Batteryless NFC dosimeter tag for ionizing radiation based on commercial MOSFET

This paper reports the development, evaluation and validation of DosiTag, a dosimetric platform based on Near Field Communication (NFC) technology. The designed system comprises two main parts: a passive NFC sensing tag as the dosimeter unit, which includes a commercial P-channel MOSFET transistor as radiation sensor; and an NFC-enabled smartphone running a custom-developed application as the reader unit. Additionally, a cloud service based on the messaging protocol Message Queue Telemetry Transport (MQTT) has been implemented using a broker/client architecture to allow the storage and classification of the patient’s data. The dosimeter tag was designed using commercial low-power integrated circuits (ICs) and it can operate without any external power supply or battery, being supplied by the smartphone through the radio frequency (RF) energy harvested from the NFC link. The radiation dose is measured through the increase of the DMOS transistor source voltage using the smartphone as the reader unit. Two tag prototypes have been characterized with a 6 MV photon beam and radiation doses up to 57 Gy and 42 Gy, respectively. The achieved average sensitivity is (4.37 ± 0.04) mV/ Gy with a resolution of 2 cGy, which goes beyond the state-of-the-art of previous NFC dosimeters and places DosiTag as a low-cost promising electronic platform for dose control in radiotherapy treatments.Junta de Andalucía (Spain), projects numbers PI-0505–2017 FEDER/Junta de Andalucía- Consejería de Economía y Conocimiento Project B-TIC-468-UGR18Proyecto del Plan Nacional I + D: PID2019–104888GB-I00 and Proyectos I + D + i Junta de Andalucía 2018: P18-RT-3237H2020 ELICSIR project (grant No. 857558)Grant IJC2020-043307-I funded by MCIN/AEI/ 10.13039/501100011033European Union NextGenerationEU/ PRT

Development and characterization of remote radiation dosimetry systems using optically stimulated luminescence of Al2O3:C and KBr:Eu

Scope and Method of Study: To develop and test the performance of two different dosimetry systems; one for in situ, high-sensitivity, inexpensive environmental monitoring, and another for near-real-time medical dosimetry. The systems are based on remote interrogation of the optically stimulated luminescence (OSL) from Al2O3:C and KBr:Eu single crystal dosimeters (exposed to environmental and medical radiation fields, respectively) via fiber optic cables. The environmental system was tested in lab conditions using various radioactive sources including 60 Co, 90 Sr, 137 Cs, and 226 Ra, as well as with 232 Th-enriched soil stimulant. The medical system was tested under various diagnostic x-ray systems, including fluoroscopy and computed tomography (CT) machines, as well as with high dose rate 192 Ir brachytherapy sources and 232 MeV proton therapy beams under simulated treatment conditions.Findings and Conclusions: The environmental system was shown to achieve sensitivity high enough for measuring an OSL signal resulting from a dose of ~1 uGY, which is equivalent to ~12 hours of natural background radiation. This sensitivity allows for monitoring of the radiation characteristics of a natural environment more rapidly and/or less expensively than existing methods, such as soil sampling and in situ gamma spectroscopy. The KBr:Eu-based medical system results show that the near-real-time data acquisition during irradiation allows for rapid quality assurance (QA) measurements that benefits from high spatial resolution. These features are not present in most current standard dosimeters such as thermoluminescent detectors and pencil ionization chambers. The dosimeter does exhibit energy dependence, and a sensitization during high dose rate procedures. As a result, a model has been proposed that provides a description of the possible mechanisms that govern the transfer of electrons and holes within KBr:Eu during OSL measurement at room temperature. Correction factors for these effects must be investigated for the system to become relevant for accurate dosimetry, rather than rapid QA

Desenvolvimento de um dosímetro in vivo a MOSFET para aplicações em radioterapia

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2013.Na radioterapia (teleterapia), a diferença entre a dose prescrita e a dose recebida pelo paciente deve ser de no máximo 5%. Por esta razão o uso de dosímetros é essencial para atingir esta especificação e garantir o sucesso deste tipo de tratamento contra o câncer. Neste trabalho é apresentado um dosímetro in vivo a MOSFET para aplicações radioterápicas que possui um processo de leitura simples e preciso e que utiliza um sensor pequeno e de baixo custo. Além disso, este dosímetro não requer cabos ou baterias durante a irradiação o que é vantajoso, pois os metais presentes nestes componentes interagem com a radiação podendo assim alterar o valor da dose recebida pelo paciente. No dosímetro desenvolvido foi utilizado o circuito integrado (CI) CD4007UBM (Texas Instruments) como sensor de radiação. A sua escolha é justificada, pois seus transistores MOS possuem um óxido de porta com espessura de 120nm. Esta espessura é indicada para a aplicação desejada, pois tem uma sensibilidade à radiação ionizante próxima de 7 mV/Gy e permite a operação com tensões relativamente baixas, |VT| 1,6 V. Além disso, este CI é de muito baixo custo (R$1/CI) e possui dimensões reduzidas (área de 35mm2 e espessura inferior a 2 mm). Em um dosímetro a MOSFET a dose total é inferida pela variação da tensão de limiar (VT) devido à radiação ionizante, deste modo o circuito extrator de VT é um bloco fundamental deste tipo de dosímetro. No dosímetro desenvolvido foi utilizado um circuito extrator com corrente constante (CC) preciso, com baixo consumo e que determina diretamente o valor de VT. É importante mencionar que este extrator CC opera na inversão moderada (enquanto extratores CC convencionais são polarizados na inversão forte) e extrai um valor de VT que possui significado físico. Os experimentos com radiação ionizante foram realizados no Centro de Pesquisas Oncológicas (CEPON) em Florianópolis utilizando aceleradores lineares para gerar raios-X de 6 MV e 15 MV. Dentre os principais resultados do protótipo do dosímetro MOSFET CD4007 podemos citar: sensibilidade de 98,1 mV/Gy, dependência térmica de 0,5 cGy/°C, dependência angular de 13$0.5/IC, and small dimensions (35 mm2 and thickness lower than 2 mm). MOSFET dosimeters sense the total dose by the variation of the threshold voltage (VT ) due to ionizing radiation; for this reason, the VT -extractor circuit is a fundamental block in this type of dosimeter. In our dosimeter we used an accurate and lowpower constant-current (CC) VT -extractor circuit that directly determines the VT . It is worth to mention that this CC extractor operates in moderate inversion (conventional CC extractors are biased in strong inversion) and extracts a value of VT that has physical meaning. Experiments with ionizing radiation were carried out at the Centro de Pesquisas Oncol´ogicas (CEPON) in Florian´opolis/Santa Catarina using linear accelerators to generate X rays of 6 MV and 15 MV. Among the main results of the CD4007 MOSFET dosimeter we can highlight: radiation sensitivity 98.1 mV/Gy, thermal dependence 0.5 cGy/?C, angular dependence of 13%, energy dependence of 1.3%, linearity of 97.5%, and attenuation to the radiation beam of 0.14%

Conception of a Tissue Equivalent Plastic Dosimeter Using Scintillating Fibres for Hadronic Therapy and Space Radiation Effects Studies

Radiotherapy, and more specifically, proton therapy, presents a state-of-the-art treatment for many types of cancer. Although this relatively new approach to cancer treatment is enticing, it needs to be carefully monitored as it can result in unwanted severe sideeffects. The control of the treatment depends on test phases, namely to determine the dose to be deposited at the site, as well as on equipment that monitors the particle beam during treatment, a beam profile monitor, which verifies the stability of the intensity and position of the beam, its range and its straggling effect. This work proposes using scintillating fibres in the assembly of an equipment that allows measurements both for dose determination, as well as for beam monitor profile aplications. Plastic fibres in dosimetry present many advantages such as that gas is not required, the scintillation decay time is typically on the order of a few nanoseconds, the tissue equivalent characteristics of plastic, the spatial granularity is proportional to the fibre diameter and the signal amplitude is proportional to the deposited energy in the fibres. Though this linearity does not happen near the Bragg peak due to quenching, a typical effect in scintillating materials. Another issue is the crosstalk effect between adjacent fibres. Therefore this work is the beginning of a characterization study to learn about the fibre’s properties and evaluate their use in detectors for hadronic therapy and space effects studies. Given the complexity of the problem few results were obtained, nevertheless several iteration of Monte Carlo simulations are performed, we successfully measure the attenuation coefficient of the fibres as we also create a tray in order to quantify the crosstalk effect between adjacent fibres

Evaluation of the region-specific risks of accidental radioactive releases from the European Spallation Source

The European Spallation Source (ESS) is a neutron research facility under construction in southern Sweden. The facility will produce a wide range ofradionuclides that could be released into the environment. Some radionuclides are of particular concern such as the rare earth gadolinium-148. In this article, the local environment was investigated in terms of food production and rare earth element concentration in soil. The collected data will later be used to model thetransfer of radioactive contaminations from the ESS

A new standard in testing mattresses for use in x-ray imaging : developing, validating and using a novel method to test x-ray mattresses for pressure ulcer development, radiation dosimetry and image quality

Background In hospitals, patients often undergo X-ray imaging while lying on a mattress. Therefore, mattresses must have low X-ray attenuation properties to minimise radiation dose to the patient. Mattresses should create no artifacts within the X-ray image, as this may compromise image quality and diagnosis. Finally, mattresses should be constructed in such a way that interface pressure (IP) is minimized, limiting the chance of pressure ulcer formation. Aim For evaluating X-ray imaging table mattresses, this thesis has three aims (1). to develop and validate an anthropomorphic-phantom-based method of assessing X-ray table mattress IP as an index of mattress performance; (2) to assess X-ray table mattress pressure redistribution properties; and (3) to evaluate mattress radiation attenuation characteristics and their impacts on image quality. Methods and Materials An anthropomorphic phantom, simulating adult head, pelvis, and heels, was 3D-printed from X-ray computed tomography (CT) image data. Dry sand was added to represent 5 human weights and XSensor technology was used to assess pressure distribution. Phantom mattress IP characteristics were compared for the 5 weights against 27 sets of human mattress IP data to achieve phantom validation. Twenty-four X-ray table mattresses, 21 thinner and 3 thicker were assessed. Anthropomorphic phantom and Xsensor mattress interface pressure measurements were conducted for head, pelvis and heels, with and without X-ray table mattresses. Image quality and radiation attenuation were also assessed. Incident air kerma (IAK) was measured, with and without mattress, over a range of exposure factors using a digital dosimeter. Inverse image Quality Factor (IQFinv) was calculated to assess image quality using a commercially available phantom (CDRAD). Results The anthropomorphic phantom proved suitable for use in this thesis - based on correlation coefficient R values, there was a good correlation for the 5 phantom weights between the phantom and human pressure data. (R values: head =0.993, pelvis =0.997, and heels =0.996). There were statistically significant differences (p<0.05) between peak pressure values with and without X-ray table mattress for head, pelvis and heels. Additionally, there were statistically significant differences (p<0.05) between the IP ratio values with and without X-ray table mattresses. The type and age of the mattresses also had an impact on peak pressure values and IP ratios. IAK and image quality measures were impacted by mattress addition. IAK values decreased because of attenuation, with IQFinv having worse image quality. There was a negative correlation between mattress age and IAK, meaning that older mattresses had higher attenuation properties. The clinical impact of this finding, for the potential for radiation increase, was insignificant. No correlation was found between image quality and age. Conclusion A novel method for testing X-ray mattress IP was established and validated in this thesis. This method could be valuable for aiding mattress design and development and subsequent testing when in clinical use. For new mattresses, peak pressure values and IP ratios were greatly reduced, compared with older ones. The impact mattresses had on radiation attenuation and image quality are clinically insignificant

Novel Semiconducting Materials and Thin Film Technologies for High Energy Radiation Detection

Nowadays the development of real-time ionizing radiation detection system operating over large areas is crucial. Increasing quest for flexible, portable, low cost and low power consumption sensors pushed the scientific community to look for alternative materials and technologies able to fulfill these new requirements. In this thesis the potentiality of organic semiconductors and metal oxides as material platforms for novel ionizing radiation sensors is demonstrated. In particular, organic semiconductors are human tissue-equivalent and this represents a unique and desirable property for the development of dosimeters to be employed in the medical field. The ionizing radiation sensors described in this thesis have been designed, fabricated and characterized during my PhD research and are realized onto polymeric foils leading to flexible devices operating at low voltages, in ambient condition and able to directly detect X-rays, gamma-rays and protons. Following the study of the properties and of the mechanisms of interaction between the radiation and the active layers of the sensors, several strategies have been adopted to enhance the efficiency of these detectors. X-rays dosimeters based on organic semiconductors have been realized presenting record sensitivity values compared with the state of the art for large area radiation detection. The unprecedentedly reported performance led to the possibility to testing these devices in actual medical environments. Moreover, the proof-of-principle demonstration of a dosimetric detection of proton beams by organic-based sensors is reported. Finally, a new sensing platform based on metal oxides is introduced. Combining the advantages of amorphous high mobility oxide semiconductors with a multilayer dielectric, novel devices have been designed, capable of providing a sensitivity one order of magnitude higher than the one shown by the standard RADFETs. Thanks to their unique properties, these sensors have been integrated with a wireless readout system based on a commercial RFID tag and its assessment is presented

Modelling and verification of doses delivered to deformable moving targets in radiotherapy

During the last two decades, advanced treatment techniques have been developed in radiotherapy to achieve more conformal beam targeting of cancerous lesions. The advent of these techniques, such as intensity modulated radiotherapy (IMRT), volumetric modulated arc radiothreapy (VMAT), Tomotherapy etc., allows more precise localisation of higher doses to complex-shaped target volumes, thereby sparing more healthy tissue. In this context, motion management is a critical issue in contemporary radiotherapy (RT). That anatomic structures move during respiration is well known and much research is presently being devoted to strategies to contend with organ motion. However, moving structures are typically regarded as rigid bodies. The fact that many structures deform as a result of motion makes their resultant dose distributions difficult to measure and calculate, and has not been fully accounted for. The potential for ineffective treatments that do not take into account motion and anatomic deformation is self-evident. This thesis addresses the pressing need to investigate dose distributions in targets that deform during and/or between treatments, to ensure robust calculations for dose accumulation and delivery, thus providing the most positive outcomes for patients. This involves the direct measurement of complex and re-distributed dose in deforming objects (an experimental model), as well as calculations of the deformed dose distribution (a mathematical model). The comparison thereof aims to validate the dose deformation technique, thereby to apply the method to a clinical example such as liver stereotactic body radiotherapy. To facilitate four-dimensional deformable dosimetry for both external beam radiotherapy and brachytherapy, methodologies for three-dimensional deformed dose measurements were developed and employed using radiosensitive polymer gel combined with a cone beam optical computed tomography (CT) scanner. This includes the development of a novel prototype deformable target volume using a tissue-equivalent, deformable gel dosimetric phantom, dubbed &amp;ldquo;defgel&amp;rdquo;. This can reproducibly simulate targets subject to a range of mass- and density-conserving deformations representative of those observable in anatomical targets. This novel tool was characterised in terms of its suitability for the measurement of dose in deforming geometries. It was demonstrated that planned doses could be delivered to the deformable gel dosimeter in the presence of different deformations and complex spatial re-distributions of dose in all three dimensions could be quantified. For estimating the cumulative dose in different deformed states, deformable image registration (DIR) algorithms were implemented to &amp;lsquo;morph&amp;rsquo; a dose distribution calculated by a treatment planning system. To investigate the performance of DIR and dose-warping technique, two key studies were undertaken. The first was to systematically assess the accuracy of a range of different DIR algorithms available in the public domain and quantitatively examine, in particular, low-contrast regions, where accuracy had not previously been established. This work investigates DIR algorithms in 3D via a systematic evaluation process using defgel suitable for verification of mass- and density-conserving deformations. The second study was a full three-dimensional experimental validation of the dose-warping technique using the evaluated DIR algorithm and comparing it to directly measured deformed dose distributions from defgel. It was shown that the dose-warping can be accurate, i.e. over 95% passing rate of 3D-gamma analysis with 3%/3mm criteria for given extents of deformation up to 20 mm For the application of evaluating patient treatment planning involving tumour motion/deformation, two key studies were undertaken in the context of liver stereotactic body radiotherapy. The first was a 4D evaluation of conventional 3D treatment planning, combined with 4D computed tomography, in order to investigate the extent of dosimetric differences between conventional 3D-static and path-integrated 4D-cumulative dose calculation. This study showed that the 3D planning approach overestimated doses to targets by &amp;le; 9% and underestimated dose to normal liver by &amp;le; 8%, compared to the 4D methodology. The second study was to assess a consequent reduction of healthy tissue sparing, which may increase risk for surrounding healthy tissues. Estimates for normal tissue complications probabilities (NTCP) based on the two dose calculation schemes are provided. While all NTCP were low for the employed fractionation scheme, analysis of common alternative schemes suggests potentially larger uncertainties exist in the estimation of NTCP for healthy liver and that substantial differences in these values may exist across the different fractionation schemes. These bodies of work have shown the potential to quantify such issues of under- and/or over-dosages which are quite patient dependent in RT. Studies presented in this work consolidate gel dosimetry, image guidance, DIR, dose-warping and consequent dose accumulation calculation to investigate the dosimetric impact and make more accurate evaluation of conventional 3D treatment plans. While liver stereotactic body radiotherapy (SBRT) was primarily concerned for immediate clinical application, the findings of this thesis are also applicable to other organs with various RT techniques. Most importantly, however, it is hoped that the outcomes of this thesis will help to improve treatment plan accuracy. By considering both computation and measurement, it is also hoped that this work will open new windows for future work and hence provide building blocks to further enhance the benefit of radiotherapy treatment