Characterisation of a Novel Radiation Detector and Demonstration of a Novel Error Detection Algorithm for Application in Radiotherapy

Radiation detectors play an important role in radiology departments, particularly in relation to imaging and dosimetry. The significant advances achieved in material properties and high-quality electronic systems during previous decades has led to a continual expansion of their role and usage. In turn, this has had a concomitant impact upon the rapid progress of radiation detector technologies, specifically those utilised in medical imaging and dosimetry. This thesis aims to evaluate a radiation detector for a particular function, and to assess its suitability for said function within radiology and radiotherapy departments. Two novel radiation detectors, one for low energy imaging (kV) and another for radiotherapy (MV), are named Lassena (kV) and Lassena (MV) respectively. These detectors underwent an evaluation for the first time in order to assess their performance. Lassena (kV) was assessed in terms of image resolution and noise level to obtain the detective quantum efficiency (DQE) values representing image quality. DQE (0.5) values were 0.46-0.59 for three beam energies. Lassena (MV) was evaluated regarding its dosimetric properties, including linearity based on dose rate, reproducibility, and uniformity. Lassena (MV) has a high degree of short-term reproducibility, an acceptable pixel uniformity-response at high dose rates, and acceptable linearity with a coefficient of determination of 0.8624. Lassena (kV) displayed promising results whilst Lassena (MV) exhibited high sensitivity to radiation. A Monte Carlo system consisting of a linear accelerator and radiation detector was built and calibrated in order to assess dose verification applications within radiotherapy using a radiation detector. Anatomical changes during radiation therapy (such as parotid shrinkage and sinusitis for a nasopharyngeal case) were replicated. Analysis of computational EPID images started to warn of a risk of deviation from the planned dose at -26.3% volume loss of the parotid gland. This is most likely to happen in the third week of the treatment, however, the user must be aware of the limitations present due to anatomical overlapping and gamma analysis

Large area CMOS active pixel sensor x‐ray imager for digital breast tomosynthesis: Analysis, modeling, and characterization

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134791/1/mp2368.pd

Advanced tracking and image registration techniques for intraoperative radiation therapy

Mención Internacional en el título de doctorIntraoperative electron radiation therapy (IOERT) is a technique used to deliver radiation to the surgically opened tumor bed without irradiating healthy tissue. Treatment planning systems and mobile linear accelerators enable clinicians to optimize the procedure, minimize stress in the operating room (OR) and avoid transferring the patient to a dedicated radiation room. However, placement of the radiation collimator over the tumor bed requires a validation methodology to ensure correct delivery of the dose prescribed in the treatment planning system. In this dissertation, we address three well-known limitations of IOERT: applicator positioning over the tumor bed, docking of the mobile linear accelerator gantry with the applicator and validation of the dose delivery prescribed. This thesis demonstrates that these limitations can be overcome by positioning the applicator appropriately with respect to the patient’s anatomy. The main objective of the study was to assess technological and procedural alternatives for improvement of IOERT performance and resolution of problems of uncertainty. Image-to-world registration, multicamera optical trackers, multimodal imaging techniques and mobile linear accelerator docking are addressed in the context of IOERT. IOERT is carried out by a multidisciplinary team in a highly complex environment that has special tracking needs owing to the characteristics of its working volume (i.e., large and prone to occlusions), in addition to the requisites of accuracy. The first part of this dissertation presents the validation of a commercial multicamera optical tracker in terms of accuracy, sensitivity to miscalibration, camera occlusions and detection of tools using a feasible surgical setup. It also proposes an automatic miscalibration detection protocol that satisfies the IOERT requirements of automaticity and speed. We show that the multicamera tracker is suitable for IOERT navigation and demonstrate the feasibility of the miscalibration detection protocol in clinical setups. Image-to-world registration is one of the main issues during image-guided applications where the field of interest and/or the number of possible anatomical localizations is large, such as IOERT. In the second part of this dissertation, a registration algorithm for image-guided surgery based on lineshaped fiducials (line-based registration) is proposed and validated. Line-based registration decreases acquisition time during surgery and enables better registration accuracy than other published algorithms. In the third part of this dissertation, we integrate a commercial low-cost ultrasound transducer and a cone beam CT C-arm with an optical tracker for image-guided interventions to enable surgical navigation and explore image based registration techniques for both modalities. In the fourth part of the dissertation, a navigation system based on optical tracking for the docking of the mobile linear accelerator to the radiation applicator is assessed. This system improves safety and reduces procedure time. The system tracks the prescribed collimator location to solve the movements that the linear accelerator should perform to reach the docking position and warns the user about potentially unachievable arrangements before the actual procedure. A software application was implemented to use this system in the OR, where it was also evaluated to assess the improvement in docking speed. Finally, in the last part of the dissertation, we present and assess the installation setup for a navigation system in a dedicated IOERT OR, determine the steps necessary for the IOERT process, identify workflow limitations and evaluate the feasibility of the integration of the system in a real OR. The navigation system safeguards the sterile conditions of the OR, clears the space available for surgeons and is suitable for any similar dedicated IOERT OR.La Radioterapia Intraoperatoria por electrones (RIO) consiste en la aplicación de radiación de alta energía directamente sobre el lecho tumoral, accesible durante la cirugía, evitando radiar los tejidos sanos. Hoy en día, avances como los sistemas de planificación (TPS) y la aparición de aceleradores lineales móviles permiten optimizar el procedimiento, minimizar el estrés clínico en el entorno quirúrgico y evitar el desplazamiento del paciente durante la cirugía a otra sala para ser radiado. La aplicación de la radiación se realiza mediante un colimador del haz de radiación (aplicador) que se coloca sobre el lecho tumoral de forma manual por el oncólogo radioterápico. Sin embargo, para asegurar una correcta deposición de la dosis prescrita y planificada en el TPS, es necesaria una adecuada validación de la colocación del colimador. En esta Tesis se abordan tres limitaciones conocidas del procedimiento RIO: el correcto posicionamiento del aplicador sobre el lecho tumoral, acoplamiento del acelerador lineal con el aplicador y validación de la dosis de radiación prescrita. Esta Tesis demuestra que estas limitaciones pueden ser abordadas mediante el posicionamiento del aplicador de radiación en relación con la anatomía del paciente. El objetivo principal de este trabajo es la evaluación de alternativas tecnológicas y procedimentales para la mejora de la práctica de la RIO y resolver los problemas de incertidumbre descritos anteriormente. Concretamente se revisan en el contexto de la radioterapia intraoperatoria los siguientes temas: el registro de la imagen y el paciente, sistemas de posicionamiento multicámara, técnicas de imagen multimodal y el acoplamiento del acelerador lineal móvil. El entorno complejo y multidisciplinar de la RIO precisa de necesidades especiales para el empleo de sistemas de posicionamiento como una alta precisión y un volumen de trabajo grande y propenso a las oclusiones de los sensores de posición. La primera parte de esta Tesis presenta una exhaustiva evaluación de un sistema de posicionamiento óptico multicámara comercial. Estudiamos la precisión del sistema, su sensibilidad a errores cometidos en la calibración, robustez frente a posibles oclusiones de las cámaras y precisión en el seguimiento de herramientas en un entorno quirúrgico real. Además, proponemos un protocolo para la detección automática de errores por calibración que satisface los requisitos de automaticidad y velocidad para la RIO demostrando la viabilidad del empleo de este sistema para la navegación en RIO. Uno de los problemas principales de la cirugía guiada por imagen es el correcto registro de la imagen médica y la anatomía del paciente en el quirófano. En el caso de la RIO, donde el número de posibles localizaciones anatómicas es bastante amplio, así como el campo de trabajo es grande se hace necesario abordar este problema para una correcta navegación. Por ello, en la segunda parte de esta Tesis, proponemos y validamos un nuevo algoritmo de registro (LBR) para la cirugía guiada por imagen basado en marcadores lineales. El método propuesto reduce el tiempo de la adquisición de la posición de los marcadores durante la cirugía y supera en precisión a otros algoritmos de registro establecidos y estudiados en la literatura. En la tercera parte de esta tesis, integramos un transductor de ultrasonido comercial de bajo coste, un arco en C de rayos X con haz cónico y un sistema de posicionamiento óptico para intervenciones guiadas por imagen que permite la navegación quirúrgica y exploramos técnicas de registro de imagen para ambas modalidades. En la cuarta parte de esta tesis se evalúa un navegador basado en el sistema de posicionamiento óptico para el acoplamiento del acelerador lineal móvil con aplicador de radiación, mejorando la seguridad y reduciendo el tiempo del propio acoplamiento. El sistema es capaz de localizar el colimador en el espacio y proporcionar los movimientos que el acelerador lineal debe realizar para alcanzar la posición de acoplamiento. El sistema propuesto es capaz de advertir al usuario de aquellos casos donde la posición de acoplamiento sea inalcanzable. El sistema propuesto de ayuda para el acoplamiento se integró en una aplicación software que fue evaluada para su uso final en quirófano demostrando su viabilidad y la reducción de tiempo de acoplamiento mediante su uso. Por último, presentamos y evaluamos la instalación de un sistema de navegación en un quirófano RIO dedicado, determinamos las necesidades desde el punto de vista procedimental, identificamos las limitaciones en el flujo de trabajo y evaluamos la viabilidad de la integración del sistema en un entorno quirúrgico real. El sistema propuesto demuestra ser apto para el entorno RIO manteniendo las condiciones de esterilidad y dejando despejado el campo quirúrgico además de ser adaptable a cualquier quirófano similar.Programa Oficial de Doctorado en Multimedia y ComunicacionesPresidente: Raúl San José Estépar.- Secretario: María Arrate Muñoz Barrutia.- Vocal: Carlos Ferrer Albiac

Applications of Medical Physics

Applications of Medical Physics” is a Special Issue of Applied Sciences that has collected original research manuscripts describing cutting-edge physics developments in medicine and their translational applications. Reviews providing updates on the latest progresses in this field are also included. The collection includes a total of 20 contributions by authors from 9 different countries, which cover several areas of medical physics, spanning from radiation therapy, nuclear medicine, radiology, dosimetry, radiation protection, and radiobiology

'ACOUSTO-OPTIC SENSING FOR SAFE MRI PROCEDURES'

In this work, a novel sensor platform is developed for safer and more effective magnetic resonance imaging (MRI). This is achieved by tracking interventional devices, such as guidewires and catheters during interventional MRI procedures, and by measuring the radio frequency (RF) field to assess RF safety of patients with implants, such as pacemakers, during diagnostic MRI. The sensor is based on an acousto-optic modulator coupled with a miniature antenna. This structure is realized on an optical fiber which is immune to the RF field and eliminates the need for conducting lines. The acousto-optic modulator consists of a piezo-electric transducer and a fiber Bragg grating (FBG). The piezoelectric transducer is electrically connected to the miniature antenna and mechanically coupled to the FBG. Local RF signal received by the miniature antenna is converted to acoustic waves by the piezoelectric transducer. Acoustic waves change the grating geometry on the FBG, thus the reflected light from the FBG is modulated. For diagnostic imaging, short dipole antennas are used for sensing the local electric field, which is the primary cause of RF induced heating. For tracking purposes, small loop antennas are used for capturing local MRI signal which contains the location information. In this thesis, a comprehensive model for the acousto-optic modulator is developed and validated through sensitivity and linearity tests. Prototype RF field sensors are built and characterized: sensitivity of 1.36mV/nT and 98 μV/V/m with minimum detectable field strength of 8.2pT/√Hz and 2.7V/m/√Hz and dynamic range of 117dB/√Hz at 23MHz are achieved with 4mm single loop and 8mm short dipole antennas, respectively. These figures are competitive with commercial sensors with much larger form factors. Catheter tracking capability of the sensor under MRI is demonstrated in-vivo in swine in a 0.55T scanner using an 8F catheter in addition to phantom studies under 0.55T and 1.5T clinical MRI systems.Ph.D