Masters Research - Masters of Philosophy / INTRODUCTION: Level III dosimetric intercomparison studies test the entire radiotherapy patient treatment chain from diagnostic imaging to treatment delivery and verification imaging at multiple radiotherapy centres. The anthropomorphic phantom employed in an intercomparison needs to meet specific criteria including portability, tissue equivalence and accommodation of radiation detectors to ensure clinical relevance and dosimetric accuracy. The proposition that a purpose-built phantom can encompass all the attributes necessary for precise Level III dosimetric intercomparisons for prostate cancer is the premise of this body of work. METHODS: Organ outlines were generated from a human computed tomography image set and incorporated into the phantom design to replicate human anatomy as closely as possible. Twenty-five points of interest were located throughout the dataset to identify where point-dose values could be measured with thermoluminescence dosimeters. The centre of the prostate was identified as the location for measurement with a small-volume ionization chamber. The materials used in this phantom were tested against water to determine relative attenuation, density and Hounsfield Units. Three materials were chosen to mimic bone, organs, and a backfill material and the phantom was manufactured using modern prototyping techniques into five separate coronal slices. Time lines and resource requirements for the phantom design and manufacture were recorded. The ability of the phantom to mimic the entire treatment chain was tested at the Calvary Mater Newcastle Hospital. RESULTS: The phantom CT images indicated the densities and organ geometries were comparable to the original patient. The phantom proved simple to load for dosimetry and rapid to assemble. Measurements indicated the reproducibility to be in the order of 1% for the ionization chamber measurement and within 3% for thermoluminescence dosimeters. Due to heat release during manufacture, small airgaps were present throughout the phantom producing artifacts on lateral images. The overall cost for production of the prototype phantom was comparable to other commercial anthropomorphic phantoms ($AU45,000). The phantom was shown to be suitable for use as a “patient” to mimic the entire treatment chain for typical external beam radiotherapy for prostate and rectal cancer. Outlining of relevant structures by a radiation oncologist was uncomplicated and the computerised treatment plan compared well with the dose measured using ionisation chambers and thermoluminescence dosimeters. DISCUSSION & CONCLUSIONS: The phantom constructed for the present study incorporates all characteristics necessary for accurate Level III intercomparison studies and will be an effective tool for an intercomparison of pelvic treatments in Australasia. These results may benefit analysis of outcomes for prostate cancer treatments, especially in the clinical trial environment. It will be of significant interest in the future to use the phantom to assess advanced radiotherapy delivery techniques such as Intensity Modulated Radiation Therapy (IMRT).

Master of Science / Department of Mechanical and Nuclear Engineering / William L. Dunn / Neutron dosimeters measure neutron doses but portable, real time, high efficiency, and gamma insensitive neutron dosimeters are not commonly available. Characterization of a newly invented neutron dosimeter, based on perforated semiconductor neutron detectors (SNDs) whose perforations are filled with neutron reactive material, was the main purpose of this research study. The characterization procedure was performed by both simulation and experiment. The Monte Carlo N-Particle (MCNP) transport code was used to model a boron-filled dosimeter and to study the responses when the dosimeter was located on the surfaces of a water phantom and an anthropomorphic phantom for parallel beams of neutrons having various energy spectra. A pair of detectors was modeled: one bare and one Cd-filtered. Dosimeter responses were normalized for a beam that would produce 1 mSv ambient dose equivalent if incident on the ICRU sphere phantom. Dosimeter responses were estimated at different positions on the torso and it was found that the responses are relatively insensitive to the placement on the torso. For 100% efficient detectors and for beam with a Watt spectrum incident from front to back of the phantom, the bare detector produces about 140 counts per [Mu]Sv and the Cd-filtered detector produces about 80 counts per [Mu]Sv. The experimental characterization study involves observing SND counts with the dosimeter placed on an anthropomorphic torso phantom and determining the corresponding neutron dose. A TLD pair method was used to determine the neutron dose on the surface of the phantom. The neutron reactive material of the dosimeter was [superscript]6LiF, which is different from that assumed for the modeled dosimeter. A bare dosimeter response collected over 10 min was 25113 [plus or minus] 158 counts and the corresponding neutron dose was measured to be 2.57 mSv. The Cd-filtered dosimeter response collected over 10 min was 23886 [plus or minus] 155 counts and the corresponding neutron dose was measured to be 2.32 mSv. The neutron dosimeters are capable of detecting doses in the [Mu]Sv range and above, and are anticipated to provide direct read-out in dose units in future using count-to-dose conversion factors for bare and Cd-filtered SNDs.

Anthropomorphic phantoms are commonly used for testing radiation fields without the need to expose human subjects. One of the most widely known is RANDO phantom. This phantom is used primarily for medical X-ray applications, but a similar design known as "MATROSHKA" is now being used for space research and exposed to heavy ion irradiations from the Galactic environment. Since the radiation field in the phantom should respond in a similar manner to how it would act in human tissues and organs under an irradiation, the tissue substitute chosen for soft tissue and the level of complexity of the entire phantom are crucial issues. The phantoms, and the materials used to create them, were developed mainly for photon irradiations and have not been heavily tested under the conditions of heavy ion exposures found in the space environment or external radiotherapy. The Particle and Heavy-Ion Transport code System (PHITS) was used to test the phantoms and their materials for their potential as human surrogates for heavy ion irradiation. Stopping powers and depth-dose distributions of heavy charged particles (HCPs) important to space research and medical applications were first used in the simulations to test the suitability of current soft tissue substitutes. A detailed computational anthropomorphic phantom was then developed where tissue substitutes and ICRU-44 tissue could be interchanged to verify the validation of the soft tissue substitutes and and determine the required level of complexity of the entire phantom needed to achieve a specified precision as a replacement of the human body. The materials tested were common soft tissue substitutes in use and the materials which had a potential for the soft tissue substitute. Ceric sulfate dosimeter solution was closest to ICRU-44 tissue; however, it was not appropriate as the phantom material because it was a solution. A150 plastic, ED4C (fhw), Nylon (Du Pont Elvamide 8062), RM/SR4, Temex, and RW-2 were within 1% of the mean normalized difference of mass stopping powers (or stopping powers for RW-2) when compared to the ICRU-44 tissue, and their depth-dose distributions were close; therefore, they were the most suitable among the remaining solid materials. Overall, the soft tissue substitutes which were within 1% of ICRU-44 tissue in terms of stopping power produced reasonable results with respect to organ dose in the developed phantom. RM/SR4 is the best anthropomorphic phantom soft tissue substitute because it has similar interaction properties and identical density with ICRU-44 tissue and it is a rigid solid polymer giving practical advantages in manufacture of real phantoms.

The optimisation of image quality in medical imaging techniques is a significant factor in favourable patient prognoses. The number of counts in a nuclear medicine image is one factor in determining the diagnostic value of the image. The current study aims to determine the variation in counts in whole-body bone scan images with patient height and weight. Three separate studies were undertaken as part of the investigation. First, 65 whole-body bone scans were analysed together with patient height, weight, age and sex. Weight was found to the most important anatomy influence on image counts. However, significant influences from patient sex and age meant that a useful relationship between image counts and patient anatomy based solely on height and weight could not be determined. For the second study, a model of General Electric Millennium MG gamma camera was created and validated within the SIMIND Monte Carlo software. The results indicate that the model is an accurate representation of the gamma camera. Third, the 4D NCAT whole-body patient phantom was modified to represent the average male and female clinical study participants. The phantoms were used in conjunction with the gamma camera model to simulate the whole-body bone scan procedure. The counts in the simulated images were consistent with the average measured counts of the clinical study indicating that it is feasible to use the NCAT phantom for nuclear medicine bone imaging. However, the phantom’s method of activity distribution should be refined to allow a more realistic distribution of activity throughout the skeleton.

After a radiation dispersion device (RDD) event, there may be internally and/or externally contaminated victims. After the RDD event, victims may require immediate medical assistance prior to decontamination. The dose rates to which a healthcare provider is exposed due to the internal and external contamination of the victim were computed using Monte Carlo simulations and five anthropomorphic phantoms. The dose rates to which the victim is exposed due to his/her own external contamination were also computed. For the external contamination modeling, the contamination is assumed to be distributed over the entire exterior of the victimâ s body. The geometrical models of the human body were based on the MIRD stylized phantom. The specific isotopes considered were 60Co, 137Cs, 131I, 192Ir, and 241Am. The surface contamination was generated by creating a 2-mm thick layer adjacent to the outside of the skin of the victim and uniformly sampling the emissions of the radioactive sources throughout this volume. The attending healthcare provider was assumed to be standing 20 cm from mid-torso of the victim. The organ absorbed doses in both the contaminated individual and a healthcare professional were computed. The effective dose to the victim and the attending healthcare professional were computed using the tissue weighting factors in ICRP Publication 60. For example, the dose rate to a reference male healthcare provider from the victim six hours after the inhalation of one ALI by an adipose male victim will be 0.277 mSv/hr. In addition, the air kerma was computed at different distances from the surfaces of the victim phantom and ratios were generated for the air kerma and the effective dose due to the victim from the surface contamination on the victim.

The optimisation of image quality in medical imaging techniques is a significant factor in favourable patient prognoses. The number of counts in a nuclear medicine image is one factor in determining the diagnostic value of the image. The current study aims to determine the variation in counts in whole-body bone scan images with patient height and weight. Three separate studies were undertaken as part of the investigation. First, 65 whole-body bone scans were analysed together with patient height, weight, age and sex. Weight was found to the most important anatomy influence on image counts. However, significant influences from patient sex and age meant that a useful relationship between image counts and patient anatomy based solely on height and weight could not be determined. For the second study, a model of General Electric Millennium MG gamma camera was created and validated within the SIMIND Monte Carlo software. The results indicate that the model is an accurate representation of the gamma camera. Third, the 4D NCAT whole-body patient phantom was modified to represent the average male and female clinical study participants. The phantoms were used in conjunction with the gamma camera model to simulate the whole-body bone scan procedure. The counts in the simulated images were consistent with the average measured counts of the clinical study indicating that it is feasible to use the NCAT phantom for nuclear medicine bone imaging. However, the phantom’s method of activity distribution should be refined to allow a more realistic distribution of activity throughout the skeleton.

Le travail décrit dans cette thèse porte sur l’évaluation du mode d’exposition externe et interne au xénon-133. Ce radionucléide est un des principaux produits de fission du combustible des réacteurs nucléaires. En cas de défaut de gaine combustible, le xénon-133 peut potentiellement exposer le personnel lors de ses interventions dans le bâtiment réacteur. En dosimétrie, les simulations Monte-Carlo sont des outils adaptés pour simuler le transport des rayonnements ionisants dans la matière. A partir des critères de radioprotection actuels, nous avons développé de nouvelles méthodes afin d’améliorer notre compréhension de l’exposition externe et interne auxénon-133 à l’intérieur d’un bâtiment réacteur. Ces nouvelles approches sont basées sur l’utilisation d’un fantôme anthropomorphe, d’une géométrie réaliste de bâtiment réacteur, de simulations Monte-Carlo GEANT4 et de modèles en compartiments. L’exposition externe dans un bâtiment réacteur a été menée en retenant un scénario d’exposition réaliste et conservatif. Nous avons quantifié le débit de dose efficace et le débit de dose équivalente au cristallin. L’exposition interne se produit lorsque le xénon-133 est inhalé. Les poumons sont les premiers organes exposés par l’inhalation du xénon-133, leur débit de dose équivalente a été quantifié. Un modèle biocinétique a été utilisé pour évaluer l’exposition interne au xénon-133. Cette thèse a permis de quantifier les grandeurs dosimétriques liées aux modes d’exposition externe et interne au xénon-133, d’étudier l’impact des changements de limites dosimétriques introduits par la Commission Internationale de Radioprotection prochainement retranscrits dans la réglementation française, et de comprendre la cinétique du xénon-133 dans le corps humain. Nous avons montré que les grandeurs dosimétriques sont nettement inférieures aux limites dosimétriques de la réglementation actuelle et future. / The work described in this thesis focuses on the external and internal dose assessment to xenon-133. During the nuclear reactor operation, fission products and radioactive inert gases, as ¹³³Xe, are generated and might be responsible for the exposure of workers incase of clad defect.Particle Monte Carlo transport code is adapted inradioprotection to quantify dosimetric quantities.The study of exposure to xenon-133 is conducted byusing Monte-Carlo simulations based on GEANT4, ananthropomorphic phantom, a realistic geometry of thereactor building, and compartmental models.The external exposure inside a reactor building isconducted with a realistic and conservative exposurescenario. The effective dose rate and the eye lensequivalent dose rate are determined by Monte-Carlosimulations. Due to the particular emission spectrum ofxenon-133, the equivalent dose rate to the lens of eyesis discussed in the light of expected new eye doselimits.The internal exposure occurs while xenon-133 isinhaled. The lungs are firstly exposed by inhalation, andtheir equivalent dose rate is obtained by Monte-Carlosimulations. A biokinetic model is used to evaluate theinternal exposure to xenon-133.This thesis gives us a better understanding to thedosimetric quantities related to external and internalexposure to xenon-133. Moreover the impacts of thedosimetric changes are studied on the current andfuture dosimetric limits. The dosimetric quantities arelower than the current and future dosimetric limits.

Orientador: Diana Rodrigues Pina / Resumo: A Radiologia Intervencionista (RI) é a área da medicina que proporciona as maiores exposições ocupacionais. Os valores de dose aos quais os intervencionistas são expostos são difíceis de padronizar. Nesta pesquisa apresentamos uma avaliação completa das exposições ocupacionais e determinamos a eficiência de distintos métodos de dosimetria pessoal utilizados na RI. Essa pesquisa foi abordada em 2 etapas, conforme descrito a seguir: A primeira etapa se baseou em caracterizar as exposições ocupacionais em diferentes modalidades de procedimentos de RI vascular para duas categorias de profissionais e estimar o número de procedimentos anuais que cada profissional pode realizar sem exceder os limites de dose. Foi avaliada a exposição ocupacional, através de dosimetria termoluminescente, em diferentes partes do corpo (cristalino, tireoide, tórax, abdômen, pés e mãos) de duas categorias de intervencionistas (principais e assistentes) em três modalidades diferentes de procedimentos de RI vascular. As maiores doses equivalentes foram encontradas para as mão de ambos os profissionais, podendo chegar a aproximadamente 9 mSv em um único procedimento. Algumas regiões dos profissionais em alguns procedimentos podem receber, durante o ano, níveis de doses perigosamente perto dos limites anuais. Dosímetros posicionados no tórax podem subestimar as doses para outras regiões do corpo, especialmente abdômen, extremidades e cristalinos. Na segunda etapa foram avaliadas as eficiências de 6 diferent... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Interventional Radiology (IR) is the area of medicine that provides the largest occupational exposures. The dose values to which interventionists are exposed are difficult to standardize. In this research we present a complete evaluation of occupational exposures and determine the efficiency of different personal dosimetry methods used in IR. This research was performed in 2 stages, as described below: The first step was to characterize the occupational exposures in different modalities of vascular IR procedures for two categories of professionals. We also estimated the number of annual procedures that each professional can perform without exceeding the dose limits. Occupational exposures were evaluated in different body parts (crystalline, thyroid, thorax, abdomen, feet and hands) by two interventional categories (primary and assistants) in three different modalities of vascular IR procedures. The highest equivalent doses were found for the hands of both professionals, reaching approximately 9 mSv in a single procedure. Some regions of professionals in some procedures may receive dose levels during the year dangerously close to annual limits. Dosimeters positioned in the chest may underestimate the doses to other regions of the body, especially the abdomen, extremities and crystalline. The second stage, we evaluated the efficiencies of 6 different personal dosimetry methodologies used internationally to estimate the effective dose received by interventional professionals. An... (Complete abstract click electronic access below) / Mestre

The detonation of a radiological dispersion device (RDD) may result in a situation where many individuals are exposed to contamination due to the inhalation of radioactive materials. Assessments of contamination may need to be performed by emergency response personnel in order to triage the potentially exposed public. The feasibility of using readily available standard 2x2-inch sodium-iodide detectors to determine the committed effective dose to a patient following the inhalation of a radionuclide has been investigated. The 2x2-NaI(Tl) detector was modeled using the Monte Carlo simulation code, MCNP-5, and was validated via a series of experimental benchmark measurements using a polymethyl methacrylate (PMMA) slab phantom. Such validation was essential in reproducing an accurate detector response. Upon verification of the detector model, six anthropomorphic phantoms, based on the MIRD-V phantoms, were modeled with nuclides distributed to simulate inhaled contamination. The nuclides assessed included Am-241, Co-60, Cs-137, I-131, and Ir-192. Detectors were placed at four positions on the phantoms: anterior right torso, posterior right torso, anterior neck, and lateral left thigh. The detected count-rate varied with respect to detector position, and the optimal detector location was determined on the body. The triage threshold for contamination was set at an action level of 250-mSv of intake. Time dependent biokinetic modeling was employed to determine the source distribution and activity in the body as a function of post-inhalation time. The detector response was determined as a function of count-rate per becquerel of activity at initial intake. This was converted to count-rate per 250-mSv intake for triage use by first responders operating the detector to facilitate triage decisions of contamination level. A set of procedure sheets for use by first responders was compiled for each of the phantoms and nuclides investigated.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Establish limits to the exposure of the population to various ionizing radiation sources is crucial to prevent occupationally exposed individuals and the public, to their deleterious effects. In computational ambit, it is necessary that different exposure scenarios are simulated in order to obtain the dose coefficients (CCs), which relate physical dosimetric quantities - as absorbed dose, Fluency or Kerma Air - with limiting quantities - as equivalent and / or effective dose. Under certain exposure conditions, the individual's posture is not always the same, and the scenario shall be described as realistic as possible. In this work, the AM (Adult Male) and AF (Adult Female) anthropomorphic reference phantom of ICRP publication n° 110 had their postures modified from supine posture (standing) to sitting posture. The change of posture was performed through of a subroutine written in the Visual Monte Carlo code (VMC) to rotate the thigh region of the phantom and position it between the region of the leg and torso. The ScionImage software was used to reconstruct and smooth the knee and hip contours in a sitting posture phantom, and for 3D visualization of phantom was used VolView software. After this step the MCNPX radiation transport code was used for the calculation of fluence-to-dose conversion coefficients (CCs) to six irradiation geometries: AP, PA, LLAT, RLAT, ROT and ISO, recommended by ICRP. The results were compared between the phantoms in standing and sitting postures, for both sexes, in order to assess differences in scattering and absorption of radiation in different postures. The results show significant differences of up to 100% in the equivalent dose conversion coefficients of organs in the pelvic region, 79 % in organs with distribution in the whole body (such as skin, muscle, lymph nodes, bone marrow and trabecular bone) and a difference of 27% to effective dose conversion coefficients. Moreover in order to conduct a comparative study between two types of simulators, was estimated CCs equivalent and effective dose of adult male hybrid simulators, UFHADM, and female, UFHADF, in a sitting posture, and compared to the AM and AF simulators, also in the sitting posture, where it was observed significant difference in energies below 0.05 MeV. This study demonstrated the feasibility of using anthropomorphic phantoms in the sitting posture to represent more realistic postures and can be used in studies in medical and occupational dosimetry. This study demonstrated the feasibility of using anthropomorphic simulators reference in the seated position to represent more realistic positions can thus be used in studies in medical and occupational dosimetry as well as the importance of developing as realistic simulators as possible to dose estimation as faithful as possible in different irradiation scenarios. / Estabelecer limites à exposição da população a diversas fontes de radiação ionizante é de fundamental importância para prevenir indivíduos, ocupacionalmente expostos e do público, dos seus efeitos deletérios. Em âmbito computacional, é necessário que diferentes cenários de exposição sejam simulados, visando à obtenção dos coeficientes de dose (CCs), que associam grandezas dosimétricas físicas – como dose absorvida, fluência ou kerma no ar – com grandezas limitantes – como equivalente e/ou dose efetiva. Em certas condições de exposição a posição do indivíduo nem sempre é a mesma, e o cenário deve ser descrito da forma mais realística possível. Neste trabalho, os simuladores antropomórficos de referência da publicação nº 110 da ICRP, AM (Adult Male) e AF (Adult Female), tiveram suas posturas modificadas da postura supinada (em pé) para a postura sentada. A mudança de postura foi realizada por meio de uma subrotina escrita no software Visual Monte Carlo (VMC) para rotacionar a região da coxa dos simuladores e posicioná-la entre a região da perna e do tronco. O software ScionImage foi utilizado para reconstruir e suavizar os contornos no joelho e quadril dos simuladores na postura sentada, e com ferramenta auxiliar para visualização 3D dos simuladores foi utilizado o software VolView. Após essa etapa foi utilizado o código de transporte de radiação MCNPX para o cálculo dos coeficientes de conversão (CCs) de dose equivalente e efetiva por fluência de partículas, calculados para seis geometrias de irradiação AP, PA, LLAT, RLAT, ROT e ISO, recomendadas pela ICRP. Os resultados foram comparados entre os simuladores em pé e sentado, para ambos os gêneros, com o objetivo de avaliar as diferenças de espalhamento e absorção da radiação para as diferentes posturas. Os resultados dos CCs mostram diferenças significativas, de até 100 % para dose equivalente dos órgãos situados a região pélvica e 79 % em órgãos com distribuição em todo o corpo como, por exemplo, pele, músculo, nódulos linfáticos medula óssea e trabécula óssea, e uma diferença de 14 % para dose efetiva. Ademais, a fim de realizar um estudo comparativo entre dois tipos de simuladores, foi estimado os CCs de dose equivalente e efetiva dos simuladores híbridos adulto masculino, UFHADM, e feminino, UFHADF, na postura sentada, e comparado com os simuladores AM e AF, também na postura sentada, onde foi observado diferença significativa em energias abaixo de 0,05 MeV. Este estudo demonstrou a viabilidade do uso dos simuladores antropomórficos de referência na postura sentada para representar posturas mais realísticas podendo assim, ser utilizado em estudos na dosimetria médica e ocupacional, bem como a importância de desenvolver simuladores tão realista quanto possíveis para estimativa de dose tão fiéis quanto possíveis em diversos cenários de irradiação.