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This project assesses the four dimensional computed tomography (4DCT) capabilities of the Philips Brilliance Big Bore CT scanner (Philips Medical Systems, Cleveland, OH). A mechanical phantom imparts clinically relevant motions to acrylic spheres of various diameters. The size, shape, and position of these spheres, as measured with 4DCT, are compared to their true size, shape, and position. An evaluation of image quality is also performed. Maximum discrepancies between physical and imaged volumes, for all sphere sizes and motion ranges, did not exceed 2.6 mm (mean = 1.2 mm, standard deviation = 0.4 mm). For approximately tissue equivalent density objects, mean CT# in 4DCT images differed from those in standard clinical thoracic images by only a few Hounsfield units. Measured geometric precision along with the accuracy of mean CT#s observed in 4DCT phase images indicate that 4DCT is an appropriate imaging technique for treatment planning. / Medical Physics

One of the greatest challenges in achieving accurate positioning in head and neck radiotherapy is that the anatomy at and above the cervical spine does not act as a single, mechanically rigid body. Current immobilization techniques contain residual uncertainties that are especially present in the lower neck that cannot be reduced by setting up to any single landmark. The work presented describes the development of a radiotherapy friendly mostly-plastic 6D robotic platform for positioning independent landmarks, (i.e., allowing remote, independent positioning of the skull relative to landmarks in the thorax), including analysis of kinematics, stress, radiographic compatibility, trajectory planning, physical construction, and phantom measurements of correction accuracy. No major component of the system within the field of imaging or treatment had a measured attenuation value greater than 250 HU, showing compatibility with x-ray-based imaging techniques. Relative to arbitrary overall setup errors of the head (min = 1.1 mm, max = 5.2 mm vector error) the robotic platform corrected the position down to a residual overall error of 0.75 mm +/- 0.33 mm over 15 cases as measured with optical tracking. This device shows the potential for providing reductions to dose margins in head and neck therapy cases, while also reducing setup time and effort.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18867号 / 医博第3978号 / 新制||医||1008(附属図書館) / 31818 / 京都大学大学院医学研究科医学専攻 / (主査)教授 鈴木 実, 教授 黒田 知宏, 教授 富樫 かおり / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18452号 / 医博第3907号 / 新制||医||1004(附属図書館) / 31330 / 京都大学大学院医学研究科医学専攻 / (主査)教授 伊達 洋至, 教授 武田 俊一, 教授 富樫 かおり / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

The effectiveness of cancer treatment is compromised by the need to reduce the uncertainties originating from a variety of factors including tumor volume delineation, patient setup, and irregular physiologic motion. In particular, effective yet practical tumor motion management remains a major challenge in current external beam radiation therapy. Many strategies such as motion encompassment, breath-hold techniques, and respiratory gating have been proposed in the literature and implemented clinically. These methods have shown success in certain situations with different limitations. With the advent of image guided radiation therapy, real-time tumor tracking methods have become popular in clinics to proactively address the challenge with on-board tumor localization. Nevertheless, such techniques rely on surrogate signals and have been reported vulnerable to errors. In this dissertation, EGRT is proposed as a new modality for effective and practical management strategy of cancer treatment uncertainties. One implementation of EGRT is to use PET emissions in real-time for direct tumor tracking during radiation delivery. Radiation beamlets are delivered along PET lines of response by a fast rotating ring therapy unit consisting of a linear accelerator and PET detectors. A complete treatment scheme with capabilities of accurate tumor tracking and dose planning is proposed to implement this EGRT concept. Simulation studies with physical phantom, 4D digital patient model, and clinical patient datasets are carefully designed to evaluate the feasibility and performance of EGRT. We show that with the capabilities of achieving both tumor tracking and sophisticated intensity modulation, EGRT has the potential to enable an effective implementation of 4D radiation therapy with true biological targeting and other advantages.

Owing to the steep dose fall-off curves of high precision and accuracy radiation therapy (RT) modalities such as stereotactic body RT (SBRT), treatment plans with extraordinarily small margins to organs at risk (OARs), such as the spinal cord, has been made possible. With this development, patient movements during treatment, i.e. intrafraction motion (IFM), must be monitored more closely. This master thesis was aimed at developing an A-mode ultrasound prototype to detect the motions of the cervical spine as part of an IFM management (IFMM) system. Current IFMM systems have several drawbacks, including invasiveness and indirect measurements. The existing prototype was tested in order to identify areas of improvement. The prototype developed was equipped with a preconditioning circuit that retains the frequency information of the signal. Furthermore, software was developed based on wavelet filtering and enveloping using the Hilbert transform. Multiple logic algorithms were added in order to handle lost signals, competing echoes, echoes from soft tissues etc. The newly-developed prototype was found to have higher accuracy and precision than the pre-existing prototype. It was also more robust when measuring distance to the spine. A difficulty in segmenting the echo for bone arises for low quality signals. Therefore a compromise exists between setup time, including probe adjustment, and signal quality. Future work includes the manufacturing of a new neck rest to enable robust probe adjustment and fixation.

Le cancer pulmonaire est la principale cause de décès parmi tous les cancers au Canada. Le pronostic est généralement faible, de l'ordre de 15% de taux de survie après 5 ans. Les déplacements internes des structures anatomiques apportent une incertitude sur la précision des traitements en radio-oncologie, ce qui diminue leur efficacité. Dans cette optique, certaines techniques comme la radio-chirurgie et la radiothérapie par modulation de l'intensité (IMRT) visent à améliorer les résultats cliniques en ciblant davantage la tumeur. Ceci permet d'augmenter la dose reçue par les tissus cancéreux et de réduire celle administrée aux tissus sains avoisinants. Ce projet vise à mieux évaluer la dose réelle reçue pendant un traitement considérant une anatomie en mouvement. Pour ce faire, des plans de CyberKnife et d'IMRT sont recalculés en utilisant un algorithme Monte Carlo 4D de transport de particules qui permet d'effectuer de l'accumulation de dose dans une géométrie déformable. Un environnement de simulation a été développé afin de modéliser ces deux modalités pour comparer les distributions de doses standard et 4D. Les déformations dans le patient sont obtenues en utilisant un algorithme de recalage déformable d'image (DIR) entre les différentes phases respiratoire générées par le scan CT 4D. Ceci permet de conserver une correspondance de voxels à voxels entre la géométrie de référence et celles déformées. La DIR est calculée en utilisant la suite ANTs («Advanced Normalization Tools») et est basée sur des difféomorphismes. Une version modifiée de DOSXYZnrc de la suite EGSnrc, defDOSXYZnrc, est utilisée pour le transport de particule en 4D. Les résultats sont comparés à une planification standard afin de valider le modèle actuel qui constitue une approximation par rapport à une vraie accumulation de dose en 4D. / Pulmonary cancer is the main cause of death amongst all cancers in Canada with a prognosis of about 15% survival rate in 5 years. The efficiency of radiotherapy treatments is lower when high displacements of the tumors are observed, mostly caused by intrafraction respiratory motion. Advanced techniques such as radiosurgery and intensity-modulated radiotherapy treatments (IMRT) are expected to provide better clinical results by delivering higher radiation doses to the tumor while sparing the surrounding healthy lung tissues. The goal of this project is to perform 4D Monte Carlo dose recalculations to assess the dosimetric impact of moving tumors in CyberKnife and IMRT treatments using dose accumulation in deforming anatomies. Scripts developed in-house were used to model both situations and to compare the Monte Carlo dose distributions with those obtained with standard clinical plans. Displacement vectors fields are obtained from a 4D CT data set and a deformable image registration (DIR) algorithm which allows a voxel-to-voxel correspondence between each respiratory phase. The DIR is computed by the Advanced Normalization Tools (ANTs) software and is mostly based on diffeormophisms. A modified version of DOSXYZnrc from EGSnrc software, defDOSXYZnrc, is used to transport radiation through non-linear geometries. These results are then compared to a typical 3D plan to determine whether or not the current planification is a good approximation of the true 4D dose calculation.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18139号 / 医博第3859号 / 新制||医||1002(附属図書館) / 30997 / 京都大学大学院医学研究科医学専攻 / (主査)教授 武藤 学, 教授 武田 俊一, 教授 富樫 かおり / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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