1,720,984 research outputs found
Development of a 3D dosimetric method by gel and optical readout for the implementation of end-to-end quality assurance in stereotactic radiotherapy
No full textLes techniques modernes de radiothérapie externe, telles que la radiothérapie stéréotaxique qui utilise des petits faisceaux d'irradiation, permettent aujourd'hui de délivrer précisément de fortes doses à la tumeur tout en épargnant les tissus sains adjacents. Cette amélioration s'accompagne cependant d'une complexification des plans de traitement délivrés. Il est alors nécessaire de sécuriser les traitements par la mise en place de contrôles qualité adaptés à ces nouvelles techniques. Parmi ceux-ci, les contrôles qualité end-to-end permettent de tester l'ensemble de la chaîne de traitement rencontrée par les patients à l'hôpital. Les gels dosimétriques, encore à l'état de recherche, pourraient permettre une meilleure mise en place de ce type de contrôles car ils sont actuellement les seuls dosimètres capables de mesurer des distributions de dose en 3D avec une haute résolution spatiale. Le gel Fricke-Xylenol orange-Gelatin (FXG) associé à une lecture par tomographie optique a déjà été utilisé dans la littérature pour réaliser des contrôles qualité end-to-end, cependant sa gamme de dose d'utilisation était limitée à 4 Gy et ne permettait pas son utilisation pour des applications stéréotaxiques. Dans cette étude, la composition du gel FXG a été optimisée et une méthode de double lecture optique a été développée afin d'envisager l'utilisation de cette méthode dosimétrique sur une gamme de dose représentative des traitements stéréotaxiques ([0,25 ; 10] Gy). Cette méthode a été caractérisée et validée dans des petits champs d'irradiation. Plusieurs contrôles qualité end-to-end ont ensuite été mis en place en milieu clinique pour le traitement de tumeurs intracrâniennes par stéréotaxie sur les accélérateurs Novalis TrueBeam STx (Varian) et CyberKnife (Accuray). Les distributions de dose mesurées par gel et celles planifiées ont été comparées en utilisant différents outils d'analyse tels que le gamma-index et la superposition de courbes isodoses, de profils de dose et d'histogrammes dose-volume. Des mesures ponctuelles et planaires avec d'autres dosimètres ont aussi été effectuées pour compléter cette comparaison. Les résultats obtenus ont montré que la méthode de contrôle qualité 3D end-to-end par gel FXG et double lecture optique est précise, adaptée à la radiothérapie stéréotaxique et apporte des informations supplémentaires aux contrôles qualité actuellement effectués en routine clinique avec des méthodes dosimétriques plus conventionnelles.Modern external radiotherapy techniques, such as stereotactic radiotherapy which uses small radiation beams, enable to deliver precisely high doses to the tumor, while sparing adjacent healthy tissues. However, this improvement goes with increasing complexity of the treatment plans delivered and it is, therefore, necessary to ensure the safety of these treatments through adapted quality assurance. End-to-end quality assurance is a unique tool to test the whole treatment chain encountered by patients in hospitals. Dosimetric gels, which are still in the research stage, could enable a better implementation of this type of quality assurance as they are currently the only dosimeters able of measuring 3D dose distributions with high spatial resolution. Fricke-Xylenol orange-Gelatin (FXG) gel read by optical computed tomography has already been used in the literature to perform end-to-end quality assurance, however on a dose range restricted to 4 Gy, which is not adapted to stereotactic treatments. In this study, the composition of the FXG gel has been optimized and a dual-wavelength reading method has been developed in order to span an absorbed dose range representative of stereotactic treatments (0.25 - 10 Gy). This method has been characterized and validated in small irradiation fields. Then, end-to-end quality assurance tests have been implemented in a clinical setting for the treatment of intracranial tumors by stereotactic radiotherapy on the Novalis TrueBeam STx (Varian) and the CyberKnife (Accuray) accelerators. The planned and measured dose distributions have been compared using different analysis tools, such as gamma-index and superposition of isodose curves, dose profiles and dose-volume histograms. Point and planar measurements with other dosimeters have also been performed to extend this comparison. The results obtained have shown that the 3D end-to-end quality assurance method using FXG gel and dual-wavelength optical readout is accurate, appropriated for stereotactic radiotherapy and provides additional information to the quality assurance currently performed in clinical routine with more conventional dosimetric methods
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Personalized patient dose estimation for on board KV-CBCT imaging systems and reflections on the clinical management
No full textLes 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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