58 research outputs found

    Chapter Optical fibers and optical fiber sensors used in radiation monitoring

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    Communications engineering / telecommunication

    Optical fibers and optical fiber sensors used in radiation monitoring

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    peer-reviewedBy their very nature, optical fibers and, by extension, intrinsic and extrinsic optical fiberbased sensors are promising devices to be used in very different and complex environments considering their characteristics such as: capabilities to work under strong electromagnetic fields; possibility to carry multiplexed signals (time, wavelength multiplexing); small size and low mass; ability to handle multi-parameter measurements in distributed configuration; possibility to monitor sites far away from the controller; their availability to be incorporated into the monitored structure; wide bandwidth for communication applications. In the case of the optical fibers, the possibility to be incorporated into various types of sensors and actuators, free of additional hazards (i.e. fire, explosion), made them promising candidates to operate in special or adverse conditions as those required by space or terrestrial applications (spacecraft on board instrumentation, nuclear facilities, future fusion installations, medical treatment and diagnostics premises, medical equipment sterilization). Major advantages to be considered in using optical fibers/optical fiber sensors for radiation detection and monitoring refer to: real-time interrogation capabilities, possibility to design spatially resolved solutions (the capability to build array detectors), in-vivo investigations (i.e. inside the body measurements).PUBLISHEDpeer-reviewe

    The clinical translation of plastic scintillation dosimetry

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    Contemporary radiotherapy focuses on achieving the best patient outcomes by delivering highly targeted treatments that often include small fields and high dose gradients. Plastic scintillators outperform traditional dosimeters in these fields as they are close to water-equivalent. However, the translation of scintillation dosimeters into the clinic has been limited by three roadblocks. The generation of Cerenkov radiation in an optic fibre irradiated by megavoltage radiation contaminates the scintillation signal. Two Cerenkov removal methods (spectral discrimination and air core) were found to be accurate in accounting for Cerenkov radiation and their clinical robustness was improved. The light readout system is often the limiting factor for the accuracy of scintillators. PMTs outperform camera-based systems, though their implementation for array dosimetry is complex. A novel system with a multianode PMT was constructed and enabled multiple light signals from an array to be simultaneously measured. Arrays of scintillation dosimeters are difficult to create due to the complex arrangement of detectors and their optical pathways. Two innovative approaches (square waveguides and 3D printing) were used to build prototype scintillation dosimeter arrays. These arrays showed that scintillation dosimeters can measure dose distributions with high spatial and temporal resolution. Addressing these roadblocks has enabled the clinical translation of scintillation dosimeters. In small field dosimetry, an air core dosimeter was used as a reference to calculate and predict correction factors for existing dosimeters. For brachytherapy, an array of scintillators provided real-time dose measurements that improved the safety of the treatment. For rotational treatments, a cylindrical array was used to verify the dose delivered during simulated stereotactic treatments. Traditional dosimeters cannot be used in these applications and this demonstrates the potential of scintillation dosimetry

    Spectroscopic Separation of Čerenkov Radiation in High-Resolution Radiation Fiber Dosimeters

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    We have investigated Čerenkov radiation generated in phosphor-based optical fiber dosimeters irradiated with clinical electron beams. We fabricated two high-spatial resolution fiber-optic probes, with 200 and 400  μm core diameters, composed of terbium-based phosphor tips. A generalizable spectroscopic method was used to separate Čerenkov radiation from the transmitted signal by the fiber based on the assumption that the recorded signal is a linear superposition of two basis spectra: characteristic luminescence of the phosphor medium and Čerenkov radiation. We performed Monte Carlo simulations of the Čerenkov radiation generated in the fiber and found a strong dependence of the recorded Čerenkov radiation on the numerical aperture of the fiber at shallow phantom depths; however, beyond the depth of maximum dose that dependency is minimal. The simulation results agree with the experimental results for Čerenkov radiation generated in fibers. The spectroscopic technique used in this work can be used for development of high-spatial resolution fiber micro dosimeters and for optical characterization of various scintillating materials, such as phosphor nanoparticles, in ionizing radiation fields of high energy

    Recent advances in silica glass optical fiber for dosimetry applications

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    In this paper, we review the highly promising silica glass, fabricated as doped and undoped optical fiber for intended use in radiation dosimetry. The dosimetry techniques reviewed here, underpinned by intrinsic and extrinsic defects in silica glass, focus on Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Radioluminescence (RL), with occasional references to the much more established Radiation Induced Attenuation (RIA). The other focus in this review is on the various materials that have been reported earlier as dopants and modifiers used in silica glass optical fiber radiation dosimeters. This article also elaborates on recently reported optical fiber structures, namely, cylindrical fibers, photonic crystal fibers and flat fibers, as well as dimensions and shapes used for optimization of dosimeter performance. The various types of optical fiber radiation dosimeters are subsequently reviewed for various applications ranging from medical dosimetry such as in external beam radiotherapy, brachytherapy and diagnostic imaging, as well as in industrial processing and space dosimetry covering a dynamic dose range from μGy to kGy. Investigated dosimetric characteristics include reproducibility, fading, dose response, reciprocity between luminescence yield to dose-rate and energy dependence. The review is completed by a brief discussion on limitations and future developments in optical fiber radiation dosimetry

    Advances on inorganic scintillator-based optic fiber dosimeters

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    This article presents a new perspective on the development of inorganic scintillator-based fiber dosimeters (IOSFDs) for medical radiotherapy dosimetry (RTD) focusing on real-time in vivo dosimetry. The scintillator-based optical fiber dosimeters (SFD) are compact, free of electromagnetic interference, radiation-resistant, and robust. They have shown great potential for real-time in vivo RTD. Compared with organic scintillators (OSs), inorganic scintillators (IOSs) have larger X-ray absorption and higher light output. Variable IOSs with maximum emission peaks in the red part of the spectrum offer convenient stem effect removal. This article outlines the main advantages and disadvantages of utilizing IOSs for SFD fabrication. IOSFDs with different configurations are presented, and their use for dosimetry in X-ray RT, brachytherapy (BT), proton therapy (PT), and boron neutron capture therapy (BNCT) is reviewed. Challenges including the percentage depth dose (PDD) deviation from the standard ion chamber (IC) measurement, the angular dependence, and the Cherenkov effect are discussed in detail; methods to overcome these problems are also presented. Introductio

    Characterization of Yb-doped silica optical fiber as real-time dosimeter

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    The near-infrared radioluminescence and dosimetric properties of Yb-doped silica optical fibers, coupled with an optical detector prototype based on an avalanche photo-diode, were studied by irradiating the fibers with clinical beams generated by a Varian Trilogy accelerator. The performances of the system in standard and small field sizes have been also investigated comparing the output factor, percent depth dose and off axis ratio measurements of the prototypal dosimetric system with other commercial sensors. The results demonstrated that the drawback due to the stem effect in Yb-doped silica optical fibers can be managed in a simple but effective way by optical filtering. These features, together with the accuracy and precision achieved by Ybdoped fibers in relative dose assessments make the device promising for in-vivo dosimetry studies in radiation therapy

    Estudos para o sistema de rastreamento da experiência NEXT e desenvolvimento de dispositivos médicos usando SiPMs

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    Doutoramento em FísicaOs recentes desenvolvimentos na área dos fotodetectores de estado sólido, nomeadamente os fotomulplicadores de silício (SiPM), permitiram a proliferação desta tecnologia num vasto número de aplicações em áreas distintas. Estes fotosensores robustos, versáteis e com um preço competitivo, tornaram-se uma das mais promissoras alternativas aos tubos fotomultiplicadores para deteção de baixo nível de luz, especialmente para aplicações onde é necessário um grande número de fotodetectores. Estes fotosensores multi-pixel, são capazes de deteção de fotão único, permitindo obter ao mesmo tempo informação sobre fotão de interação e energia. Os estudos realizados no âmbito deste programa doutoral e reportados neste documento dividem-se em três aplicações principais: colaboração no desenvolvimento do sistema de rastreamento (tracking system) da experiência NEXT na área da física de neutrinos e Neutrinoless Double Beta Decay (0⌫""), que comporta ⇠7.000 SIPMs para identificação da assinatura 0⌫"", um dosímetro para braquiterapia de próstata e um sistema PET didático - easyPET. Foram realizados vários estudos para caracterização da nova geração de SiPMS. Como verificado, estes dispositivos apresentam características melhoradas tais como uma maior eficiência quântica e menor crosstalk, afterpulsing e sensibilidade térmica. Esta nova geração de SiPMs adequa-se aos requisitos para aplicação no tracking system no NEXT. No entanto, uma maior eficiência quântica no ultravioleta de vazio (VUV) é desejável. Foi avaliada a aplicação de SiPMs em sensores de radiação para dosimetria médica. Foi desenvolvido um dosímetro com base em fibra ótica cintilante. O dispositivo foi caracterizado numa larga gama de energia e em regimes de baixa e de alta taxa de dose. O dosímetro foi avaliado em ambiente clínico recriando as condições de braquiterapia HDR, tratamento aplicado no tratamento de cancros da próstata e mama. Conforme verificado, os SiPM apresentam elevada dependência com a temperatura sendo portanto necessárias técnicas de compensação ou de estabilização. O protótipo do easyPET foi implementado com sucesso. A tecnologia foi licenciada e é esperada a sua comercialização até ao fim do ano de 2016. Dos estudos realizados nas várias aplicações, conclui-se que os SiPMs são fotodetectores muito versáteis devido à sua alta sensibilidade, elevado ganho, insensibilidade a campos magnéticos, de rápida resposta e de pequenas dimensões, abrindo a possibilidade de aplicação desta tecnologia em múltiplos campos permitindo uma infinidade de novos conceitos de detectores, tais como na física de alta energia e aplicações de imagiologia biomédica.The recent developments of solid-state photodetectors, namely Silicon Photomultipliers (SiPMs), allowed a proliferation of this technology through numerous applications. These robust and versatile photosensors with an attractive price have become one of most promising alternatives for low light level detection, especially for applications where a large number of devices is required. These multi-pixel photosensors, capable of single photon detection, allow to obtain at the same time information on photon-interaction and energy. The Ph.D studies reported in this document cover three main applications: the NEXT experiment, a Neutrinoless Double Beta Decay (0⌫"" ) experiment using ⇠7000 SiPMs in the tracking system for topological signature identification, a dosimeter for prostate brachytherapy and a simple PET system for education purposes - the easyPET. Several studies were conducted envisaging the characterization of a new generation of SiPMs. As verified, these devices present improved features such as higher quantum
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