Study of Novel Techniques for Verification Irnaging and Patient Dose Reconstruction in External Bearn Radiation Therapy Geneviève Jarry Doctor of Philosophy Department of Physics McGill University Montreal, Quebee 2007-03-29 A thesis submitted to the faculty of graduate studies and researeh in partial fulfillment of the requirements of the degree of Doctor of Philosophy ©Geneviève Jarry 2006 Library and Bibliothèque et 1+1 Archives Canada Archives Canada Published Heritage Direction du Branch Patrimoine de l'édition 395 Wellington Street 395, rue Wellington Ottawa ON K1A ON4 Ottawa ON K1A ON4 Canada Canada Your file Votre référence ISBN: 978-0-494-32300-7 Our file Notre référence ISBN: 978-0-494-32300-7 NOTICE: AVIS: The author has granted a non­ L'auteur a accordé une licence non exclusive exclusive license allowing Library permettant à la Bibliothèque et Archives and Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par télécommunication ou par l'Internet, prêter, telecommunication or on the Internet, distribuer et vendre des thèses partout dans loan, distribute and sell th es es le monde, à des fins commerciales ou autres, worldwide, for commercial or non­ sur support microforme, papier, électronique commercial purposes, in microform, et/ou autres formats. paper, electronic and/or any other formats. The author retains copyright L'auteur conserve la propriété du droit d'auteur ownership and moral rights in et des droits moraux qui protège cette thèse. this thesis. Neither the thesis Ni la thèse ni des extraits substantiels de nor substantial extracts from it celle-ci ne doivent être imprimés ou autrement may be printed or otherwise reproduits sans son autorisation. reproduced without the author's permission. ln compliance with the Canadian Conformément à la loi canadienne Privacy Act some supporting sur la protection de la vie privée, forms may have been removed quelques formulaires secondaires from this thesis. ont été enlevés de cette thèse. While these forms may be included Bien que ces formulaires in the document page count, aient inclus dans la pagination, their removal does not represent il n'y aura aucun contenu manquant. any loss of content from the thesis. ••• Canada DEDICATION To the people l love: Suzel, AIdé, Marjolaine and David I~ ii ACKNOWLEDGEMENTS As l reread my thesis for the thousandth time l ponder on aIl of you who have guided and helped me in the last four years. First l wish to thank my supervisor, Dr. Frank Verhaegen, for his guidance. While supervising me, he gave me the freedom to work independently and to explore my own research interests. He gave me the opportunity to participate to various international meetings and in the pro cess l had the chance to expand my horizons, both professionaIly and culturally. l would also like to thank him for thoroughly reviewing this thesis; his comments and suggestions greatly improved the quality of my work. My appreciation go es to Dr. Jan Seuntjens who played the role of my supervisor for the first three months of my Ph.D. From that time forward, he was always there to listen to me, to discuss my pro ject and to help me. During my thesis l had the chance to collaborate with a team of researchers at the Princess Margaret Hospital in Toronto. l would like to thank Dr. David Jaffray for giving me this opportunity, Dr. Douglas Moseley for making me feel welcome and helping me with measurements, Dr. Jeffrey Siewerdsen for always being the first to answer mye-mails and for sharing his expertise on CBCT with me, and Sean Graham for helping me with the measurements. l also have to thank the medieal physicists working at the MGH who have taught me about clinical work. l would like to thank Dr. Slobodan Devie for answering my many questions on electron beam treatments and portal imagers, William Parker for iii introducing me to Cadplan, Michael Evans for helping me with electron beam mea­ surements, Russel Ruo for helping me with Corvus and IMRT treatment planning and Dr. Wamied Abdel-Rahman for maintaining the computer cluster. 1 would like to acknowledge the engineering team: Pierre Leger who helped me with understand­ ing better the portal imager and Joe Larkins who helped me with my computer more than once. 1 would like to acknowledge the amazing work of the technologists work­ ing at the CL21A and CL21B who have helped me throughout my different projects. My appreciation goes to Dr. Ervin Pogdorsak for maintaining the excellence of the Medical Physics program at McGill University. 1 would like to thank aIl of the students that have gone through the program in the last four years and with whom 1 have shared my joys and frustrations. More par­ /~. ticularly 1 would like to thank Gabriella, Danielle, Clarisse, Claude, Vicky, Matthieu, Caroline, Sara, Rumtin, Andrew, Magdalena, Charmaine, Kristin, and Arman for being not only colleagues but friends. 1 would like to thank Lalith who introduced me to the portal imager, Vicky who helped me with the electron beam modeling, Danielle who helped me with IMRT measurements, Matthieu who helped me with the kV unit modeling and Emily H. who spent a lot of time making sure the MC cluster worked. A special mention go es to Gabriella who had the patience to listen to me when my research was not going as weIl as 1 would have wished. She was always happy to help me with measurements with the CT scanner or with debugging a program. 1 would like to thank my mom and my dad who have always believed in me. 1 would like to thank my mom for making me believe that 1 can do anything 1 set my iv mind to, for spending hours helping me with my homeworks when l was growing up and, in the process, transferring her love for learning and teaching onto me. l would like to thank my dad for supporting me in doing what l like and showing me the importance of being professional in all aspects of my life. Thank you to my little sister Marjolaine, who is also my best friend, for being my biggest fan and making me laugh when everything was going wrong. l have to thank David not only for his love, his understanding and his patience but also for his concrete contribution to my work. l have to thank him for the time he took to read my papers, to listen to my presentations and to help me with computer and programming problems. l don't believe my work would have been the same without him in my life. Finally l acknowledge the different sources of funding l have received throughout my Ph.D. studies. The Ministère de la Santé et des Services Sociaux du Québec for the Bourse en Physique Médicale. The Fonds de la Recherche en Santé du Québec for a doctoral training award. McGill University for two Alma Matter travel grants and the National Cancer Institute of Canada for a travel grant. v ABSTRACT Treatment delivery verification is an essential step of radiotherapy. The purpose of this thesis is to develop new methods to improve the verification of photon and electron beam radiotherapy treatments. This is achieved through developing and testing (1) a way to acquire portal images during electron beam treatments, (2) a method to reconstruct the dose delivered to patients during photon beam treatments and (3) a technique to improve image quality in kilovolt age (kV) cone beam computed tomography (CBCT) by correcting for scattered radiation. The portal images were acquired using the Varian CL21EX linac and the Varian aS500 electronic portal imaging device (EPID). The EGSnrc code was used to model fully the CL21EX, the aS500 and the kV CBCT system. We demonstrate that portal images of electron beam treatments with adequate contrast and resolution can be produced using the bremsstrahlung photons portion of the electron beam. Monte Carlo (MC) calculations were used to characterize the bremsstrahlung photons and to obtain predicted images of various phantoms. The technique was applied on a head and neck patient. An algorithm to reconstruct the dose given to patients during photon beam radiotherapy was developed and validated. The algorithm uses portal images and MC simulations. The primary fluence at the detector is back-projected through the patient CT geometry to obtain a reconstructed phase space file. The reconstructed phase space file is used to calculate the reconstructed dose to the patient using MC simulations. The reconstruction method was validated in homogeneous and vi heterogeneous phantoms for conventional and IMRT fields. The scattered radiation present in kV CBCT images was evaluated using MC simulations. Simulated predictions of the scatter distribution were subtracted from CBCT projection images prior to the reconstruction to improve the reconstructed image quality. Reducing the scattered radiation was found to improve contrast and reduce shading artifacts. MC simulations, in combinat ion with experimental techniques, have been shown to be valuable tools in the development of treatment verification methods. The three novel methods presented in this thesis contribute to the improvement of radiotherapy treatment verification. They can potentially improve treatment outcome by ensuring a better target coverage. VIl ABRÉGÉ Dans cette étude, trois nouvelles façons d'améliorer la vérification des traite­ ments de radiothérapie sont développées et testées: (1) l'acquisition d'images por­ tales durant les traitements utilisant des faisceaux d'électrons, (2) la reconstruction de la dose administrée aux patients durant les traitements utilisant des faisceaux de photons et (3) l'amélioriation de la qualité des images du système kilovolt de tomo­ graphie à faisceau conique (kVTFC).