A Radiological Dispersal Device (RDD) is any device that releases radioactive material into the environment (e.g. Dirty Bomb). Depending on the size of the explosion, location, and the weather conditions the affected area could be several city blocks. In such an event there could be hundreds, even thousands of contaminated victims seeking medical treatment. One concern in the healthcare industry is the uncertainty of the level of radiation exposure to the healthcare providers from these contaminated patients. The intention of this study is to estimate the levels of skin contamination for victims arriving at the hospital needing conventional medical treatment. Given a skin contamination of the victim the effective dose rate to the healthcare providers can be estimated in certain scenarios. The effective dose rate will determine how long the healthcare provider would be able to care for the victims.

Doctor of Health Science / An investigation of clinical Abdominal Computed Tomography (CT)dose, and associated clinical diagnostic protocols, has been ndertaken. This research was carried out to study the pattern of CT dose from routine abdominal examinations in Malaysian practices. From this study it is hoped to establish a Dose Reference Level (DRL) to assist in optimising radiation dose for CT abdominal examination in Malaysia

Os receptores de imagem radiográfica digitais estão gradualmente substituindo os sistemas tela-filme em radiodiagnóstico. Atualmente a radiografia computadori- zada (CR - Computed Radiography) é a modalidade digital mais comum em muitos serviços de radiodiagnostico. E baseada na utilização de fósforos foto estimuláveis, que também são conhecidos como fósforo de armazenamento. Quando sistemas tela-filme são utilizados como receptores de imagem, uma dose de radiação inadvertidamente alta no paciente irá resultar em um filme escuro, que fornece feedback imediato para o técnico em radiologia quanto aos fatores de técnica utilizados e a dose relativa. No entanto, quando receptores de imagem digitais são usados, uma dose alta no paciente pode produzir imagens excelentes o que resulta em uma tendência de se utilizar doses mais elevadas do que o necessário. A adequada justificação e otimização dos procedimentos exige o conhecimento dos valores típicos de dose em pacientes em um determinado serviço de radiodiagnóstico. O termo índice de exposição refere-se à dose absorvida na placa fósforo. Após a leitura da imagem com um sistema de laser o histograma dos sinais é computado e o índice de exposição é determinado com base nos valores dos pixels (picture elements) usando uma relação logarítmica. Os fabricantes dos sistemas de CR oferecem os índices de exposição como um salvaguarda contra doses altas, mas a base para os valores recomendados não é clara. Além disso, os índices de exposição não estão diretamente relacionados com a dose no paciente. O objetivo deste trabalho foi estabelecer um método indireto para calcular os valores de dose de entrada em pacientes submetidos a exames diagnósticos em sistemas de raios X com CR com base no índice de exposição. / The receptors of digital radiography image are gradually substituting the screen-film systems in radiodiagnostic. Currently, computed radiography is the most common method in many radiography services. It is based in the application of photostimulable phosphorus, that are also known as phosphorus storage. When screen-film systems are utilized as image receptors, an inadvertently high dose of radiation in the patient will result in a dark film screen, that inputs immediate feedback to the radiology technician as to the technical factors utilized and the relative dose. However, when digital image receptors are used, a high dose in the patient can produce excelent images which re-sult in a tendency of using higher doses than necessary. The adequate extenuation and optimization of the procedures demand the knowledge of the characteristic dose values in patients in a determined radiodiagnostic service. The term exposure index refers to the absorbed dose in the phosphorus plate. Following the image reading with a laser system the histogram of signs is computed and the exposure index is determi-ned in the basis of picture elements using a logarithmic relationship. The manufacturer of the systems of pixels offer the exposure indexes as a safeguard against high doses, but the basis for the recommended values are not clear. Moreover, the exposure indexes are not directly related to the dose in patients. The aim of this work was to establish an indirect method to estimate the values of entrance doses in patients who have undergone diagnostic exams in X ray systems with computed radiography based on exposure indexes. The values of entrance doses obtained were compared with the values also obtained indirectly based in the measurements of the X ray tubes output.

O processo de radioterapia consiste em várias etapas, iniciando na indicação pelo médico. O plano de tratamento passa então por um processo denominado simulação, onde é adquirida uma série de imagens por tomografia computadorizada que são transferidas para o sistema de planejamento, onde a delineação dos volumes alvos e tecidos normais adjacentes serão realizadas. Após a delineação desses volumes, no sistema de planejamento são colocados os campos de irradiação e a dose desejada conforme prescrição médica. O sistema de planejamento calcula então a dose que o volume alvo e os tecidos adjacentes poderão receber. Se estas doses estão dentro dos padrões aceitáveis, o planejamento então é aprovado e enviado ao acelerador linear para a execução do tratamento. Antes da execução do tratamento, é realizada uma imagem, seja através de filme radiográfico ou digitalmente, para avaliar a posição no paciente na mesa de tratamento. Se a localização do paciente está correta, a dose é então liberada. Esse protocolo de aquisição de imagem é denominado como Radioterapia Guiada por Imagem (IGRT). A quantidade de radiografias de posicionamento segue um protocolo definido conforme a região a ser irradiada. Como resultado deste procedimento, sabe-se que uma determinada dose adicional é recebida pelos pacientes, tornando-se um fator importante a ser determinado. Esta avaliação foi realizada através da simulação de Monte Carlo, utilizando o código MCNP. Para isso foi realizada primeiramente toda a caracterização da fonte de raios X com uso de câmaras de ionização e dosimetros TL juntamente com as simulações no MCNP. Após essa caracterização, as imagens e as estruturas do planejamento radioterápico foram convertidas para serem utilizadas no código MCNP. Para que as doses fossem calculadas nos principais órgãos de risco no tratamento de próstata: bexiga, reto e cabeças de fêmur direita e esquerda. / The process of radiotherapy treatment consists of several stages, starting from the statement given by the physician. The treatment planning undergoes a process called simulation, where a series of computed tomography images is acquired and transferred to the treatment planning system, where the delineation of target volumes and adjacent normal tissues will be performed. After the delineation of these volumes, then irradiation fields and dose precribed by the physician are placed in the treatment planning system. It calculates the dose that target volume and surrounding tissues are receiving. If the doses are within acceptable standard values, then the design is approved and submitted to the linear accelerator for the treatment course. Before treatment course, an image is performed, either by radiographic or digital film, in order to evaluate (check) the patient position on the treatment table. If the patient position is correct, the treatment is realized. This image acquisition protocol is called Image-Guided Radiotherapy (IGRT). The amount of radiographic positioning follow a protocol defined for the region to be treated. As a result of this procedure, it is known that a specific additional dose is received by the patient, becoming an important factor to be determined. In this work, this additional dose evaluation was performed by the Monte Carlo simulation using the MCNP algorithm. The characterization of the entire X-ray source was primarily realized with ionization chamber thermoluminescent dosimeters and simulations with the MCNP code. After the X-ray tube characterization, images and the structures for the radiotherapy planning were converted to be used in the MCNP code for dose calculation at the main organs at risk during a prostate treatment: bladder, rectum and femoral heads right and left.

Les protocoles de traitement du cancer par Radiothérapie Conformationnelle par Modulation d'Intensité (RCMI) ciblent avec une précision de plus en plus grande la tumeur. Pour cela, ils nécessitent des informations anatomiques précises du patient juste avant le traitement, qui peuvent d'être obtenues à l'aide de systèmes d'imagerie embarqués sur l'accélérateur linéaire médical délivrant le faisceau de traitement. Ces systèmes, composés d'un tube à rayons X et d'un détecteur 2D planaire, sont appelés kV-Cone Beam CT (kV-CBCT). Aujourd'hui, leur usage est très fortement répandu dans le cadre des traitements par RCMI. Cependant, ces examens kV-CBCT sont responsables d'une dose de rayonnements ionisants additionnelle qui est loin d'être négligeable et pouvant d'être à l'origine de l'apparition d'effets secondaires, tels que des cancers radio-induits chez les patients traités. Au cours de cette thèse, un simulateur basé sur la méthode de Monte-Carlo a été développé permettant ainsi d'estimer avec précision les doses délivrées aux organes lors des examens d'imagerie kV-CBCT. Cet outil a ensuite été utilisé afin d'étudier différentes stratégies de prise en compte clinique de ces doses additionnelles. L'étude présentée dans ce manuscrit propose notamment une méthode rapide d'estimation des niveaux de doses délivrés aux organes prenant en compte la morphologie de chaque patient. Cette stratégie a été développée à partir d'une cohorte de 50 patients incluant 40 enfants et 10 adultes. Ces travaux ont été réalisés en collaboration avec l'unité de physique médicale du Centre Eugène Marquis à Rennes qui a fourni les données cliniques nécessaires à l'étude. / Protocols for cancer treatment using intensity-modulated radiation therapy (IMRT) allow to target the tumor with an increased precision. They require accurate anatomical information of the patient just before the treatment, which can be obtained using on-board imaging systems mounted on the medical linear accelerator delivering the treatment beam. These systems, composed of an X-ray tube and a 2D planar detector, are called kV-Cone Beam CT (kV-CBCT). Nowadays, they are widely used in the context of IMRT treatments. However, these kV-CBCT examinations are also responsible for an additional dose of ionizing radiations which is far to be negligible and could be the cause for secondary effects, such as radiation-induced second cancers for treated patients. During this PhD work, a simulator based on the Monte Carlo method was developed in order to calculate accurately the doses delivered to organs during kV-CBCT examinations. Then, this tool was used to study several strategies to take in account for the imaging additional doses in clinical environment. The study reported here includes, in particular, a fast and personalized method to estimate the doses delivered to organs. This strategy was developed using a cohort of 50 patients including 40 children and 10 adults. This work has been done in collaboration with the medical physics unit of the Eugène Marquis medical center in Rennes, which has collected the clinical data used for this study.

The dose-effect relationship in psychotherapy has been examined extensively, but few studies have included session frequency as a component of psychotherapy "dose." Those studies that have examined the effects of session frequency have indicated that it may affect both the total amount of recovery and the speed of recovery. No studies were found examining the clinical significance of this construct in a naturalistic setting. The change trajectories of 16,003 clients were examined using multi-level modeling and including session frequency as a fixed effect. Of these clients, subgroups were identified that were scheduled approximately once a week or approximately once every two weeks. These groups were compared to each other for differences in speed of recovery and clinically significant change. Results indicated that more frequent therapy was associated with steeper recovery curves. When comparing groups scheduled once a week to those scheduled once every two weeks, more clinically significant gains were identified in those attending once a week, and more significant deterioration was identified in those attending once every two weeks. These findings are discussed in light of the existing literature and the implications for future psychotherapy research and clinical practice.

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