Intensity Modulated Radiation Therapy (IMRT) is a modern radiotherapy treatment technique used to obtain highly conformal dose distributions. The delivery of IMRT is commonly achieved through the use of a multileaf collimator (MLC). One of the hindrances at present to the widespread use of IMRT is the increased time required for its planning, delivery and verification. In this thesis one particular method of MLC based IMRT, known as Static Multileaf Collimator based IMRT (SMLC-IMRT), has been studied along with methods for improving it???s delivery efficiency. The properties of an MLC commonly used in SMLC-IMRT have been characterised. The potential ramifications of these properties on the dosimetric accuracy of the delivered IMRT field were also investigated. An Interactive Leaf Sequencing (ILS) program was developed that allowed for the manipulation and processing of intensity maps using a variety of methods. The objective of each method was to improve the delivery efficiency whilst maintaining the dosimetric quality of the IMRT treatment. The different methods investigated were collimator angle optimisation, filtration, and intensity level optimisation. The collimator was optimised by identifying the angle at which the minimum monitor unit???s (MU???s) were required when using a sliding-window delivery method. A Savitzky-Golay filter was applied to random intensity maps and suitable filtration parameters identified for filtering clinical IMRT fields, and the intensity levels were optimised based on a deviation threshold. The deviation threshold identified the acceptable level of difference tolerable between the original and modified intensity map. Several IMRT cases were investigated and the impact of each the methods on MU???s, segments and dose distribution observed. As the complexity of IMRT fields increases the dosimetric impact of the MLC properties increases. Complex SMLC-IMRT fields require longer delivery times due to the increased number of MU???s and segments. Collimator optimisation was shown to be a fast and effective means of improving delivery efficiency with negligible dosimetric change to the optimised plan. Modifying intensity maps by applying a filter and optimising the intensity levels did reduce the complexity and improve the delivery efficiency, but also required a dosimetric compromise of the optimised plan.

Intensity Modulated Radiation Therapy (IMRT) is a modern radiotherapy treatment technique used to obtain highly conformal dose distributions. The delivery of IMRT is commonly achieved through the use of a multileaf collimator (MLC). One of the hindrances at present to the widespread use of IMRT is the increased time required for its planning, delivery and verification. In this thesis one particular method of MLC based IMRT, known as Static Multileaf Collimator based IMRT (SMLC-IMRT), has been studied along with methods for improving it???s delivery efficiency. The properties of an MLC commonly used in SMLC-IMRT have been characterised. The potential ramifications of these properties on the dosimetric accuracy of the delivered IMRT field were also investigated. An Interactive Leaf Sequencing (ILS) program was developed that allowed for the manipulation and processing of intensity maps using a variety of methods. The objective of each method was to improve the delivery efficiency whilst maintaining the dosimetric quality of the IMRT treatment. The different methods investigated were collimator angle optimisation, filtration, and intensity level optimisation. The collimator was optimised by identifying the angle at which the minimum monitor unit???s (MU???s) were required when using a sliding-window delivery method. A Savitzky-Golay filter was applied to random intensity maps and suitable filtration parameters identified for filtering clinical IMRT fields, and the intensity levels were optimised based on a deviation threshold. The deviation threshold identified the acceptable level of difference tolerable between the original and modified intensity map. Several IMRT cases were investigated and the impact of each the methods on MU???s, segments and dose distribution observed. As the complexity of IMRT fields increases the dosimetric impact of the MLC properties increases. Complex SMLC-IMRT fields require longer delivery times due to the increased number of MU???s and segments. Collimator optimisation was shown to be a fast and effective means of improving delivery efficiency with negligible dosimetric change to the optimised plan. Modifying intensity maps by applying a filter and optimising the intensity levels did reduce the complexity and improve the delivery efficiency, but also required a dosimetric compromise of the optimised plan.

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京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第13032号 / 論医博第2114号 / 新制||医||1016(附属図書館) / 32990 / 横浜市立大学大学院医科学専攻 / (主査)教授 増永 慎一郎, 教授 坂井 義治, 教授 小川 修 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

Radiotherapy has become an ever more successful treatment option for cancer.Advances in imaging protocols combined with precise therapy devices suchas linear accelerators contribute towards millimeter precision of treatmentdelivery with far fewer side effects. The ultimate goal of radiotherapy is tomaximize tumor control while minimizing adverse effects to healthy tissues,more importantly organs at risk surrounding the tumor. External beamradiotherapy is currently on the brink of breaking a new frontier: MagneticResonance Imaging (MRI) guided tumor tracking. Here, a combined linearaccelerator and MRI system can be used to treat and follow the tumor duringirradiation, called Real-time Adaptive Radiotherapy (ART). Tailoring of thebeam shape, by means of the Multi-leaf Collimator (MLC) on the fly has thepotential to complete a fully automated radiotherapy process. Recent advances in Reinforcement Learning (RL), a sub field of artificialintelligence has pushed the frontiers further in sequential decision making processesfurther in various fields. In a MLC tracking scenario, we hypothesizethat an RL agent trained on real-time tumor delineations and dose informationcould fulfill a specified dosimetric criteria on the fly over the moving target.To investigate the feasibility of RL for MLC tracking further: we designeda simulator, devised an appropriate RL framework and interfaced them to aDeep Q-Network (DQN) algorithm. Our results demonstrate the feasibility of employing RL for MLC trackingalong with numerous design choices that need to be considered while developingsuch a system. We believe to have taken the first step to bridge MLCtracking and RL by proposing a closed loop solution using dose information.

In treatment of cancer using high energetic radiation the problem arises how to irradiate the tumor without damaging the healthy tissue in the immediate vicinity. In order to do this, intensity modulated radiation therapy (IMRT) is used. In this thesis, the general goal is to modulate the homogeneous radiation field delivered by an external accelerator using a multileaf collimator in comparison with beam modifying devices. In order to generate intensity modulated fields in a static mode with multileaf collimators, the heuristic algorithm of Galvin, Chen and Smith is used. This method aims at finding a segmentation with a small number of segments, taking account of mechanical constraints such as leaves can move only in one direction, on one row, the right and left leaves cannot overlap (Interleaf Collision) and also every element between the leaf and the side of the collimator to which the leaf is connected is also covered (no holes in leaves). During the implementation of the algorithm, the initial intensity matrix with the desired radiation rates is inserted and using essential transformations, a positive combination of special matrices, segments, corresponding to fixed positions of multileaf collimator are obtained. All calculations end with the superposition of segments which leads to the creation of the 3-D matrix that will be used to irradiate the tumor. The algorithm is implemented in C++. The calculations are fast and the procedure is user friendly. The model is implemented for the case of protection the spinal cord while treating a tumor in the neck area. Furthermore, dose distributions obtained with this model and beam modifying devices in the neck area were compared. / Κατά τη θεραπεία του καρκίνου με χρήση υψηλής ενέργειας ακτινοβολίας, πρόβλημα αποτελεί ο περιορισμός της ακτινοβολίας στον όγκο στόχο και ο περιορισμός της συμμετοχής του υγιούς ιστού, της γειτονικής περιοχής, στο ελάχιστο. Προκειμένου να επιλυθεί το πρόβλημα αυτό χρησιμοποιείται ακτινοθεραπεία με πεδία ακτινοβολίας διαμορφωμένης έντασης (Ιntensity Μodulated Radiαtion Therapy – IMRT), με τη βοήθεια των κατευθυντήρων πολλαπλών φύλλων (Multileaf Collimators- MLC). Στόχος της συγκεκριμένης διπλωματικής εργασίας είναι η διαμόρφωση του ομοιογενούς πεδίου ακτινοβολίας, που διανέμεται μέσω του γραμμικού επιταχυντή χρησιμοποιώντας κατευθυντήρα πολλαπλών φύλλων και η σύγκριση των αποτελεσμάτων της προσομοίωσης με τις συσκευές διαμόρφωσης δέσμης (Beam Modifying Devices). Προκειμένου να παραχθούν τα διαμορφωμένης έντασης πεδία ακτινοβολίας, σε στατική μορφή, χρησιμοποιήθηκε ο αλγόριθμος των Galvin, Chen και Smith. H μέθοδος αποσκοπεί στην τμηματοποίηση του πίνακα με τα επιθυμητά ποσοστά ακτινοβολίας σε έναν μικρό αριθμό τμημάτων “segments”, λαμβάνοντας υπόψιν μηχανικούς περιορισμούς. (i) Τα φύλλα δύναται να κινηθούν μόνο κατά μήκος μιας διεύθυνσης, (ii) σε μια γραμμή, το αριστερό και το δεξί φύλλο δεν μπορούν να επικαλυφτούν (Interleaf Collision) και (iii) κάθε στοιχείο μεταξύ του φύλλου και της πλευράς του διαμορφωτή, με την οποία είναι συνδεδεμένο, είναι πάντα καλυμμένο (Νo holes in leaves). Κατά την υλοποίηση του αλγορίθμου, εισάγεται ο αρχικός πίνακας με τα επιθυμητά ποσοστά ακτινοβολίας και με τη χρήσης κατάλληλων μετασχηματισμών, προκύπτει ένας συνδυασμός από ειδικούς πίνακες (segments), οι οποίοι αντιστοιχούν σε θέσεις των κατευθυντήρων πολλαπλών φύλλων και θα χρησιμοποιηθούν για την ακτινοβόληση του όγκου. Ο αλγόριθμος υλοποιήθηκε σε C++. Οι υπολογισμοί είναι γρήγοροι και η διεργασία είναι φιλική προς το χρήστη. Το μοντέλο υλοποιήθηκε για την περίπτωση προστασίας της σπονδυλικής στήλης κατά τη θεραπεία όγκου στην περιοχή του λαιμού. Τέλος, οι κατανομές δόσεις που προέκυψαν με την προαναφερθέν μοντέλο συγκρίθηκαν με αυτές των συσκευών διαμόρφωσης δέσμης.

En proton thérapie, la technique de balayage, permet de traiter efficacement le patient vis à vis de l'irradiation de la tumeur et la protection des tissus sains. Ces bénéfices dosimétriques peuvent cependant être grandement dégradés par les mouvements intra-fraction. Par conséquent, l'étude de méthodes d'atténuation ou d'adaptation est nécessaire. C'est pour cela, que nous avons développé un logiciel ”open-source” de calcul et d'évaluation de dose en 4D, MSPT (Motion Simulator for Proton Therapy), pour la technique de balayage. Son but est de mettre en avant l'impact des mouvements intra-fraction en calculant la répartition de dose dans le patient. En outre, l'utilisation de MSPT nous a permis de mettre au point et de proposer une nouvelle méthode d'atténuation du mouvement basée sur l'ajustement du poids du faisceau quand celui-ci balaye la tumeur. En photon thérapie, un enjeu principal pour les traitements délivrés à l'aide de collimateurs multi-lames (MLC) consiste à trouver un ensemble de configurations du MLC permettant d'irradier correctement la tumeur. L'efficacité d'un tel ensemble se mesure par le total beam-on time et le total setup time. Dans notre étude, nous nous intéressons à la minimisation de ces critères, d'un point de vue algorithmique, pour de nouvelles technologies de MLC: le MLC rotatif et le MLC à double couche. De plus, nous proposons un algorithme d'approximation pour trouver un ensemble de configurations minimisant le total beam-on time pour le MLC rotatif / In proton therapy, the delivery method named spot scanning, can provide a particularly efficient treatment in terms of tumor coverage and healthy tissues protection. The dosimetric benefits of proton therapy may be greatly degraded due to intra-fraction motions. Hence, the study of mitigation or adaptive methods is necessary. For this purpose, we developed an open-source 4D dose computation and evaluation software, MSPT (Motion Simulator for Proton Therapy), for the spot-scanning delivery technique. It aims at highlighting the impact of intra-fraction motions during a treatment delivery by computing the dose distribution in the moving patient. In addition, the use of MSPT allowed us to develop and propose a new motion mitigation strategy based on the adjustment of the beam's weight when the proton beam is scanning across the tumor. In photon therapy, a main concern for deliveries using a multileaf collimator (MLC) relies on finding a series of MLC configurations to deliver properly the treatment. The efficiency of such series is measured by the total beam-on time and the total setup time. In our work, we study the minimization of these efficiency criteria from an algorithmic point of view, for new variants of MLCs: the rotating MLC and the dual-layer MLC. In addition, we propose an approximation algorithm to find a series of configurations that minimizes the total beam-on time for the rotating MLC