Source: Dissertation Abstracts International, Volume: 40-06, Section: B, page: 2731. / Thesis (Ph.D.)--The Florida State University, 1979.

Single crystals of l-asparagine monohydrate and partially deuterated l-asparagine were x-irradiated at 4.2K, 77K, and room temperature by a 3Mev Van de Graaff electron accelerator. Several free radical species were produced by the x-irradiation and were studied by X-band ESR and ENDOR from 4.2K to 300K. X-irradiation at 77K produced two anion radicals, radicals I and III, with the unpaired spin at the carboxyl, and amide end of the molecule, respectively. Production of III must be less probable than I, since the ESR spectra of III appear to be less intense. X-irradiation at 77K also produced one cation radical (II), the decarboxylation radical. The ESR spectra of radical I are the most intense. Hyperfine tensors were determined for hydrogen ENDOR lines belonging to radicals I, II, and III. In addition, ENDOR lines for one nitrogen and two deuterium lines were observed. Tensors were determined for the nitrogen and one of the deuterium nuclei. These nitrogen and deuterium couplings were needed to explain the ESR spectra of radical II. There was probably another radical present at 77K, but there was not enough information to identify it. Radicals I, II, and III were also produced by x-irradiation at 4.2K. New unidentified ENDOR lines appeared after warming to 128K. Radicals I, II, and III were still observed at this temperature, but the ESR spectra have changed somewhat. After warming to 150K, radical I's ESR spectrum was not observed. Radical VI, the deamination radical, appears to begin to grow in at this temperature. Upon warming to 210K, radical II began decay by hydrogen abstraction to form radical IV which was identified in an earlier room temperature study. Three new ENDOR lines, though not completely followed through all orientations, combine correctly to predict the ESR spectral width along the c axis. Radical VI's ESR spectra became stronger after / warming to room temperature. For x-irradiation (of deuterated samples) at 300K, radical VI's spectra was much weaker than radical IV's, but for x-irradiation at 77K followed by warming to 300K radical VI's spectra was almost as intense as radical IV's spectra. / Source: Dissertation Abstracts International, Volume: 46-09, Section: B, page: 3105. / Thesis (Ph.D.)--The Florida State University, 1985.

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<p> The Spin Asymmetries of the Nucleon Experiment (SANE) measured the proton spin structure function <i>g</i>₂ in a range of Bjorken <i>x,</i> 0.3 &lt; <i>x</i> &lt; 0.8, where extraction of the twist-3 matrix element <i>d</i>₂<i>^p</i> (an integral of <i>g</i>₂ weighted by <i>x</i>²) is most sensitive. The data was taken from <i>Q</i>² equal to 2.5 <i>GeV</i>² up to 6.5 GeV². In this polarized electron scattering off a polarized hydrogen target experiment, two double spin asymmetries, <i> A</i>&par; and <i>A</i>_&perp; were measured using the BETA (Big Electron Telescope Array) Detector. BETA consisted of a scintillator hodoscope, gas &Ccaron;erenkov counter, lucite hodoscope and a large lead glass electromagnetic calorimeter. With a unique open geometry, a threshold gas &Ccaron;erenkov detector allowed BETA to cleanly identify electrons for this inclusive experiment. A measurement of <i>d</i>₂<i>^p</i> is compared to lattice QCD calculations.</p>

Current dose photon calculation algorithms have shortcomings in calculating dose distributions accurately in complex, heterogeneous phantoms. In this work, using existing Monte Carlo (MC) algorithms, we implemented and validated a comprehensive MC treatment planning system (MCTPS). We compared MCTPS with the corrected pencil beam algorithm used in the commercial TPS, CadPlan (V2.7.3). The accuracy of dose distributions calculated by MCTPS was studied for six lung cancer patients in two modes: without correction for inhomogeneity (the clinically used method) and with the equivalent tissue air ratio (EgTAR) inhomogeneity correction switched on. Without the use of inhomogeneity corrections, absorbed dose estimated by CadPlan is in error by more than 10% in the planning target volume (PTV). With the EgTAR correction, good agreement was observed for the dose to the PTV, however, in regions close to an interface, where a significant density gradient occurs, the error is up to 10%. Dose errors in other organs were studied using differential dose volume histograms.

Monte Carlo (MC) dose calculations cannot accurately assess the dose delivered to the patient during radiotherapy unless the patient anatomy is well known. This thesis focuses on the conversion of patient computed tomography (CT) images into MC geometry files. Metal streaking artifacts and their effect on MC dose calculations are first studied. A correction algorithm is applied to artifact-corrupted images and dose errors due to density and tissue mis-assignment are quantified in a phantom and a patient study. The correction algorithm and MC dose calculations for various treatment beams are also investigated using phantoms with real hip prostheses. As a result of this study, we suggest that a metal artifact correction algorithm should be a part of any MC treatment planning. By means of MC simulations, scatter is proven to be a major cause of metal artifacts. The use of dual-energy CT (DECT) for a novel tissue segmentation scheme is thoroughly investigated. First, MC simulations are used to determine the optimal beam filtration for an accurate DECT material extraction. DECT is then tested on a CT scanner with a phantom and a good agreement in the extraction of two material properties, the relative electron density rho_e and the effective atomic number Z is found. Compared to the conventional tissue segmentation based on rho_e-differences, the novel tissue segmentation scheme uses differences in both rho_e and Z. The phantom study demonstrates that the novel method based on rho_e and Z information works well and makes MC dose calculations more accurate. This thesis demonstrates that DECT suppresses streaking artifacts from brachytherapy seeds. Brachytherapy MC dose / Les calculs de dose Monte Carlo (MC) ne peuvent précisément déterminer la dose délivrée au patient, à moins de bien connaître son anatomie. Cette thèse se concentre sur la conversion des images tomographiques du patient en fichier de géométrie Monte Carlo. Les artefacts métalliques et leur effet sur les calculs de dose MC sont étudiés. Un algorithme de correction est appliqué sur les images avec artefacts et les erreurs de dose dues au mauvais assignement des densités et tissus sont quantifiées dans un fantôme et une étude de patient. L'algorithme de correction est aussi testé sur des fantômes avec de réelles prothèses de hanches et l'effet de correction sur les calculs de dose MC est étudié. En tant que résultat de cette étude, nous suggérons qu'un algorithme de correction des artefacts métalliques soit intégré à tout plan de traitement MC. Par le biais de simulations MC, le diffusé est prouvé être une cause majeure des artefacts métalliques. L'utilisation d'un scanner double énergie pour une méthode novatrice de segmentation de tissu est minutieusement étudiée. Tout d'abord, les simulations MC sont utilisées pour déterminer la filtration optimale de faisceau pour une extraction précise du matériau en scanner double énergie. La méthode à double énergie est ensuite testée sur un scanner avec un fantôme et un bon accord dans l'extraction des propriétés des deux matériaux, la densité électronique relative rho_e et le nombre effectif atomique Z est trouvé. Comparé à la segmentation conventionnelle des tissus réalisée sur la base des différents rho_e, la méthode novatrice de segmentation de tissu utilise les diff

In this thesis, a two-part investigation was conducted to determine methods of reducing the inaccuracy in the treatment of solid tumors in the lung. In the first part, a visual feedback system was investigated for use during respiratory gating procedures, both during simulation and treatment. The visual feedback system was installed in the clinic and was used by three patients during radiotherapy and by approximately 15 patients during simulation. The use of the visual feedback was found to increase the regularity of the patients’ breathing patterns and improved the ability of the gating technique to compensate for internal tumor motion. The second part consisted of a comparison of the dose distribution algorithms of the Eclipse treatment planning system with dose calculations performed using Monte Carlo methods based on the EGSnrc and DOSXYZnrc user codes for BEAMnrc. Four patients with lung tumors, whose treatment plans called for small, 18 MV photon fields, were recalculated using both systems. Results showed that the algorithms used by the TPS consistently overestimated the dose in the lung, due to the lack of lateral electron equilibrium in the lung tissue. / Dans ce mémoire, une enquête en deux parties à été entreprise pour analyser des méthodes permettant la réduction d’erreurs dans le traitement des cancers pulmonaires. Dans la première partie de l’enquête, nous analysons un système de « feedback » visuel utilisé avec les procédures de « gating » en simulation et en radiothérapie. Ce système a été installé dans la clinique et utilisé par trois patients pendant la radiothérapie et une quinzaine de patients pendant des simulations CTs. Il a ainsi été observé que l’utilisation du « feedback » permettait de régulariser la respiration des patients et ainsi d’optimiser l’utilisation des techniques de « gating » afin de réduire l’effet des mouvements interne des tumeurs durant la thérapie et les simulations. La deuxième partie de l’enquête consistait en une étude retrospective qui avait pour but de permettre la comparaison de plusieurs algorithmes de calcul de dose. Les résultats obtenus à l’aide des algorithmes du système de planification de traitements Eclipse ont été comparés à ceux qui ont été calculés en utilisant les codes Monte Carlos EGSnrc et DOSXYZnrc. Les données de quatre patients souffrant du cancer du poumon qui avaient étés traités avec des faisceaux de photons 18 MV ont ainsi été recalculées. Les résultats obtenus ont démontré que les algorithmes d’Eclipse surestimaient systématiquement les doses à cause de la faible densité des tissus pulmonaires et du manque d’équilibre électronique dû au dimensions des faisceaux.

In a radiation therapy department, several periodic (daily, monthly, quarterly, yearly, etc.) and on-request quality control tests are performed as part of the quality assurance program. The lack of a commercial solution to unify all these tests in one single system was the motivation for this project. The goal of this thesis work was to develop a web-based quality assurance software tool for the radiation oncology division of the Jewish General Hospital that would be easily expendable and manageable. The tool that was created allows easy access to the tests through a simple web interface yet allowing advanced management of user rights, processing of complex numerical data, warning users through email alerts and reports, scheduling tests, keeping trends of the test results and providing safe storage for the collected data. Our system is based on Drupal, an open source web content management system. Several customizations were done to the basic Drupal system to adapt it to our needs: several scripts and specialized modules were used to enter and analyse collected data (text and images) as well as exchange data with the radiotherapy electronic medical record database. In this thesis work we have selected and implemented in our system a limited collection of quality control tests (9) that are representative of all types of tests that are performed in a radiotherapy clinic, as a full implementation would be beyond the time frame of this project. They are the bases for a future complete implementation and can be used as a model for other similar tests. The implemented tests are now being introduced in the clinic simplifying data entry, access, and analysis. / Dans un département de radiothérapie plusieurs tests de contrôle de qualité sont exécutés de façon périodique (journalière, mensuelle, trimestrielle, annuelle, etc.) où sur demande dans le cadre du programme d'assurance qualité. L'absence d'une solution commerciale pour unifier tous ces tests dans un seul système informatique est la motivation de ce projet. L'objectif de ce travail de thèse était de développer un outil logiciel web d'assurance qualité pour la division de radio-oncologie de l'Hôpital général juif qui serait facilement extensible et facile à gérer. L'outil qui a été créé permet un accès facile à des tests via une interface web simple tout en permettant une gestion avancée des droits des utilisateurs, du traitement des données numériques complexes, permet l'envoie d'alertes e-mail et de rapports, la planification temporelle des tests, l'analyse des tendances des résultats et le stockage des données recueillies.Notre système est basé sur un logiciel libre de gestion de contenu, Drupal. Plusieurs adaptations ont été apportées au système Drupal de base pour l'adapter à nos besoins: plusieurs scripts et modules spécialisés ont été programmés et utilisés pour saisir et analyser les données recueillies (texte et images) ainsi que l'échange de données avec la base de données de dossiers médicaux électroniques de radiothérapie. Dans ce travail de thèse, nous avons sélectionné et implémenté dans notre système une collection limitée de tests de contrôle de qualité (9) qui sont représentatifs de tous les types de tests qui sont effectués dans une clinique de radiothérapie puisque la mise en œuvre complète de tous les tests est au-delà du délai de cette projet. Les tests implémentés peuvent facilement être utilisés comme modèles pour les autres tests. Les tests présentement implémentés sont en cours d'introduction dans la clinique et simplifie la saisie, l'accès et l'analyse aux données.

Measurements of modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) for metal/film portal detectors are reported for the Cobalt-60 and 10 MV spectra. The detectors consist of a double-emulsion portal film secured between plates of aluminum, copper, brass or lead with thicknesses from 0 to 4.81 mm. The study of MTF, NPS, and DQE shows that both photons and secondary electrons produced within the front-plate and backscattered electrons from the back-plate affect metal/film portal imaging. Study of DQE indicates that the best portal detectors are those without back-plates, and with high density front-plates with thicknesses less than the maximum electron range. / This MTF data was modeled with the logit analysis. It is shown that the parameters resulting from the logit analysis depend on the mass thickness and the atomic number of the metal plates. / Metal/amorphous selenium (a-Se) electrostatic-based detectors have been developed for portal imaging. The detectors consist of a-Se photoconductive layers of varied thicknesses deposited on plates of varying thicknesses of aluminum, copper, and stainless steel. The metal-plates of the detectors face the incident 6 MV and Co-60 photon spectra during imaging. The sensitivity of the a-Se detectors to dose, electric field across the a-Se layer, plate type, and a-Se thickness is studied. A model showing a cubic relationship between the a-Se latent surface voltage and dose is derived and experimentally verified. A contrast-detail phantom is used to study the image quality and contrast-resolution characteristics of the metal/a-Se detectors. The metal/a-Se detectors produce better quality contrast-detailed images at a considerably lower dose than that offered by the other commercial available portal systems, mainly due to the low inherent noise of the novel detectors. / A semi-automatic technique for the direct set-up alignment of radiosurgical circular fields from an isocentric linac to treatment room laser cross-hairs is described. Because film or a-Se is each sensitive to laser and ionizing radiation, they are used to acquire images of the positioning lasers superimposed directly onto the radiosurgical circular fields. An algorithm extracts the coordinates of the center of the collimator image and of the intersection of the laser cross-hair image and subsequently determines the deviation, to within a precision of &sim;0.04 mm. The technique is also used to perform quality assurance on a Clinac-18 linac and shows a (0.53 +/- 0.05) mm wobble from the nominal isocenter of the linac.

Recent studies in medical physics have focused on the application of low atomic number (Z) targets for their effect on contrast in megavoltage portal imaging and cone-beam computed tomography (CBCT). This work seeks to compliment those studies by investigating the effects of varying different target parameters including atomic number, thickness and incident electron energy on spatial resolution in megavoltage planar imaging and CBCT. Target materials of beryllium (Be, Z = 4), aluminum (Al, Z = 13) and tungsten (W, Z = 74) were investigated over a variety thicknesses between 10% and 100% of the continuous slowing down approximation range. Incident electron kinetic energies of 4.5 MeV and 7.0 MeV were used along with custom targets installed into the carousel of a Varian 2100EX linear accelerator (Varian Medical, Inc.) to produce the experimental beams of interest. Monte Carlo simulated results were compared to measured data and it was shown that thinner targets are generally superior to thicker targets and that higher incident electron energies produce better results. Due to a dependence of the MTF of the detector system on photon energy, it was shown that low Z targets produced superior spatial resolution. Simulations also showed a 14.5% and 21.5% increase in spatial frequency in which the modulation transfer function dropped to half of its maximum (f_50) for the 7.0 MeV and 4.5 MeV targets, respectively, when moved from the carousel to the location of the clinical target. The f_50 values of the custom targets were compared to the clinical 6 MV beam and were found to be between 10.4% lower and 15.5% higher than the 6 MV value. Low-Z CBCT sets were acquired using the CATphan phantom and compared to the clinical 6 MV beam and kilovoltage CBCT sets. Using the low-Z targets it was possible to resolve the 0.5 lp/mm, compared to 0.4 lp/mm and 1.0 lp/mm for the clinical 6 MV and kilovoltage sets respectively. / Récemment, plusieurs recherches se tournent vers l'emploi de cibles à petits numéros atomic (Z), et mesurent leurs effets sur le contraste de l'imagerie de portail de megavoltage et de tomographie calculée à faisceau cônique (CBCT). À l'avenant, cet ouvrage étudie les effets de la variation de différents paramètres de la cible, tel le numéro atomic, l'épaisseur, et l'énergie de l'electron incident, sur la résolution spaciale des deux techniques d'imageries mentionnées. Des cibles de béryllium (Be, Z = 4), d'aluminium (Al, Z = 13), et de tungstène (W, Z = 74) sont étudiées sous une gamme d'épaisseures entre 10 % et 100 % de l'amplitude de l'approximation de ralentissement continue (CSDA). Des électrons incidents avec des énergies cinétiques de 4.5 MeV et 7.0 MeV sont utilisés avec une cible personnalisée, installée sur le carrousel d'un accélérateur linéaire Varian 2100EX (Varian Medical, Inc.), afin de produire les faisceaux désirés. Des résultats Monte Carlo simulés sont comparés aux résultats mesurés. Les cibles minces sont géréralement supérieures aux cibles plus épaisses, et les électrons incidents à plus haute énergies produisent de meilleurs résultats. Les cibles à petits Z produisent des résolutions supérieures en raison d'une dépendence du MTF du système de detection sur l'énergie des photons. Les simulations montrent une hausse de 14.5 % et de 21.5 % du f_50 pour les cibles de 7.0 MeV et 4.5 MeV, respectivement, quand celles-ci sont déplacées du carrousel à l'emplacement clinique de la cible. Les f_50 des cibles personnalisées sont entre 10.4 % sous et 15.5 % au-dessus du f_50 du faisceau clinique à 6 MV. Les données pour le CBCT à petit Z sont obtenues avec un fantôme CATphan et comparées aux données du faisceau clinique à 6 MV et du CBCT de kilovoltage. Avec une cible à petit Z, une résolution de 0.5 lp/mm est atteinte, comparé à