Inter-crystal scatter in positron emission tomography: Identification techniques and effects on reconstructed images for AX-PET demonstrator

La PET es una técnica de imagen en medicina nuclear que permite la visualización in-vivo y en 3D de procesos funcionales en seres vivos. Un escáner PET mide los rayos gamma producidos al aniquilarse un positrón, el cual es emitido por un radioisótopo inyectado al paciente. La eficiencia del sistema es una característica crucial de los escáneres PET de alta resolución dedicados a la imagen del cerebro o de animales pequeños con el fin de obtener una imagen más fiel o de reducir la actividad del radiotrazador, y por consiguiente, la dosis inyectada al paciente. El objetivo de este trabajo de investigación es mejorar la eficiencia y calidad de imagen de un prototipo de escáner PET axial (AX-PET) sin comprometer la resolución espacial. El escáner AX-PET está diseñado para imagen del cerebro humano y consta de varios pisos de cristales centelleadores largos y finos, orientados axialmente, que son leídos individualmente por un fotomultiplicador de silicio. El diseño del detector permite la adquisición de eventos en los que un rayo gamma sufre múltiples interacciones en diferentes cristales: eventos de dispersión inter-cristal (ICS). A diferencia de los eventos más convencionales con una sola interacción (Golden), los eventos ICS son ambiguos debido al desconocimiento de la secuencia de interacción. Por ello, en esta investigación desarrollamos estrategias para la inclusión e identificación de eventos ICS para reconstrucción de imagen y evaluamos el impacto en la eficiencia del sistema y calidad de imagen. Diferentes algoritmos son empleados para seleccionar la primera interacción en un evento ICS basándose en cinemática Compton, sección eficaz de Klein-Nishina, etc., cada cual con una determinada tasa de identificación. Su rendimiento es analizado en base a imágenes reconstruidas de una fuente puntual y tres maniquíes diferentes a través de varias figuras de mérito como coeficiente de recuperación, relación contraste-ruido, visibilidad, etc. El análisis de datos muestra una contribución estadísticamente significante de eventos ICS a la eficiencia del sistema: la sensitividad mejora entre un 25% y 80% con respecto a sólo eventos Golden dependiendo del subtipo de ICS seleccionados para la reconstrucción. Los resultados de la inclusión de coincidencias ICS revelan el incremento de la relación señal-ruido y contraste-ruido, pero una ligera reducción de la resolución espacial incluso para el mejor algoritmo de identificación. En conclusión, el uso de eventos ICS para reconstrucción de imagen es prometedor para medidas de baja actividad (baja estadística), dado que aumenta significativamente la eficiencia del sistema y mejora la calidad de imagen sin perjuicio severo a la resolución espacial.Positron Emission Tomography (PET) is a nuclear medicine imaging technique that allows in-vivo 3D visualization of functional processes of the body. A PET scanner measures the gamma rays produced during the annihilation of a positron, which is emitted from a radioisotope injected to the patient. System efficiency is a crucial feature of high resolution PET scanners aimed at brain or small animal imaging in order to obtain a more faithful image or reduce the radiotracer activity, hence dose, injected to the patient. The aim of this research work is to improve the efficiency and image quality of an Axial PET scanner prototype (AX-PET) without jeopardizing spatial resolution. The AX-PET scanner is designed for human brain imaging and is based on several layers of long, thin, axially arranged scintillator crystals, which are individually readout by Silicon Photo Multipliers. The detector's design allows acquisition of events in which a gamma ray has multiple interactions in different crystals: inter-crystal scatter (ICS) events. In contrast with more standard single-hit (or Golden) events, ICS events are ambiguous as the interaction sequence is unknown. Therefore, in this investigation we develop strategies for the inclusion and identification of ICS events for image reconstruction and assess the impact on system efficiency and image quality. Different algorithms are used to select the first interaction in an ICS event based on Compton kinematics, Klein-Nishina cross section, etc., each with a certain identification rate. Their performance is analysed on the resulting reconstructed images of a point source and three different phantoms through several figures of merit such as recovery coefficient, contrast to noise ratio, visibility, etc. The data analysis shows a statistically significant contribution of ICS events to system efficiency: a sensitivity improvement between 25% and 80% in comparison with only Golden events depending on the ICS subtypes selected for the reconstruction. The results of the inclusion of ICS coincidences reveal an increase in signal and contrast to noise ratio, but a slight decrease of the spatial resolution even for the best identification algorithm. In conclusion, the use of ICS events for image reconstruction is promising for low activity measurements (low statistics), as it significantly increases the system efficiency and improves image quality without a serious decrease in spatial resolution

Nuclear methods for real-time range verification in proton therapy based on prompt gamma-ray imaging

Accelerated protons are excellent candidates for treating several types of tumours. Such charged particles stop at a defined depth, where their ionisation density is maximum. As the dose deposit beyond this distal edge is very low, proton therapy minimises the damage to normal tissue compared to photon therapy. Nonetheless, inherent range uncertainties cast doubts on the irradiation of tumours close to organs at risk and lead to the application of conservative safety margins. This constrains significantly the potential benefits of proton over photon therapy and limits its ultimate aspirations. Prompt gamma rays, a by-product of the irradiation that is correlated to the dose deposition, are reliable signatures for the detection of range deviations and even for three-dimensional in vivo dosimetry. In this work, two methods for Prompt Gamma-ray Imaging (PGI) are investigated: the Compton camera (Cc) and the Prompt Gamma-ray Timing (PGT). Their applicability in a clinical scenario is discussed and compared. The first method aspires to reconstruct the prompt gamma ray emission density map based on an iterative imaging algorithm and multiple position sensitive gamma ray detectors. These are arranged in scatterer and absorber plane. The second method has been recently proposed as an alternative to collimated PGI systems and relies on timing spectroscopy with a single monolithic detector. The detection times of prompt gamma rays encode essential information about the depth-dose profile as a consequence of the measurable transit time of ions through matter. At Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and OncoRay, detector components are characterised in realistic radiation environments as a step towards a clinical Cc. Conventional block detectors deployed in commercial Positron Emission Tomography (PET) scanners, made of Cerium-doped lutetium oxyorthosilicate - Lu2SiO5:Ce (LSO) or Bismuth Germanium Oxide - Bi4Ge3O12 (BGO) scintillators, are suitable candidates for the absorber of a Cc due to their high density and absorption efficiency with respect to the prompt gamma ray energy range (several MeV). LSO and BGO block detectors are compared experimentally in clinically relevant radiation fields in terms of energy, spatial and time resolution. On a different note, two BGO block detectors (from PET scanners), arranged as the BGO block Compton camera (BbCc), are deployed for simple imaging tests with high energy prompt gamma rays produced in homogeneous Plexiglas targets by a proton pencil beam. The rationale is to maximise the detection efficiency in the scatterer plane despite a moderate energy resolution. Target shifts, increase of the target thickness and beam energy variation experiments are conducted. Concerning the PGT concept, in a collaboration among OncoRay, HZDR and IBA, the first test at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with several detectors and heterogeneous phantoms is performed. The sensitivity of the method to range shifts is investigated, the robustness against background and stability of the beam bunch time profile is explored, and the bunch time spread is characterised for different proton energies. With respect to the material choice for the absorber of the Cc, the BGO scintillator closes the gap with respect to the brighter LSO. The reason behind is the high energies of prompt gamma rays compared to the PET scenario, which increase significantly the energy, spatial and time resolution of BGO. Regarding the BbCc, shifts of a point-like radioactive source are correctly detected, line sources are reconstructed, and one centimetre proton range deviations are identified based on the evident changes of the back projection images. Concerning the PGT experiments, for clinically relevant doses, range differences of five millimetres in defined heterogeneous targets are identified by numerical comparison of the spectrum shape. For higher statistics, range shifts down to two millimetres are detectable. Experimental data are well reproduced by analytical modelling. The Cc and the PGT are ambitious approaches for range verification in proton therapy based on PGI. Intensive detector characterisation and tests in clinical facilities are mandatory for developing robust prototypes, since the energy range of prompt gamma rays spans over the MeV region, not used traditionally in medical applications. Regarding the material choice for the Cc: notwithstanding the overall superiority of LSO, BGO catches up in the field of PGI. It can be considered as a competitive alternative to LSO for the absorber plane due to its lower price, higher photoabsorption efficiency, and the lack of intrinsic radioactivity. The results concerning the BbCc, obtained with relatively simple means, highlight the potential application of Compton cameras for high energy prompt gamma ray imaging. Nevertheless, technical constraints like the low statistics collected per pencil beam spot (if clinical currents are used) question their applicability as a real-time and in vivo range verification method in proton therapy. The PGT is an alternative approach, which may have faster translation into clinical practice due to its lower price and higher efficiency. A proton bunch monitor, higher detector throughput and quantitative range retrieval are the upcoming steps towards a clinically applicable prototype, that may detect significant range deviations for the strongest beam spots. The experimental results emphasise the prospects of this straightforward verification method at a clinical pencil beam and settle this novel approach as a promising alternative in the field of in vivo dosimetry.:1 Introduction 1.1 Proton therapy 1.1.1 The beginnings 1.1.2 Essential features 1.1.3 Advantages and drawbacks 1.2 Range uncertainties and their consequences 1.3 Range verification methods 1.4 Prompt gamma-ray imaging 1.4.1 Passive collimation 1.4.2 Active collimation 1.4.3 Correlation to dose 1.5 Aim of this work 2 Compton camera 2.1 Theoretical background 2.1.1 Compton formula and Klein-Nishina cross section 2.1.2 Detection principle 2.1.3 Intersection of cone surface and plane 2.1.4 Practical considerations 2.2 Motivation 2.3 Goals 2.4 Materials 2.4.1 Scintillator properties 2.4.2 Block detector properties 2.4.3 Electronics and data acquisition 2.4.4 High efficiency Compton camera setup 2.5 Experimental setup 2.5.1 Accelerators 2.5.2 Detector setup 2.5.3 Trigger regime 2.6 Methods 2.6.1 Energy calibration 2.6.2 Spatial calibration 2.6.3 Time calibration 2.6.4 Error analysis 2.6.5 Systematic measurement program 2.7 Results – absorber choice 2.7.1 Energy resolution 2.7.2 Spatial resolution 2.7.3 Time resolution 2.8 Discussion – absorber choice 2.9 Results – BbCc setup 2.10 Discussion – BbCc setup 3 Prompt gamma-ray timing 3.1 Theoretical background 3.1.1 Detection principle 3.1.2 Kinematics 3.1.3 Detector model 3.1.4 Quantitative assessment 3.2 Goals 3.3 Materials 3.3.1 Detectors 3.3.2 Electronics 3.3.3 Accelerators 3.4 Methods 3.4.1 Detector and module settings 3.4.2 Proton bunch phase stability 3.4.3 Proton bunch time structure 3.4.4 Systematic measurement program 3.4.5 Data acquisition rate 3.4.6 Data analysis 3.4.7 Modelling of PGT spectra 3.5 Results 3.5.1 Intrinsic detector time resolution 3.5.2 Illustrative energy over time spectra 3.5.3 Proton bunch phase stability 3.5.4 Proton bunch time structure 3.5.5 Systematic measurement program 3.6 Discussion 3.7 Conclusions 4 Discussion 4.1 Detector load, event throughput and spot duration 4.2 Comparison of PGI systems 4.3 Summary 4.4 Zusammenfassung BibliographyBeschleunigte Protonen sind ausgezeichnete Kandidaten für die Behandlung von diversen Tumorarten. Diese geladenen Teilchen stoppen in einer bestimmten Tiefe, bei der die Ionisierungsdichte maximal ist. Da die deponierte Dosis hinter der distalen Kante sehr klein ist, minimiert die Protonentherapie den Schaden an normalem Gewebe verglichen mit der Photonentherapie. Inhärente Reichweitenunsicherheiten stellen jedoch die Bestrahlung von Tumoren in der Nähe von Risikoorganen in Frage und führen zur Anwendung von konservativen Sicherheitssäumen. Dadurch werden die potentiellen Vorteile der Protonen- gegenüber der Photonentherapie sowie ihre letzten Ziele eingeschränkt. Prompte Gammastrahlung, ein Nebenprodukt der Bestrahlung, welche mit der Dosisdeposition korreliert, ist eine zuverlässige Signatur um Reichweitenunterschiede zu detektieren und könnte sogar für eine dreidimensionale in vivo Dosimetrie genutzt werden. In dieser Arbeit werden zwei Methoden für Prompt Gamma-ray Imaging (PGI) erforscht: die Compton-Kamera (CK) und das Prompt Gamma-ray Timing (PGT)-Konzept. Des Weiteren soll deren Anwendbarkeit im klinischen Szenario diskutiert und verglichen werden. Die erste Methode strebt nach der Rekonstruktion der Emissionsdichtenverteilung der prompten Gammastrahlung und basiert auf einem iterativen Bildgebungsalgorithmus sowie auf mehreren positionsempfindlichen Detektoren. Diese werden in eine Streuer- und Absorberebene eingeteilt. Die zweite Methode ist vor Kurzem als eine Alternative zu kollimierten PGI Systemen vorgeschlagen worden, und beruht auf dem Prinzip der Zeitspektroskopie mit einem einzelnen monolithischen Detektor. Die Detektionszeiten der prompten Gammastrahlen beinhalten entscheidende Informationen über das Tiefendosisprofil aufgrund der messbaren Durchgangszeit von Ionen durch Materie. Am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) und OncoRay werden Detektorkomponenten in realistischen Strahlungsumgebungen als ein Schritt zur klinischen CK charakterisiert. Konventionelle Blockdetektoren, welche in kommerziellen Positronen-Emissions-Tomographie (PET)-Scannern zum Einsatz kommen und auf Cer dotiertem Lutetiumoxyorthosilikat - Lu2SiO5:Ce (LSO) oder Bismutgermanat - Bi4Ge3O12 (BGO) Szintillatoren basieren, sind geeignete Kandidaten für den Absorber einer CK wegen der hohen Dichte und Absorptionseffizienz im Energiebereich von prompten Gammastrahlen (mehrere MeV). LSO- und BGO-Blockdetektoren werden in klinisch relevanten Strahlungsfeldern in Bezug auf Energie-, Orts- und Zeitauflösung verglichen. Weiterhin werden zwei BGO-Blockdetektoren (von PET-Scannern), angeordnet als BGO Block Compton-Kamera (BBCK), benutzt, um die Bildgebung von hochenergetischen prompten Gammastrahlen zu untersuchen, die in homogenen Plexiglas-Targets durch einen Protonen-Bleistiftstrahl emittiert werden. Die Motivation hierfür ist, die Detektionseffizienz der Streuerebene zu maximieren, wobei jedoch die Energieauflösung vernachlässigt wird. Targetverschiebungen, sowie Änderungen der Targetdicke und der Teilchenenergie werden untersucht. In einer Kollaboration zwischen OncoRay, HZDR and IBA, wird der erste Test des PGT-Konzepts an einem klinischen Protonenbeschleuniger (Westdeutsches Protonentherapiezentrum Essen) mit mehreren Detektoren und heterogenen Phantomen durchgeführt. Die Sensitivität der Methode hinsichtlich Reichweitenveränderungen wird erforscht. Des Weiteren wird der Einfluss von Untergrund und Stabilität des Zeitprofils des Strahlenbündels untersucht, sowie die Zeitverschmierung des Bündels für verschiedene Protonenenergien charakterisiert. Für die Materialauswahl für den Absorber der CK ergibt sich, dass sich BGO dem lichtstärkeren LSO Szintillator angleicht. Der Grund dafür sind die höheren Energien der prompten Gammastrahlung im Vergleich zum PET Szenario, welche die Energie-, Orts- und Zeitauflösung von BGO stark verbessern. Anhand von offensichtlichen Änderungen der Rückprojektionsbilder zeigt sich, dass mit der BBCK Verschiebungen einer punktförmigen radioaktiven Quelle erfolgreich detektiert, Linienquellen rekonstruiert und Verschiebungen der Protonenreichweite um einen Zentimeter identifiziert werden. Für die PGT-Experimente können mit einem einzigen Detektor Reichweitenunterschiede von fünf Millimetern für definierte heterogene Targets bei klinisch relevanten Dosen detektiert werden. Dies wird durch den numerischen Vergleich der Spektrumform ermöglicht. Bei größerer Ereigniszahl können Reichweitenunterschiede von bis zu zwei Millimetern detektiert werden. Die experimentellen Daten werden durch analytische Modellierung wiedergegeben. Die CK und das PGT-Konzept sind ambitionierte Ansätze zur Verifizierung der Reichweite in der Protonentherapie basierend auf PGI. Intensive Detektorcharakterisierung und Tests an klinischen Einrichtungen sind Pflicht für die Entwicklung geeigneter Prototypen, da der Energiebereich prompter Gammastrahlung sich über mehrere MeV erstreckt, was nicht dem Normbereich der traditionellen medizinischen Anwendungen entspricht. Im Bezug auf die Materialauswahl der CK wird ersichtlich, dass BGO trotz der allgemeinen Überlegenheit von LSO für die Anwendung im Bereich PGI aufholt. Wegen des niedrigeren Preises, der höheren Photoabsorptionseffizienz und der nicht vorhandenen Eigenaktivität erscheint BGO als eine konkurrenzfähige Alternative für die Absorberebene der CK im Vergleich zu LSO. Die Ergebnisse der BBCK, welche mit relativ einfachen Mitteln gewonnen werden, heben die potentielle Anwendung von Compton-Kameras für die Bildgebung prompter hochenergetischer Gammastrahlen hervor. Trotzdem stellen technische Beschränkungen wie die mangelnde Anzahl von Messereignissen pro Bestrahlungspunkt (falls klinische Ströme genutzt werden) die Anwendbarkeit der CK als Echtzeit- und in vivo Reichweitenverifikationsmethode in der Protonentherapie in Frage. Die PGT-Methode ist ein alternativer Ansatz, welcher aufgrund der geringeren Kosten und der höheren Effizienz eine schnellere Umsetzung in die klinische Praxis haben könnte. Ein Protonenbunchmonitor, höherer Detektordurchsatz und eine quantitative Reichweitenrekonstruktion sind die weiteren Schritte in Richtung eines klinisch anwendbaren Prototyps, der signifikante Reichweitenunterschiede für die stärksten Bestrahlungspunkte detektieren könnte. Die experimentellen Ergebnisse unterstreichen das Potential dieser Reichweitenverifikationsmethode an einem klinischen Bleistiftstrahl und lassen diesen neuartigen Ansatz als eine vielversprechende Alternative auf dem Gebiet der in vivo Dosimetrie erscheinen.:1 Introduction 1.1 Proton therapy 1.1.1 The beginnings 1.1.2 Essential features 1.1.3 Advantages and drawbacks 1.2 Range uncertainties and their consequences 1.3 Range verification methods 1.4 Prompt gamma-ray imaging 1.4.1 Passive collimation 1.4.2 Active collimation 1.4.3 Correlation to dose 1.5 Aim of this work 2 Compton camera 2.1 Theoretical background 2.1.1 Compton formula and Klein-Nishina cross section 2.1.2 Detection principle 2.1.3 Intersection of cone surface and plane 2.1.4 Practical considerations 2.2 Motivation 2.3 Goals 2.4 Materials 2.4.1 Scintillator properties 2.4.2 Block detector properties 2.4.3 Electronics and data acquisition 2.4.4 High efficiency Compton camera setup 2.5 Experimental setup 2.5.1 Accelerators 2.5.2 Detector setup 2.5.3 Trigger regime 2.6 Methods 2.6.1 Energy calibration 2.6.2 Spatial calibration 2.6.3 Time calibration 2.6.4 Error analysis 2.6.5 Systematic measurement program 2.7 Results – absorber choice 2.7.1 Energy resolution 2.7.2 Spatial resolution 2.7.3 Time resolution 2.8 Discussion – absorber choice 2.9 Results – BbCc setup 2.10 Discussion – BbCc setup 3 Prompt gamma-ray timing 3.1 Theoretical background 3.1.1 Detection principle 3.1.2 Kinematics 3.1.3 Detector model 3.1.4 Quantitative assessment 3.2 Goals 3.3 Materials 3.3.1 Detectors 3.3.2 Electronics 3.3.3 Accelerators 3.4 Methods 3.4.1 Detector and module settings 3.4.2 Proton bunch phase stability 3.4.3 Proton bunch time structure 3.4.4 Systematic measurement program 3.4.5 Data acquisition rate 3.4.6 Data analysis 3.4.7 Modelling of PGT spectra 3.5 Results 3.5.1 Intrinsic detector time resolution 3.5.2 Illustrative energy over time spectra 3.5.3 Proton bunch phase stability 3.5.4 Proton bunch time structure 3.5.5 Systematic measurement program 3.6 Discussion 3.7 Conclusions 4 Discussion 4.1 Detector load, event throughput and spot duration 4.2 Comparison of PGI systems 4.3 Summary 4.4 Zusammenfassung Bibliograph

Brachytherapy heterogeneity correction algorithm

El objetivo de este trabajo de investigación es el estudio de la influencia de heterogeneidades de los tejidos en la dosimetría de braquiterapia. En concreto, hemos desarrollado un algoritmo que tiene en cuenta las calcificaciones localizadas dentro de la próstata y corrige la dosis de referencia en agua. Este algoritmo está basado en un modelo analítico y es aplicable a Sistemas de Planificación del Tratamiento (TPS) comerciales. El modelo analítico tiene un fundamento teórico consistente, y se basa en los valores de referencia (caso homogéneo) y en la definición de una longitud efectiva, que transforma el recorrido dentro de la calcificación en distancias mayores. La energía depositada en el caso heterogéneo a lo largo de un cierto tramo está asociada con la energía depositada en agua a lo largo de un tramo mayor (escalado). Los resultados del algoritmo muestran un acuerdo significativo con la simulación de Monte Carlo completa teniendo en cuenta las calcificaciones. Se han comprobado satisfactoriamente diferentes geometrías y composiciones de la calcificación. El algoritmo también es aplicable a cualquier tipo de heterogeneidad o blindaje. El cálculo a tiempo real del algoritmo hace factible su utilización en la planificación clínica del tratamiento y permite por tanto su mejora.The aim of this research work is to study the influence of tissue heterogeneities in the dosimetry of brachytherapy. Specifically, we have developed an algorithm that takes into account calcifications located inside the prostate and corrects the reference dose in water. This algorithm is based on an analytical model and is applicable to commercial Treatment Planing Systems (TPS). The analytical model has a consistent theoretical background, and it is based on the values of reference (the homogeneous case) and on the definition of an effective path, which scales the distances inside the calcification into larger ones. The energy released in the heterogeneous case along a certain step is associated with the energy released in water along a longer (scaled) step. The results given by the algorithm show a remarkable agreement with the complete Monte Carlo simulations taking into account the calcifications. Several geometries and compositions of the calcification have been checked successfully. The algorithm is also applicable for any type of heterogeneity or shielding. The real-time calculation of the algorithm makes it feasible for use in clinical treatment planning and thus for improving its quality

Compact Method for Proton Range Verification Based on Coaxial Prompt Gamma-Ray Monitoring: a Theoretical Study

Range uncertainties in proton therapy hamper treatment precision. Prompt gamma-rays were suggested 16 years ago for real-time range verification, and have already shown promising results in clinical studies with collimated cameras. Simultaneously, alternative imaging concepts without collimation are investigated to reduce the footprint and price of current prototypes. In this paper, a compact range verification method is presented. It monitors prompt gamma-rays with a single scintillation detector positioned coaxially to the beam and behind the patient. Thanks to the solid angle effect, proton range deviations can be derived from changes in the number of gamma-rays detected per proton, provided that the number of incident protons is well known. A theoretical background is formulated and the requirements for a future proof-of-principle experiment are identified. The potential benefits and disadvantages of the method are discussed, and the prospects and potential obstacles for its use during patient treatments are assessed. The final milestone is to monitor proton range differences in clinical cases with a statistical precision of 1 mm, a material cost of 25000 USD and a weight below 10 kg. This technique could facilitate the widespread application of in vivo range verification in proton therapy and eventually the improvement of treatment quality

Informe de las prácticas externas: Calibración de SiPM del plano de trazas del detector NEXT1-EL

El objetivo de las prácticas externas realizadas en el Laboratorio de Reacciones Nucleares (IFIC) es familiarizarse con los sistemas de adquisición de datos de una cámara de Xenon gaseoso a alta presión (TPC), que es el elemento principal del experimento NEXT1-EL. Esta TPC es un prototipo de otra mayor que se instalará en el Laboratorio Subterráneo de Canfranc. En concreto, mis prácticas se han centrado en la caracterización y cálculo de ganancia de fotomultiplicadores de silicio (SiPM), detectores que se emplean en el plano de tracking de la TPC para visualizar la traza de las partículas ionizantes para poder hacer una selección topológica de los eventos de interés, candidatos a ser una desintegración doble beta sin neutrinos. Además, me he familiarizado con los elementos que forman el detector, el alto vacío, la detección de puntos de fuga, el aislamiento del ruido mediante una jaula de Faraday, el sistema de purificación y recirculación de gases así como el módulo que controla el alto voltaje de los tubos fotomultiplicadores y SiPM. También he aprendido a utilizar ROOT y programar scripts para el tratamiento de las medidas experimentales realizadas a lo largo de las prácticas

Heat Unit Requirements of “Flame Seedless” Table Grape: A Tool to Predict Its Harvest Period in Protected Cultivation

Greenhouse cultivation of table grapes is a challenge due to difficulties imposed by their perennial habit and chilling requirements. Despite difficulties, greenhouse cultivation allows ripening long before that in the open field. Nonetheless, for harvesting “Flame Seedless” in the most profitable periods, a cultural practices timetable has to be established. In this context, an estimation of development rate as a function of temperature becomes essential. This work puts forward a procedure to determine “Flame Seedless” threshold temperatures and heat requirements from bud break to ripening. “Flame Seedless” required an average of 1633 growing degree days (GDD) in the open field with a base temperature of 5 °C and an upper threshold temperature of 30 °C. Strikingly, only 1542 GDD were required within the greenhouse. This procedure forecast “Flame Seedless” ripening with an accuracy of three and six days in the open field and greenhouse, improving predictions based on the average number of days between bud break and ripening. The procedure to predict oncoming harvest date was found satisfactory, just four days earlier than the real date. If we used the typical meteorological year instead of the average year, then the prediction was greatly improved since harvest was forecast just one day before its occurrence

Towards clinical application of RayStretch for heterogeneity corrections in LDR permanent 125-I prostate brachytherapy

Purpose: RayStretch is a simple algorithm proposed for heterogeneity corrections in low-dose-rate brachytherapy. It is built on top of TG-43 consensus data, and it has been validated with Monte Carlo (MC) simulations. In this study, we take a real clinical prostate implant with 71 125I seeds as reference and we apply RayStretch to analyze its performance in worst-case scenarios. Methods and Materials: To do so, we design two cases where large calcifications are located in the prostate lobules. RayStretch resilience under various calcification density values is also explored. Comparisons against MC calculations are performed. Results: Dose-volume histogram-related parameters like prostate D90, rectum D2cc, or urethra D10 obtained with RayStretch agree within a few percent with the detailed MC results for all cases considered. Conclusions: The robustness and compatibility of RayStretch with commercial treatment planning systems indicate its applicability in clinical practice for dosimetric corrections in prostate calcifications. Its use during intraoperative ultrasound planning is foreseen

Simulation of electron transport and secondary emission in a photomultiplier tube and experimental validation

[EN] The electron amplification and transport within a photomultiplier tube (PMT) has been investigated by developing an in-house Monte Carlo simulation code. The secondary electron emission in the dynodes is implemented via an effective electron model and the Modified Vaughan¿s model, whereas the transport is computed with the Boris leapfrog algorithm. The PMT gain, rise time and transit time have been studied as a function of supply voltage and external magnetostatic field. A good agreement with experimental measurements using a Hamamatsu R13408-100 PMT was obtained. The simulations have been conducted following different treatments of the underlying geometry: three-dimensional, two-dimensional and intermediate (2.5D). The validity of these approaches is compared. The developed framework will help in understanding the behavior of PMTs under highly intense and irregular illumination or varying external magnetic fields, as in the case of prompt gamma-ray measurements during pencil-beam proton therapy; and aid in optimizing the design of voltage dividers with behavioral circuit models.This work was supported by Conselleria de Educación, Investigación, Cultura y Deporte (Generalitat Valenciana) under grant numbers CDEIGENT/2019/011 and CDEIGENT/2021/012. P. Martín-Luna is supported by the Ministerio de Universidades (Gobierno de España), Spain under Grant Number FPU20/04958. We thank Hamamatsu (V. Sánchez, D. Castrillo) for technical support and guidance; R. Carrasco (IFIC) and P. Wohlfahrt (Siemens Healthineers) for the CT scanning; D. Calvo and D. Real (KM3net-IFIC) for their LED test platform, the electronics and maintenance services at IFIC for excellent support; and K. Albiol, J. V. Casaña-Copado, A. Gallas Torreira, E. Lemos Cid, G. Pausch, A. Pazos Álvarez, E. Pérez Trigo, S. Rit, A. Ros, J. Roser, J. Stein, J. L. Taín and R. Viegas for useful discussions.Martín-Luna, P.; Esperante, D.; Fernández Prieto, A.; Fuster-Martínez, N.; García Rivas, I.; Gimeno, B.; Ginestar Peiro, D.... (2024). Simulation of electron transport and secondary emission in a photomultiplier tube and experimental validation. Sensors and Actuators A Physical. 365:1-10. https://doi.org/10.1016/j.sna.2023.11485911036

The Effects of Combined Pre and Postharvest Deficit Irrigation on Loquat Yield, Fruit Quality and Handling Aptitude

Loquat prices depend on fruit size and earliness. Earliness is improved by postharvest deficit irrigation (DI), without negative effects on fruit size. An optimization of postharvest DI strategies carried out by limiting the dry period led to greater harvest date advancement, but water savings were reduced. To further improve fruit earliness and quality and increase water savings, we combined pre and postharvest DI strategies. Treatments were T1: trees not irrigated during six weeks after harvest (no preharvest DI applied); T2: trees that, in addition to postharvest DI, were not watered from the rapid fruit growth phase to harvest (nine extra weeks of DI); T3: trees that, in addition to postharvest DI, were not watered from color break to harvest (six weeks of DI plus postharvest DI); and T4: trees that in addition to postharvest DI were not watered during rapid fruit growth, but were re-irrigated at color break (2–3 weeks of DI, depending on the season). Full-irrigated trees were grown for comparison. T1 saved 18% water with respect to full-irrigation, and advanced harvesting by 16 days. T2 saved more water, had an earlier harvest and produced a higher early yield. Shorter dry periods were beneficial to a lower extent. Fruit size was significantly diminished by T2, but not by T4. A major advantage of T3 and T4 was the better performance of fruit during handling and shelf life. T2 fruits were favored by panelists for their sweetness but criticized for their smaller size