京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20786号 / 理博第4330号 / 新制||理||1622(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 谷森 達, 教授 永江 知文, 教授 鶴 剛 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

In dieser Arbeit wird die Bildgebung durch eine Compton-Kamera zur Überwachung der Partikelstrahlentherapie erstmals an der Technischen Universität Dresden untersucht. Die inhärenten Beschränkungen der Methode wurden durch Berechnungen und Monte Carlo Simulationen studiert. Im Zuge dieser Untersuchungen erschien der Raumtemperatur-Halbleiter Cadmium Zink Tellurid als ein vielversprechendes Detektor-Material. Zur weiteren Untersuchung wurde eine einfache Compton-Kamera konstruiert bestehend aus einem Cadmium Zink Tellurid Detektor und einem ortsempfndlichen Szintillationsdetektor. Das System hat gezeigt, dass eine akkurate Bildgebung mit radioaktiven Punktquellen unter Laborbedingungen möglich ist. Weitere praktische Beschränkungen der Compton-Bildgebung unter Strahlbedingungen konnten durch Experimente an einem Protonen-Strahl hergeleitet werden. Durch die experimentellen Erfahrungen mit der in dieser Arbeit entwickelten Compton-Kamera konnten wertvolle Informationen gesammelt werden, die erlauben, die Bildrekonstruktion zu evaluieren und dazu beitragen, die weitere Forschung hin zu einer klinisch anwendbaren Compton-Kamera zu leiten. / This work presents the first efforts at the Dresden University of Technology to study the feasibility of Compton imaging as a modality to monitor ion beam radiation therapy. The inherent limitations of the method have been studied by means of calculation and Monte Carlo simulation. As a result, the room-temperature semiconductor cadmium zinc telluride appeared as a promising detector material for a clinical device. For more detailed investigation, a simple Compton camera has been constructed comprising a cadmium zinc telluride detector and a position sensitive scintillation detector. This system has proven that accurate imaging of radioactive point sources in the laboratory is feasible. More practical restrictions of Compton imaging in beam conditions have been derived through experiments at a proton facility. Through the experimental work with the Compton camera developed in this work, valuable information was gathered which allowed to test the image reconstruction and to direct the further research towards a clinical Compton camera system.

Medical imaging is a technique that allows us to visualize non surgically the internal structure of the human body in order to diagnose or treat medical conditions. It permits also monitoring of physical processes or functions of different organs inside the body. The medical imaging encompasses wide range of techniques based on different physical prin- ciples, including techniques using ionizing radiation. The quality of the images depends significantly on the quality of the used imaging detectors. There are many types of the detectors, from old analog devices (e.g. films) to fully digital detectors such as flat panels, that are the most widely used today. The newer technology is being developed and the techniques such as photon counting explored. However, the state of the art technology is the single photon counting, where the experimental detectors such as Medipix are able to count and process each individual photon. This works studies the properties, features and applications of the newest detector from the Medipix family Timepix3 in different imaging modalities. Firstly, a design of a new hardware readout interface for Timepix3 is presented together with data acquisition software and new analysis and calibration algorithms. Then, different applications of Timepix3 detector were explored: very...

In dieser Arbeit wird die Bildgebung durch eine Compton-Kamera zur Überwachung der Partikelstrahlentherapie erstmals an der Technischen Universität Dresden untersucht. Die inhärenten Beschränkungen der Methode wurden durch Berechnungen und Monte Carlo Simulationen studiert. Im Zuge dieser Untersuchungen erschien der Raumtemperatur-Halbleiter Cadmium Zink Tellurid als ein vielversprechendes Detektor-Material. Zur weiteren Untersuchung wurde eine einfache Compton-Kamera konstruiert bestehend aus einem Cadmium Zink Tellurid Detektor und einem ortsempfndlichen Szintillationsdetektor. Das System hat gezeigt, dass eine akkurate Bildgebung mit radioaktiven Punktquellen unter Laborbedingungen möglich ist. Weitere praktische Beschränkungen der Compton-Bildgebung unter Strahlbedingungen konnten durch Experimente an einem Protonen-Strahl hergeleitet werden. Durch die experimentellen Erfahrungen mit der in dieser Arbeit entwickelten Compton-Kamera konnten wertvolle Informationen gesammelt werden, die erlauben, die Bildrekonstruktion zu evaluieren und dazu beitragen, die weitere Forschung hin zu einer klinisch anwendbaren Compton-Kamera zu leiten.:Abstract/Zusammenfassung Illustration Index Index of Tables List of Abbreviations 0 Introduction 0.1 Motivation 0.2 Task 1 Physical Background 1.1 Interaction of Ionizing Radiation with Matter 1.1.1 Coherent Photon Scattering 1.1.2 Incoherent Photon Scattering 1.1.3 Complete Absorption in the Nuclear Electric Field 1.1.4 Pair Production 1.1.5 Total Photon Cross Section 1.1.6 Directly Ionizing Radiation 1.2 Prompt Gamma-rays from Nuclear Reactions 1.3 Detector Technology 1.3.1 Semiconductor Detectors 1.3.2 Scintillation Detectors 1.4 Compton Imaging 1.4.1 Image Formation 1.4.2 History and Application of Compton Cameras 1.5 Prompt Gamma-ray Imaging for In-vivo Dosimetry – Work of Other Groups 2 Design Study 2.1 Introduction 2.1.1 Emission Spectra – Available Data 2.2 Materials and Methods 2.2.1 Angular Resolution 2.2.2 Efficiency 2. Results 2.4 Conclusions 3 Prototype System 3.1 Overview 3.2 System Components 3.2.1 CdZnTe Detector and its Front-end-electronics 3.2.2 LSO Block-Detector 3.2.3 Mounting Frame 3.2.4 DAQ Hardware and Software 3.3 Results 3.3.1 Detector Performance 3.3.2 System Performance 3.4 Conclusions 4 Beam Experiments 4.1 Introduction 4.2 Materials and Methods 4.3 Results 4.3.1 Source Test 4.3.2 Beam Profile 4.3.3 Trigger Rate 4.3.4 Pixel Selection in the LSO 4.3.5 Phantom Measurement 4.4 Conclusions 5 Discussion Appendix A A.1 Technical Drawing of the CdZnTe Electrode Layout Bibliography Danksagung Erklärung / This work presents the first efforts at the Dresden University of Technology to study the feasibility of Compton imaging as a modality to monitor ion beam radiation therapy. The inherent limitations of the method have been studied by means of calculation and Monte Carlo simulation. As a result, the room-temperature semiconductor cadmium zinc telluride appeared as a promising detector material for a clinical device. For more detailed investigation, a simple Compton camera has been constructed comprising a cadmium zinc telluride detector and a position sensitive scintillation detector. This system has proven that accurate imaging of radioactive point sources in the laboratory is feasible. More practical restrictions of Compton imaging in beam conditions have been derived through experiments at a proton facility. Through the experimental work with the Compton camera developed in this work, valuable information was gathered which allowed to test the image reconstruction and to direct the further research towards a clinical Compton camera system.:Abstract/Zusammenfassung Illustration Index Index of Tables List of Abbreviations 0 Introduction 0.1 Motivation 0.2 Task 1 Physical Background 1.1 Interaction of Ionizing Radiation with Matter 1.1.1 Coherent Photon Scattering 1.1.2 Incoherent Photon Scattering 1.1.3 Complete Absorption in the Nuclear Electric Field 1.1.4 Pair Production 1.1.5 Total Photon Cross Section 1.1.6 Directly Ionizing Radiation 1.2 Prompt Gamma-rays from Nuclear Reactions 1.3 Detector Technology 1.3.1 Semiconductor Detectors 1.3.2 Scintillation Detectors 1.4 Compton Imaging 1.4.1 Image Formation 1.4.2 History and Application of Compton Cameras 1.5 Prompt Gamma-ray Imaging for In-vivo Dosimetry – Work of Other Groups 2 Design Study 2.1 Introduction 2.1.1 Emission Spectra – Available Data 2.2 Materials and Methods 2.2.1 Angular Resolution 2.2.2 Efficiency 2. Results 2.4 Conclusions 3 Prototype System 3.1 Overview 3.2 System Components 3.2.1 CdZnTe Detector and its Front-end-electronics 3.2.2 LSO Block-Detector 3.2.3 Mounting Frame 3.2.4 DAQ Hardware and Software 3.3 Results 3.3.1 Detector Performance 3.3.2 System Performance 3.4 Conclusions 4 Beam Experiments 4.1 Introduction 4.2 Materials and Methods 4.3 Results 4.3.1 Source Test 4.3.2 Beam Profile 4.3.3 Trigger Rate 4.3.4 Pixel Selection in the LSO 4.3.5 Phantom Measurement 4.4 Conclusions 5 Discussion Appendix A A.1 Technical Drawing of the CdZnTe Electrode Layout Bibliography Danksagung Erklärung

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20172号 / 理博第4257号 / 新制||理||1612(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 谷森 達, 教授 永江 知文, 教授 鶴 剛 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Traditionally, medical imaging techniques such as PET (positron emission tomography) and SPECT (single-photon emission computed tomography) have relied on mechanical collimators to detect the sources of photons. This limits the image's resolution and field of view. To improve upon this, Compton cameras have emerged as a promising alternative. The principle is to measure the angle of a photon scattered in the detector, which indicates the likely sources in the form of a cone culminating in the position of the interaction. The cones from multiple events may be superimposed in order to generate an image. The object of this work is to use list-mode likelihood methods to better reconstruct the source image from the data recorded by a simulated Compton camera in the case of a solid detector volume with good spatial- and energy resolution.  The results demonstrate an improvement of image quality for reconstructions of single point source and multiple extended sources. In addition, the results indicate that our used algorithm converges for point sources. The minimum number of measured events for accurate reconstruction for different source distributions remains to be determined, and the algorithm's ability to resolve closely adjacent sources should be investigated more.

Compton cameras localize γ-ray sources in 3D space by observing evidence of Compton scattering with detectors sensitive to ionizing radiation. This thesis proposes a software system for operating a novel Compton camera device comprised of Timepix3 detectors and Katherine readouts. To communicate with readouts using UDP-based protocol, a dedicated hardware library was developed. The presented software can successfully control the acquisition of multiple Timepix3 detectors and simultaneously process their measurements in a real-time setting. To recognize instances of Compton scattering among observed interactions, a chain of algorithms is applied with explicit consideration for a possibly high volume of measured information. Unlike alternate approaches, the presented work uses a recently published charge drift time model to improve its spatial resolution. In order to achieve localization of γ-ray sources, the software performs conical back projection into a discretized cuboid volume. Results of randomized evaluation with simulated data indicate that the presented implementation is correct and constitutes a viable method of γ-ray source localization in 3D space. Experimental verification with a prototype model is in progress.

L'hadronthérapie est une technique innovante de radiothérapie par ions carbone ou protons visant à améliorer les traitements actuels. La précision balistique accrue renforce la nécessité d'un contrôle du dépôt de dose, si possible en temps réel. Une manière de réaliser ce contrôle est de détecter avec une caméra Compton le gamma prompt émis lors des fragmentations nucléaires pendant l'irradiation du patient. Dans un premier temps, la géométrie de deux types de caméra Compton (double diffusion puis simple diffusion) a été optimisée par simulation Monte Carlo. Cette optimisation a été réalisée en étudiant la réponse des caméras à une source ponctuelle de photons avec un spectre en énergie réaliste. La réponse de la caméra optimisée à l'irradiation d'un fantôme d'eau par un faisceau d'ions carbone ou de protons a ensuite été simulée. Ces simulations ont tout d'abord été confrontées à des mesures effectuées avec un prototype de taille réduite. Ces mesures ont ensuite été utilisées pour évaluer les taux de comptage dans les détecteurs attendus en conditions cliniques. Dans la configuration actuelle de la caméra, ces taux sont élevés et les phénomènes d'empilement risquent d'être problématiques. Enfin, il est démontré que le dispositif étudié est sensible à un déplacement du pic de Bragg de plus ou moins 5 mm malgré les problèmes de coïncidences fortuites et malgré le bruit introduit par l'algorithme de reconstruction utilisé. / Ion beam therapy is an innovative radiotherapy technique using mainly carbon ion and proton irradiations. Its aim is to improve the current treatment modalities. Because of the sharpness of the dose distributions, a control of the dose if possible in real time is highly desirable. A possibility is to detect the prompt gamma rays emitted subsequently to the nuclear fragmentations occurring during the treatment of the patient. In a first time two different Compton cameras (double and single scattering) have been optimised by means of Monte Carlo simulations. The response of the camera to a photon point source with a realistic energy spectrum was studied. Then, the response of the camera to the irradiation of a water phantom by a proton beam was simulated. It was first compared with measurement performed with small-size detectors. Then, using the previous measurements, we evaluated the counting rates expected in clinical conditions. In the current set-up of the camera, these counting rates are pretty high. Pile up and random coincidences will be problematic. Finally we demonstrate that the detection system is capable to detect a longitudinal shift in the Bragg peak of +or- 5 mm, even with the current reconstruction algorithm.

Les travaux décrits dans cette thèse sont centrés sur la caractérisation et l’optimisation d’une camera Compton à phase unique au xénon liquide pour des applications médicales. Le détecteur a été conçu pour exploiter les avantages d’une technique d’imagerie médicale innovante appelée l’imagerie 3γ. Elle vise à l’obtention de la position en 3D d’une source radioactive avec une très haute sensibilité et une réduction importante de la dose administrée au patient. L’imagerie 3γ est basée sur la détection en coïncidence de 3 photons gamma émis par un émetteur spécifique (+β, γ), le 44Sc. Un premier prototype de camera Compton au xénon liquide a été développé par le laboratoire Subatech à travers le projet XEMIS (Xenon Medical Imaging System), pour démontrer la faisabilité de l’imagerie 3γ. Ce nouveau système de détection comporte un système de cryogénie avancé et une électronique front-end à très faible bruit qui fonctionne à la température du xénon liquide. Ce travail a contribué à la caractérisation de la réponse du détecteur et à l’optimisation de la mesure du signal d’ionisation. L'influence de la grille de Frisch sur le signal mesuré a été particulièrement étudiée. Les premières preuves de la reconstruction Compton en utilisant une source de ²²Na (β+, Eγ = 1.274 MeV) sont aussi rapportées dans cette thèse et valident la preuve de concept de la faisabilité de l’imagerie 3γ. Les résultats présentés dans cette thèse ont joué un rôle essentiel dans le développement d’une camera Compton au xénon liquide de grandes dimensions pour l’imagerie des petits animaux. Ce nouveau détecteur, appelée XEMIS2, est maintenant en phase de construction. / The work described in this thesis is focused on the characterization and optimization of a single-phaseliquid xenon Compton camera for medical imaging applications. The detector has been conceived to exploit the advantages of an innovative medical imaging technique called 3γ imaging, which aims to obtain aprecise 3D location of a radioactive source with high sensitivity and an important reduction of the dose administered to the patient. The 3γ imaging technique is based on the detection in coincidence of 3gamma rays emitted by a specific (+β, γ) emitter radionuclide,the 44Sc. A first prototype of a liquid xenon Compton camera has been developed by Subatech laboratory within the XEMIS (Xenon Medical Imaging System) project, to proof the feasibility of the 3γ imaging technique. This new detection framework is based on an advanced cryogenic system and an ultra-low noise front-end electronics operating at liquid xenon temperature. This work has contributed to the characterization of the detector response and the optimization of the ionization signal extraction. A particular interest has been given to the influence of the Frisch grid on the measured signals. First experimental evidences of the Compton cone reconstruction using asource of ²²Na (β+, Eγ = 1.274 MeV) are also reported in this thesis, which demonstrate the proof of concept of the feasibility of the 3γ imaging. The results reported in this thesis have been essential for the development of a larger scale liquid xenon Compton camera for small animal imaging. This new detector, called XEMIS2, is now in phase of construction.

Ion beam therapy is an innovative radiotherapy technique using mainly carbon ion and proton irradiations. Its aim is to improve the current treatment modalities. Because of the sharpness of the dose distributions, a control of the dose if possible in real time is highly desirable. A possibility is to detect the prompt gamma rays emitted subsequently to the nuclear fragmentations occurring during the treatment of the patient. In a first time two different Compton cameras (double and single scattering) have been optimised by means of Monte Carlo simulations. The response of the camera to a photon point source with a realistic energy spectrum was studied. Then, the response of the camera to the irradiation of a water phantom by a proton beam was simulated. It was first compared with measurement performed with small-size detectors. Then, using the previous measurements, we evaluated the counting rates expected in clinical conditions. In the current set-up of the camera, these counting rates are pretty high. Pile up and random coincidences will be problematic. Finally we demonstrate that the detection system is capable to detect a longitudinal shift in the Bragg peak of +or- 5 mm, even with the current reconstruction algorithm.