observation is that during the production of proton-rich isotopes, fast and intermediately fast neutrons from nuclear reactions such as (p,xn) are also produced as a by-product in the nuclear reactions. This observation suggests that it is perhaps possible to use these neutrons to activate secondary targets for the production of neutron-rich isotopes. The study of secondary radioisotope production with fast neutrons from (p,xn) reactions using a particle accelerator is the main goal of the research in this thesis.

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47

Choudhury, Tisha. "Delineating key genetic components on linear plasmid 36 that contribute to its essential role in Borrelia burgdorferi mammalian infectivity". Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5916.

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The spirochete Borrelia burgdorferi is the etiologic agent of Lyme disease. This pathogen has a complex enzootic life cycle that involves passage between the tick vector (Ixodes scapularis) and various vertebrate hosts with humans being inadvertent hosts. There is a pressing need to study the genetic aspects of the B. burgdorferi infectious cycle and particularly spirochete genes involved in mammalian infectivity so as to develop novel therapeutic and diagnostic strategies to combat Lyme disease. The B. burgdorferi genome is fragmented and comprised of a single 900 kb linear chromosome and multiple linear and circular plasmids. It has been observed that plasmids are lost during serial passage and manipulation in vitro and the loss of some of the plasmids has been shown to be related to the loss of infectivity and persistence in the host. One such plasmid is linear plasmid 36 (lp36). lp36 is approximately 36kb in size and carries 56 putative open reading frames a majority of which have no predicted function. B. burgdorferi lacking lp36 show no deficiency in survival in ticks; however, these mutant spirochetes are highly attenuated for mammalian infectivity. The genetic components of this plasmid that contribute to its function in mammalian infectivity have yet to be clearly defined. Using an in vivo expression technology (IVET) based genetic screen the lp36-encoded gene bbk46 was identified as a candidate B. burgdorferi gene that is expressed during mammalian infection. Herein we present evidence that bbk46 is required for B. burgdorferi persistent infection of immunocompetent mice. Our data support a molecular model of immune evasion by which bbk46 functions as an RNA to regulate expression of the antigenic variation protein VlsE. These data represent the first demonstration of a regulatory mechanism critical for controlling vlsE gene expression. Moreover these findings further define the critical role of linear plasmid 36 in Borrelia burgdorferi pathogenesis.
Ph.D.
Doctorate
Molecular Biology and Microbiology
Medicine
Biomedical Sciences

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48

Arpad, Tot. "Karakterizacija fotona i neutrona megavoltažnih terapijskih akceleratora". Phd thesis, Univerzitet u Novom Sadu, Prirodno-matematički fakultet u Novom Sadu, 2018. https://www.cris.uns.ac.rs/record.jsf?recordId=107144&source=NDLTD&language=en.

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Poznavanje spektra x-zračenja kao i drugih osobina je od izuzetnog značaja kako za planiranje radijacione terapije tako i sa aspekta zaštite pacijenta i osoblja. Takođe, poznavanje svojstava neutrona nastalih u interakciji fotona sa materijalimaoko akceleratora, je od izuzetnog značaja sa dozimetrijskog aspekta. Poslednjih godina sve se više upotrebljavaju linearni akceleratori bez homogenizacionog filtera tzv. FFF (Flatteninig Filter Free), a kako su karakteristike snopa u toma načinu rada akceleratora još uvek nedovoljno ispitane, njima smo posvetili posebnu pažnju. Urađena su i detaljna dozimetrijska merenja fotona kako u radu sa homogenizacionim filterom (FF) tako i bez njega (FFF), kao i dozimetrijsko merenje neutrona. Direktno merenje samogspektra nekim od detektora (NaI ili HPGe) nije moguće zbog visokih intenziteta stoga smo u radu koristili indirektne metode i to aktivacionu analizu i atenuacionu analizu.Urađena su detaljna dozimetrijska merenja ekvivalentne doze neutrona u terapijskoj sobi sa dva zaokreta hodnika i na osnovu rezultata predložena je korekcija metode za izračunavanje neutronske doze na ulaznim vratima. Fotoaktivacionimmerenjima, gde su se u oba načina rada terapijskog akceleratora pratile aktivnosti izomera ^115m In, ustanovljeno je da se kod dva tipa akceleratora (Elekta Versa HD, Varian TrueBeam) oblik spektra u visokoenergetskom delu znatno razlikuje, kao i da postoji razlika u obliku spektra na ivici polja i u njegovoj sredini. Atenuacionom analizom na osnovu standardnog metoda rekonstrukcije fotonskog spektra putem Laplasovih transforma, dobijene su izvesne razlike u oblicima spektara za dva režima rada. Takođe, rekonstrukcijom spektra putem odabira parametara korekcine funkcije koja bi teorijski oblik spektra (Šifova funkcija) trebao da prevede u realan spektar za oba režima rada dobijene su izvesne razlike u oblicima spektra. Dozimetrijska merenja fotonske doze na ulaznim vratima terapijske sobe sa jednim zaokretom, sa i bez homogenizacionog filtera za različite veličine polja i sa i bez vodenog kanistera koji simulira pacijenta u snopu, pokazuju da je izmerena doza na ulaznim vratima u FFF modu rada uvek niža od izmerene doze u slučaju da se koristi homogenizacioni filter.
Knoweledge of the x-ray spectrum as well as other characteristics of the beam is of great importance both for the planning of radiotherapy as well as for the protection of patients and staff. Also, the knowledge of the neutron properties generated in the interaction of photons with materials around the accelerator is of great importance from the dosimetric aspect. In recent years, linear accelerators are increasingly used without a flattening filter, so-called FFF (Flatteninig Filter Free), and as the characteristics of the beam in this mode of operation of the accelerator are still insufficiently investigated, we paid special attention to them. Detailed dosimetric measurements of photons were performed both with (FFF) and without the flattening filter (FF), as well as the dosimetric measurement of the neutron. Direct measurement of the spectrum itself by detectors (NaI or HPGe) is not possible due to high intensities, therefore, we used indirect methods in this work, both activation analysis and attenuation analysis. Detailed dosimetric measurements of the neutron equivalent dose in the therapeutic room with two band maze were made and based on the results, correction of the method for calculating the neutron dose at the entrance door was proposed. It was found by photoactivation measurements, where the activities of the isomer ^115mIn were investigated, that in the two types of accelerators (Elekta Versa HD, Varian TrueBeam) the spectrum shape in the high-energy part is significantly different, and that there is a spectrum difference in the edge of the field and in the middle of the field. Attenuation analysis, based on the standard method of reconstructing the photon spectrum through Laplace transforms, showed some differences in the spectra of the two working modes of accelerators. Also, by reconstructing the spectrum by correction function that should transform the theoretical spectrum form (the Schiff function) into a real spectrum for both modes of operation, certain differences in spectrum shapes were obtained. Dosimetric measurements of the photon dose at the entrance door of treatment room with a single maze with and without a homogenizing filter for different field sizes and with and without a water canister which simulates the patient in a beam showed that the measured dose at the entrance door in the FFF mode is always lower than the measured doses in FF mode.

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TERREMOTO, LUIS A. A. "Eletrodesintegração do sup(232)Th por emissão de um nêutron". reponame:Repositório Institucional do IPEN, 1986. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11629.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Fisica, Universidade de Sao Paulo - IF/USP

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50

Wang, Ling, Yujia Wang, Juan Zhao, Junping Ren, Kenton H. Hall, Jonathon P. Moorman, Zhi Q. Yao e Shunbin Ning. "The Linear Ubiquitin Assembly Complex Modulates Latent Membrane Protein 1 Activation of NF-κB and Interferon Regulatory Factor 7". Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/6529.

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Recently, linear ubiquitin assembly complex (LUBAC)-mediated linear ubiquitination has come into focus due to its emerging role in activation of NF-κB in different biological contexts. However, the role of LUBAC in LMP1 signaling leading to NF-κB and interferon regulatory factor 7 (IRF7) activation has not been investigated. We show here that RNF31, the key component of LUBAC, interacts with LMP1 and IRF7 in Epstein-Barr virus (EBV)-transformed cells and that LUBAC stimulates linear ubiquitination of NEMO and IRF7. Consequently, LUBAC is required for LMP1 signaling to full activation of NF-κB but inhibits LMP1-stimulated IRF7 transcriptional activity. The protein levels of RNF31 and LMP1 are correlated in EBV-transformed cells. Knockdown of RNF31 in EBV-transformed IB4 cells by RNA interference negatively regulates the expression of the genes downstream of LMP1 signaling and results in a decrease of cell proliferation. These lines of evidence indicate that LUBAC-mediated linear ubiquitination plays crucial roles in regulating LMP1 signaling and functions. IMPORTANCE We show here that LUBAC-mediated linear ubiquitination is required for LMP1 activation of NF-κB but inhibits LMP1-mediated IRF7 activation. Our findings provide novel mechanisms underlying EBV-mediated oncogenesis and may have a broad impact on IRF7-mediated immune responses.

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Tesi sul tema "Linear accelerators in medicine"

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