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When a new linear accelerator is installed at a department it is of great importance that it is carefully controlled and calibrated before being put into clinical use. This is done with the acceptance test (AT). The mechanical parameters, the beam performance and the reproducibility of the dose output are tested. For each test there is a requirement which must be fulfilled for the machine to pass
210Pb dateringsstudie på 3000-4000 meters djup gjord på sediment från Marokanska och Arabiska havet för att undersöka om djuphavssediment är en stabil miljö. Tanken med examensarbetet är att undersöka konsekvenserna för dumpning av radioaktivt avfall i havet. Vilka regler gäller och vilka problem kan uppstå. Är det säkert eller ej? Vilka dumpplatser finns det och vad har man dumpat där? Ett av målThe earth surface consists of 71% of water and 29% land. 97% of that water is contained in saline seas. More than 90 per cent of the worlds living biomass can be found in the oceans. The sea has always been a possible dumpingsite for waste produced by man. Radioactive waste is the one of the most dangerous waste of all. Since the beginning of nuclear power research dumpsites around the world has b
Den här uppsatsen handlar om installationen och kalibreringen av en halvledardetektor i en underjordisk anläggning. Avsikten men att placera sin detektor långt ner under markytan är att minimera inflytandet av den kosmiska bakgrundsstrålningen. I kalibrerings förfarandet konstruerade vi en datormodel av detektorn. Med denna datormodel kan man simulera effektivitetskalibreringen av olika strålkällaThe aim of this thesis work has been to set up an ultra low-level gamma-ray spectrometry system in the underground laboratory HADES and applying the system to measurements of activation products in tantalum discs in order to determine low neutron fluxes. The main part of the work has been the efficiency calibration of the detector and the implementation of a computermodel for Monte Carlo simulatio
"The technology for planning and delivering radiotherapy has in the last decade undergone some revolutionary development and it is now possible to perform complex treatments such as stereotactic treatments and treatments using dynamic wedges, multileaf collimator and intensity modulation. The more precise limits surrounding the PTV have made it of utmost interest to be able to verify calculat
In this study we evaluate the clinical image quality of a computed radiography system for different tube voltages. Images of anthropomorphic phantoms were produced and the quality of the images was evaluated using visual grading analysis (VGA) by a group of experienced radiologists. Two different X-ray examinations were investigated: chest PA and pelvis AP. The exposure conditions were set so that
Mat som kontaminerats av radionuklider genom till exempel radioaktivt nedfall kan ge höga stråldoser till kroppen. Nuklider med långa halveringstider kan ackumuleras i kroppen och ge en hög tidsintegrerad absorberad dos. Personer med kronisk njursvikt kan erhålla höga stråldoser efter intag av radionuklider eftersom många radionuklider utsöndras via njurarna. I den här undersökningen har vi studerHigh internal radiation doses can result from food, contaminated by radionuclides from for example nuclear fallout. Nuclides with long half-lifes can accumulate in the body and give a high time-integrated absorbed dose. Persons with end-stage renal disease can receive high absorbed doses after intake of radionuclides, since many radionuclides are mainly excreted by the kidneys. In this study the d
The atmospheric nuclear bomb test “Castle Bravo”, which detonated at the Bikini Atoll in the Marshall Islands in 1954, led to the contamination of some populated atolls. Sediment samples from one such, the Rongelap Atoll, have been examined for plutonium (239, 240, 241, 242Pu) and americium (241Am) at Lawrence Livermore National Laboratory in Californina. Plutonium was measured with Accelerator Ma
The evaluation of clinical radiographs with the European Image Criteria method has in previous work proven to be an easy and straightforward method. The main drawback with this method is the large inter-observer variation. It has been proposed that the reason for this is that the observers get “distracted” by the surrounding structures in the image and that a sort of “first impression” of the imag
Phosphorus magnetic resonance spectroscopy (31P NMR) is a non-invasive technique for determining concentrations of intracellular metabolites linked to energy metabolism of human tissues. Inorganic phosphate (Pi) and adenosine triphosphate (ATP) are found in most tis-sues, while tissue specific metabolites such as creatine phosphate (PCr) and metabolites linked to lipid metabolism can be observed i
Motivationen med studien var den alldeles för höga stråldosen som används vid CTundersökningar. I de allra flesta fallen anpassas man inte rörströmmen efter patientens storlek och därmed får smalare patienter en onödigt hög stråldos. Målet var att reducera stråldosen till patienter som undersöks med datortomografi utan att minska på bildkvalité, genom att anpassa rörströmmen efter patientens stoIn this study we have investigated the possibilities of dose reduction in CT at a constant level of image quality by adjustment of the tube current to the phantom size. The motivation with the study is the high radiation doses to the patients and the increasing frequency of CT examinations and the variety of examinations in CT, and that the same tube current is used for different patient sizes. Ac
Funktionell magnetresonanstomografi (fMRI) är en teknik som gör det möjligt att kartlägga aktivering inom olika delar av hjärnan. Genom att samla in bilddata då patienten är i vila, och sedan jämföra dessa med data insamlade medan patienten är aktiv (t.ex. utför fingerrörelser), kan en bild skapas som visar var i hjärnan aktivering har skett. Dessa bilder kan t.ex. användas för att bedöma om det äFunctional MRI (fMRI) is a technique for determining which parts of the brain are activated when a subject experiences some type of physical sensation or performs an activity. This technique has during the past several years become a very useful tool for understanding functions of the nervous system, and the development of clinical applications is rapidly progressing. However, fMRI is not straight
Effects of flow are a fundamental part of magnetic resonance imaging (MRI). Since almost every part of the body contains some kind of flow, the effects are seen in generally all MR images. The presence of flow in an image slice may be a vast source of artefacts but the effects of flow can also be used for diagnostic purposes, for example in magnetic resonance angiography (MRA). In MRA, flow effect
Diffusionsviktad magnetiskresonanstomografi (MRT) är en metod där vi med hjälp av magnetfält kan märka in vattenmolekyler och följa de slumpmässiga rörelser som alla molekyler uppvisar. Den slumpmässiga rörelsen uppstår p.g.a. termisk energi (värmeenergi) och varierar med temperaturen och ämnet som omger molekylerna. Tensoranalys är ett matematiskt verktyg för att skapa modeller för hur den omgivaDiffusion weighted magnetic resonance imaging (MRI) is a modality that offers the possibility to measure molecular motion such as water self-diffusion which is in the order of 10-9 m2/s. The basic formalism has been known since the middle of the 20:th century, it is however, only during the last decade that it has been used for imaging. Through tensor analysis of diffusion weighted images, acquire
Up to recently mobile gamma spectrometry has mostly been performed with NaI(Tl)-based detector systems. However lately the interest of using HPGe(High Purity Germanium)-based systems have increased and one has realised that the excellent energy resolution of HPGe-detectors, in combination with the possibility to manufacture larger crystals than before, is an advantage not only when performing in s
A patient positioning system for Boron Neutron Capture Therapy (BNCT) for treatment of brain tumours was designed, and its accuracy was evaluated. The system will be used at the BNCT facility under construction at Studsvik, Sweden. Recent studies have shown that the accuracy in the patient positioning procedure in BNCT is of more significance than generally perceived in the past. Therefore one obj
Idag behandlas många former av cancer med joniserande strålning från linjäracceleratorer. Målet med behandlingen är att sterilisera cancercellerna med så liten påverkan som möjligt på den friska vävnaden. För att uppnå detta är det viktigt att ha en så bra bestämning som möjligt av den absorberade dosen till tumör- och normalvävnad. För detta ändamål används idag tredimensionella dosplaneringssystA Monte Carlo generated linear accelerator is implemented into a pencil beam based treatment planning system (TPS) to study the possibility to verify the TPS with a Monte Carlo method. The implemented accelerator is then used to study two inhomogeneous lung geometries; lungslab and mediastinium. Advantages of a Monte Carlo method over conventional measurements are that accelerator output variation
Diffusion is a molecular phenomenon and can be described as the process by which matter is transported from one part of a system to another as a result of random molecular motion. The diffusion coefficient is then a quantity that describes the mobility of the molecules in a media. In recent years, methods have been developed to image the diffusion of water in human tissue using magnetic resonance
"At searching for lost point sources, it is important to use an optimal search strategy and an optimal methodology for spectrum data analysis. The purpose of this work is to evaluate a simple on-line method for locating lost point sources in the environment with carborne gamma spectrometry and study different strategies for detector geometries and speed of the car. The scope of this thesis
The characterization of the incident photon beam is usually divided into its dependence on collimator setting (head-scatter factor) and off-axis position (primary off-axis ratio). These parameters are normally measured "in air" with a build-up cap, thick enough to generate full dose build-up at the depth of dose maximum. In order to prevent any influence from contaminating electrons, it
In this report the characteristics of the electron applicator system for an Elekta SLi Plus linear accelerator have been studied. The investigation will serve as a basis for a new applicator design that will give less radiation leakage. The present applicator system does not fully comply with the recommendations of the International Electrotechnical Commission (IEC) Standards recording radiation l
