High spatial resolution inorganic scintillator detector for high energy X-ray beam at small field irradiation

International audiencePurpose: Small fielddosimetry for radiotherapy is one of the major challenges due to the size of most dosimeters,e.g. sufficient spatial resolution, accurate dose distribution and energy dependency of the detector. In this context, the purpose of this research is to develop a small size scintillating detector targeting small field dosimetry and compare its performance with other commercial detectors. Method: An inorganic scintillator detector (ISD) of about 200 μm outer diameter was developed and tested through different small fields dosimetric characterization under high energy photons (6 MV and 15 MV) delivered by an Elekta Linear Accelerator (LINAC). PDD and beam profile measurements were compared using dosimeters from PTW namely, microdiamond and PinPoint 3D detector. A background fiber method has been considered to quantifyand eliminate the minimal Cerenkov effect from the total optical signal magnitude. Measurements were performed inside a water phantom under IAEA Technical reports series recommendations (IAEA TRS 381 and TRS 483). Results:Small fields ranging from 3 x 3 cm2, down to 0.5 x 0.5 cm2 were sequentiallymeasured using the ISD and commercial dosimeters, and a good agreement was obtained among all measurements. The result also shows that, scintillating detector has good repeatabilityand reproducibility of the output signal with maximum deviation of 0.26% and 0.5% respectively. The Full Width Half Maximum (FWHM) was measured 0.55 cm for the smallest available square size field of 0.5 x 0.5 cm2, where the discrepancy of 0.05 cm is dueto the scattering effects inside the water and convolution effect between field and detector geometries. Percentage Depth Dose (PDD) factor dependence variation with water depth exhibits nearly the same behavior for all tested detectors. The ISD allows to perform dose measurements at a very high accuracy from low (50 cGy/min) to high dose rates (800 cGy/min) and found to be independent of dose rate variation. The detection system also showed an excellent linearity with dose; hence calibration was easily achieved. Conclusions: The developed detector can be used to accurately measure the delivered dose at small field during the treatment of small volume tumors. The author’s measurement shows that despite using a non-water equivalent detector, the detector can be a powerful candidate for beam characterization and quality assurance in e.g., radiosurgery, Intensity Modulated Radiotherapy (IMRT), and brachytherapy. Our detector can provide real-time dose measurement and good spatial resolution with immediate readout, simplicity, flexibility, and robustness

Nouvelle génération de sondes à RX pour la radiothérapie et l'instrumentation pour la physique des surfaces

Le traitement moderne par radiothérapie est motivé par la demande constante d'un détecteur dosimétrique approprié. Plus récemment, seuls quelques détecteurs se sont montrés prometteurs dans ce sens, mais ils présentent plusieurs obstacles lors de leur mise en œuvre, tant pour les applications à forte dose de rayonnement que pour celles à faible dose. Les dosimètres à rayons X développés industriellement sont encore limités par l'exigence de taille importante, l'effet de moyennage de volume, le manque de sensibilité et le faible rapport signal/bruit, etc. Dans ce contexte, ce travail de thèse est consacré à la conception et à la fabrication d'un nouveau détecteur de rayons X extrêmement compact, en temps réel et très sensible. Le principe du dispositif est basé sur des clusters scintillantes qui sont greffées à l'extrémité d'une petite fibre centrale. Sous irradiation aux rayons X, les clusters émettent de la lumière visible qui est collectée par un compteur de photons à travers la fibre optique. Le détecteur développé a été testé pour la caractérisation de petits champs (inférieurs à 0,5 x 0,5 cm²) en radiothérapie et également en brachythérapie. Dans les deux cas, le détecteur présente d'excellentes performances.En outre, un détecteur similaire à tête nanométrique a été mis en œuvre pour la physique des surfaces au moyen d'une nouvelle technique à double sonde (STM/Fibre). Ainsi, les résultats de cette recherche explorent la dosimétrie des rayonnements miniaturisés avec l'amélioration des traitements des tumeurs de stade précoce. En outre, dans le domaine de l'imagerie des surfaces, une nouvelle technique de caractérisation des matériaux sera mise au point.The modern radiation therapy treatment is driven by the everlasting demand of a suitable dosimetric detector. Most recently, only a few detectors have shown promise in this direction, but exhibiting several barriers while implementing both in high and low radiation dose applications. The industrially developed X-ray dosimeters/detectors are still limited by the significant size requirement, volume averaging effect, lack of sensitivity, and low signal-to-noise ratio, etc. In this context, this thesis work is devoted to the design and fabrication of a novel extremely compact, small-scale, real-time, dynamic, and highly sensitive X-ray detector. The device principle is based on scintillating clusters that are grafted at the extremity of a small core fiber. Under X-ray irradiation, clusters emit visible light that is collected by a photon counter through the optical fiber. The developed detector was tested for small (lower than 0.5 x 0.5 cm²) field characterization in radiotherapy. It also allows characterizing radiation dosimetry in brachytherapy. In both cases, the detector demonstrates excellent performances when compared to the existing dosimeters and MC simulation.In addition, a similar detector with nano-metric head was implemented for the application in surface physics by means of a novel dual-probe (STM/Fiber) technique. Thus, the outcomes of this research explore miniaturized radiation dosimetry and will disclose the path of enhancing early-stage tumor treatments through real-time dosimetry. Moreover, the performance of the probe in surface imaging will open the path of novel material characterization technique allowing simultaneous sample imaging

A survey of people movement analytics studies in the context of smart cities

With the advent of the newest emergency call mandates in US and Europe, with the advances in cellular-based and WiFi-based localization solutions, and with the developments of cloud computing and web-based social networks, the location information and movement-related data is becoming easier and easier to collect from the user mobile devices and from the user cloud data and it is more and more used in a variety of Location Based Services and for various network planning and management tasks. The last decade has seen significant research efforts dedicated to analyze the user location and movement data, to extract mobility patterns and features and to use the predicted patterns for a more efficient resource allocation and for better location-based services. In the context of what is called today 'the smart city', user mobility and location data are becoming key components of the smart city architecture and applications. The goal of this paper is to give a compact and comprehensive overview of the challenges andsolutions related to collecting, storing, analyzing, visualizing, using or distributing people's movement data and to summarize the purposes of such data in the context of the smart cities and the Internet of Things.Peer reviewe

Dosimetric characterization of a small-scale (Zn,Cd)S:Ag inorganic scintillating detector to be used in radiotherapy

International audienc

High resolution small‐scale inorganic scintillator detector: HDR brachytherapy application

International audiencePurpose: Brachytherapy (BT) deals with high gradient internal dose irradiation made up of a complex system where the source is placed nearby the tumor to destroy cancerous cells. A primary concern of clinical safety in BT is quality assurance to ensure the best matches between the delivered and prescribed doses targeting small volume tumors and sparing surrounding healthy tissues. Hence, the purpose of this study is to evaluate the performance of a point size inorganic scintillator detector (ISD) in terms of high dose rate brachytherapy (HDR-BT) treatment. total signal in all the irradiations. Excellent symmetrical behavior of the dose rate regarding source position was observed at different radiation planes. Finally, a comparison with TG-43 reference dataset shows that corrected measurements agreed with simulation data within 1.2% and 1.3%, and valid for the source-to-detector distance greater than 0.25 cm. Conclusion: The proposed ISD in this study anticipated that the system could be promoted to validate with further clinical investigations. It allows an appropriate dose verification with dwelltime estimation during source tracking and suitable dose measurement with a high spatial resolution both nearby (high dose gradient) and far (low dose gradient) from the source position