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1
Sim, Jenny Hiow-Hui, and jenny som@med monash edu au. "Continuing professional development in medical radiation science: journey towards reflective practice in cyberspace." RMIT University. Medical Sciences, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20061201.102703.
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The study aimed to investigate how continuing professional development (CPD) activities, through the development of a CPD educational framework, can assist Medical Radiation Science (MRS) practitioners to engage in reflective practice while entrenched in a protocol driven workplace culture. The study, with action research as the chosen methodology, and used both quantitative and qualitative methodology, was divided into two phases. The first phase of data collection aimed to inform the researcher of the needs of the MRS profession. The second phase of the study involved the design and development of an educational framework for CPD, based on current theories of learning and teaching using the framework and data collected from the first phase of the study, an online module was developed. The objectives of the module were to increase participants' knowledge in breast planning in radiation therapy by assisting participants to engage in reflective practice. The cyclical process of action research was used to pilot the module twice with two groups of volunteer radiation therapists. The online module was evaluated using Kirkpatrick's four level evaluation model (Kirkpatrick, 1998; Guskey, 2000). Based on Boud et al.'s reflection model (1985), all participants showed evidence of action, affective and perspective outcomes. They also demonstrated successful development of lifelong learning attributes, were empowered and their learning had a positive impact in their workplace. They began to assume a more proactive role and increased clinical responsibilities, engaging colleagues in collaborative reflections and adopting evidence-based approaches in advancing workplace practices. The study shows that it is possible to assist MRS practitioners to engage in reflective practice within a CPD educational framework online. The study also shows the importance of reflective practice, lifelong learning and transformative learning in CPD. Reflective practice liberates and empowers participants, lifelong learning equips them to continue learning and transformative learning facilitates perspective transformation. Thus, an effective educational framework is one that adopts a holistic approach towards CPD, by incorporating reflective practice, lifelong learning and transformative learning. The educational framework adopted in the present study may be extrapolated to CPD programs in other MRS disciplines and other healthcare professions.
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Maresse, Sharon. "Australian medical radiation science graduates’ experiences of resilience during transition to professional practice." Thesis, Curtin University, 2014. http://hdl.handle.net/20.500.11937/1624.
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Health professionals experience adversity as they make the transition from student to independent practice. Resilience during transition to practice for the medical radiation sciences (MRS) is unexamined. A grounded-theory approach was used to explore resilience among new Australian MRS professionals, resulting in a theoretical conceptualisation of resilience as a process of evolution, with phases of impact, energising, maintaining momentum, achieving equilibrium, and beating inertia. Resilience can be fostered by educators, colleagues, employers and professional organisations.
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Sim, Jenny. "Profile of Medical Radiation Science Practitioners as Lifelong Learners: Implications for the Design of Undergraduate Programs." Thesis, Curtin University, 2000. http://hdl.handle.net/20.500.11937/85.
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Literature has shown the importance of lifelong learning in the training of today's workforce and the crucial role of Higher Education in preparing graduates for lifelong learning. The aim of the current study is to establish the profile of Medical Radiation Science (MRS) practitioners as lifelong learners and to examine the implications of these findings for MRS undergraduate programs in Australia. The study builds on Candy et. al.'s 1994 report, Developing Lifelong Learners through Undergraduate Education, by drawing on the report's profile of lifelong learners and the features of the undergraduate program that promote lifelong learning. This present study used both quantitative and qualitative approaches, including collating the stakeholders' views on lifelong learning via surveys, one-to-one interviews and focus group discussion.Findings from this study indicate that all stakeholders (MRS practitioners, Heads of MRS Departments, students and teaching staff) viewed lifelong learning to be relevant to the profession and are important attributes for MRS practitioners to attain. However, attributes that were directly related to clinical competencies were more highly valued than attributes which were perceived to be associated with learning competencies. For each of the 25 attributes surveyed, the actual level of attainment fell below the nominated level of importance. Furthermore, the workplace culture was found to be non-supportive of lifelong learning. All MRS courses in Australia promote lifelong learning as one of their course objectives. There is a general trend towards adopting teaching approaches that promote lifelong learning, while assessment methods that promote and evaluate lifelong learning attributes were lagging behind.These findings have implications for both the MRS workplace and the MRS undergraduate courses in Australia. There needs to be greater dialogue and collaboration between the MRS employers and the universities to address the gap identified in the attributes. A conceptual model integrating lifelong learning in the context of MRS has been introduced to circumnavigate the predicament felt by most respondents that clinical competency must take precedence over all other attributes. Selection criteria by employers for graduates who are entering the workplace for the first time serve as the vital link between the workplace and the universities. By incorporating lifelong learning attributes as an essential part of the selection criteria, students would come to see the relevance of lifelong learning in their undergraduate training. A learning portfolio can be used as a means of demonstrating that the appropriate learning has taken place. There needs to be a closer link between teaching and assessment by aligning the teaching of lifelong learning objectives and activities with the assessment methods. To this end, it is important that teaching staff must be provided with the appropriate professional support to cultivate lifelong learning attributes and to equip them with the appropriate facilitation skills, before the lecturers can be expected to adopt lifelong learning approaches. This research provides a snapshot of lifelong learning in the MRS profession and should assist in the implementation of lifelong learning strategies that would direct the future of the profession.
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Sim, Jenny. "Profile of Medical Radiation Science Practitioners as Lifelong Learners: Implications for the Design of Undergraduate Programs." Curtin University of Technology, Department of Medical Imaging Science, 2000. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=9597.
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Literature has shown the importance of lifelong learning in the training of today's workforce and the crucial role of Higher Education in preparing graduates for lifelong learning. The aim of the current study is to establish the profile of Medical Radiation Science (MRS) practitioners as lifelong learners and to examine the implications of these findings for MRS undergraduate programs in Australia. The study builds on Candy et. al.'s 1994 report, Developing Lifelong Learners through Undergraduate Education, by drawing on the report's profile of lifelong learners and the features of the undergraduate program that promote lifelong learning. This present study used both quantitative and qualitative approaches, including collating the stakeholders' views on lifelong learning via surveys, one-to-one interviews and focus group discussion.Findings from this study indicate that all stakeholders (MRS practitioners, Heads of MRS Departments, students and teaching staff) viewed lifelong learning to be relevant to the profession and are important attributes for MRS practitioners to attain. However, attributes that were directly related to clinical competencies were more highly valued than attributes which were perceived to be associated with learning competencies. For each of the 25 attributes surveyed, the actual level of attainment fell below the nominated level of importance. Furthermore, the workplace culture was found to be non-supportive of lifelong learning. All MRS courses in Australia promote lifelong learning as one of their course objectives. There is a general trend towards adopting teaching approaches that promote lifelong learning, while assessment methods that promote and evaluate lifelong learning attributes were lagging behind.These findings have implications for both the MRS workplace and the MRS undergraduate courses in Australia. There needs to be greater ++dialogue and collaboration between the MRS employers and the universities to address the gap identified in the attributes. A conceptual model integrating lifelong learning in the context of MRS has been introduced to circumnavigate the predicament felt by most respondents that clinical competency must take precedence over all other attributes. Selection criteria by employers for graduates who are entering the workplace for the first time serve as the vital link between the workplace and the universities. By incorporating lifelong learning attributes as an essential part of the selection criteria, students would come to see the relevance of lifelong learning in their undergraduate training. A learning portfolio can be used as a means of demonstrating that the appropriate learning has taken place. There needs to be a closer link between teaching and assessment by aligning the teaching of lifelong learning objectives and activities with the assessment methods. To this end, it is important that teaching staff must be provided with the appropriate professional support to cultivate lifelong learning attributes and to equip them with the appropriate facilitation skills, before the lecturers can be expected to adopt lifelong learning approaches. This research provides a snapshot of lifelong learning in the MRS profession and should assist in the implementation of lifelong learning strategies that would direct the future of the profession.
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Andersson, Kristina. "Evaluation of uncertainties in sub-volume based image registration : master of science thesis in medical radiation physics." Thesis, Umeå universitet, Institutionen för fysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-38638.
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Physicians often utilize different imaging techniques to provide clear, visual information about internal parts of the patient. Since the different imaging modalities give different types of information, the combination of them serves as a powerful tool while determining the diagnosis, planning of treatment or during therapy follow-up. To simplify the interpretation of the image information, image registration is often used. The goal of the registration is to put different images in a common coordinate system. It is essential that the registration between the images is accurate. Normalized Mutual Information (NMI) is a metric that quantifies the conformity between images. Even though NMI is a robust method it is often dominated by large structures as the external contour of the patient as well as by the structures of the bones. The prostate is an organ that does not have a fixed position relative to the other organs and host small amounts of image information. The accuracy of the registration is therefore limited with respect to the prostate when using the whole image volume. This master thesis investigates the possibility to restrict the part of the image used for registration to a small volume around the prostate with goal to receive a better registration of the prostate than if full sized images are used. A registration program, utilizing NMI, was written and optimized in MatLab. Four Magnetic Resonance (MR) series and one Computed Tomographic (CT) series where taken over the pelvic area of five patients with the diagnosis prostate cancer. The prostate were delineated by a physician. By adding margin to the delineations five different sized Regions of Interest (ROI) where created. The smallest ROI precisely covered the prostate while the largest covered the whole image. The deviation in Center of Mass (CoM) between the images and the Percentage Volume Overlap (PVO) were calculated and used as a measure of alignment. The registrations performed with sub-volumes showed an improvement compared to those that used full-volume while registering a MR image to another MR image. In one third of the cases a 2 cm margin to the prostate is preferable. A 3 cm margin is the most favorable option in another third of the cases. The use of sub-volumes to register MR images to CT series turned out to be unpredictable with poor accuracy. Full sized image registration between two MR image pairs has a high precision but, due to the motion of the prostate, poor accuracy. As a result of the high information content in the MR images both high precision as well as high accuracy can be achieved by the use of sub-volume registration. CT images do not contain the same amount of image information around the prostate and the sub-volume based registrations between MR and CT images are hence inconsistent with a low precision.
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Gunn, Therese. "The impact of virtual reality training on the clinical skill and confidence of medical radiation science students." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/209310/1/Therese_Gunn_Thesis.pdf.
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This study investigates the impact of virtual reality simulation training on medical radiation science students. It evaluates this by comparing clinical skills between students using traditional learning methods and those trained with the inclusion of the VR simulator and assesses the impact on student clinical confidence. This study's outcomes have highlighted the advantages of using such an innovative technique whilst demonstrating that the software itself is not enough to guarantee student learning. Instead, it requires purposeful inclusion into the curriculum with educators ensuring knowledge of the technology and appreciating the students' individual learning needs.
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Leghuel, Hatim A. "Radiation Backscatter of Zirconia." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1377012297.
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Lindqvist, Malcolm, and Gustav Eriksson. "Investigations of Electron Contamination in Photon Fluence Monitoring of Radiotherapy." Thesis, Uppsala universitet, Medicinsk strålningsvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-260659.
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During the last decades radiotherapy has made major improvements in accuracy and individualization of the treatment techniques. In this project the thickness of a tungsten filter has been optimized using both simulations and experiments in order to further reduce the uncertainty in the dose given to the patient. With the filter, a dosage with less uncertainty can be obtained and less electrons will strike the patient which means less skin damage. In the simulations a program called PENELOPE, has been used which uses Monte Carlo methods for electron and photons transports. The experiment has been done on real Linear Accelerators.
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Von, Aulock Maryna. "Brain compatible learning in the radiation sciences." Thesis, Peninsula Technikon, 2003. http://hdl.handle.net/20.500.11838/1549.
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Thesis (MTech (Radiography))--Peninsula Technikon, Cape Town, 2003Brain Compatible Learning (BCL), as its name suggests, is a type of learning which is aligned with how the human brain naturally learns and develops. BCL offers many different options and routes to learning as alternatives to conventional 'chalk and talk' methodologies. A BCL curriculum is planned to define the structure and content of a programme of learning, but it also provides opportunities for students to participate in activities, which encourage and enhance the development of an active and deep approach to learning. Using BCL approaches in the classroom thus creates both a stimulating and a caring environment for student learning. This project researches a BCL intervention in a Radiation Science course. The use of BCL techniques has tended to have been done predominantly in the social sciences; this research fills an important 'gap' in the research literature by examining how BCL might be implemented in a technical and scientific context. The research was conducted using an adapted Participatory Active Research methodology in which classroom interventions were planned (within a constructive framework), rather than implemented and then reflected on by all participants. The PAR method was supplemented with a series of detailed questionnaires and interviews. The broad findings of this study relate to students' experiences of BCL in Radiation Science in terms of 'process' and 'product" issues. In terms of process, or the methodology of BCL, students' responses were largely positive.
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Wassberg, Cecilia. "Ultraviolet Radiation and Squamous Cell Carcinoma in Human Skin." Doctoral thesis, Uppsala University, Department of Medical Sciences, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1479.
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Ultraviolet radiation (UVR) is a major risk factor for development of skin cancer. UVR-induced DNA damage and a dysfunctional p53 protein are important steps in the development of squamous cell carcinoman in human skin (SCC). The aim of the present investigation was to analyze incidence trends of SCC in Sweden, quantify the risk of second primary cancer after SCC and further analyze the effects of UVR and p53 protein in human skin in vivo and in vitro. The effect of photoprotection by sunscreens was also evaluated.
We found that the age-standardized incidence rate of SCC in Sweden increased substantially in both men and women during the period 1961-1995, especially in men and at chronically sun-exposed skin sites. Patients with SCC are also at increased risk of developing new primary cancers, especially in the skin, squamous cell epithelium, hematopoietic tissues and respiratory organs. In experimental studies in vivo and in vitro in human skin we observed that repair of UV-induced DNA damage appears to be more efficient in chronically sun-exposed skin despite a less uniform p53 response. Non-sun- exposed skin is more homogeneous with respect to the epidermal p53 response. Keratinocytes in skin exposed frequently to the sun may be prone to react more easily to cytotoxic stress. Two different modalities of photoprotection significantly reduced the amount of DNA damage and the number of p53-positive cells. In addition, we demonstrated that a well-defined system for in vitro culture of explanted skin provides an excellent alternative to in vivo experiments.
In conclusion, this study has increased our knowledge of SCC epidemiology in Sweden and of the effects of artificial and solar UVR and sunscreens on chronically sun-exposed and non-sun-exposed sites, respectively, of human skin.
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Audet, Chantal. "NMR-based radiation dosimetry using polymer solutions." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59996.
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The spin-spin and spin-lattice relaxation times of protons on polymers, T$ sb{ rm 1p}$ and T$ sb{ rm 2p}$, respectively, have been used to probe the absorbed dose of irradiated polymer solutions in which radiation-induced changes in polymer molecular weight, M$ sb{ rm n}$, occur. The M$ sb{ rm n}$ dependencies of T$ sb{ rm 1p}$ and T$ sb{ rm 2p}$, and of the water proton T$ sb{ rm 1w}$ for solutions of poly(ethylene oxide) (PEO) in D$ sb2$O and H$ sb2$O are presented. T$ sb{ rm 1p}$ and T$ sb{ rm 1w}$ are independent of M$ sb{ rm n},$ and T$ sb{ rm 2p}$ varies with M$ sb{ rm n}$ according to a specific inverse power dependence until low M$ sb{ rm n}$ when T$ sb2$ saturation occurs. The dose dependence of T$ sb{ rm 1p}$ and T$ sb{ rm 2p}$ measured for dilute solutions of PEO in D$ sb2$O reflects the dependence of M$ sb{ rm n}$ on dose. A novel semi-empirical model is proposed for the dose dependence of T$ sb{ rm 2p}$ which incorporates the measured M$ sb{ rm n}$ power dependence of T$ sb{ rm 2p}$ into a theoretical expression of the dose dependence of the M$ sb{ rm n}$. This expression is based on previous bulk polymer work and has been modified to hold for polymers in solution. The model can be fitted well to the T$ sb{ rm 2p}$ data measured for different doses, and the values of the fitting parameters agree with those expected from independent measurements. Practical aspects of the NMR/polymer dosimetry technique are also addressed.
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Merlin, Scott L. "Endothelin-1 and radiation-associated impotence." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0022/MQ50837.pdf.
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Wang, Yi Zhen 1965. "Photoneutrons and induced activity from medical linear accelerators." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81453.
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This study involves the measurement of the neutron equivalent dose ( NED) and the induced activity produced from medical linear accelerators. For the NED, various parameters such as the profile, field effects and energy responses were studied. The NED in a Solid Water(TM) phantom was measured and a new quantity, the neutron equivalent dose tissue-air ratio (NTAR), was defined and determined. Neutron production for electron beams was also measured. For the induced activity, comparisons were carried out between different linacs, fields and dose rates. The half life and activation saturation were also studied. A mathematical model of induced activity was developed to explain the experimental results. Room surveys of NED and induced activity were performed in and around a high energy linear accelerator room. Unwanted doses from photoneutrons and induced activity to the high energy linear accelerator radiotherapy staff and patient were estimated.
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Koirala, Nischal. "Access Blood Flow Measurement Using Angiography." Cleveland State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=csu153796812445051.
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Chakradeo, Shweta. "ROLE OF AUTOPHAGY IN THE RESPONSE OF HS578T BREAST TUMOR CELLS TO RADIATION." VCU Scholars Compass, 2012. http://scholarscompass.vcu.edu/etd/2919.
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Breast cancer is the most commonly observed cancer type in women and is the second leading cause of cancer death in women. Radiation can be used to debulk tumors prior to surgery as well as to treat patients after surgery and/or chemotherapy. Previous studies from our laboratory have shown that the anti –malarial drug chloroquine sensitizes breast cancer cell lines to radiation by suppression of autophagy which is a conservative catabolic process that can be cytoprotective. The scientific literature has demonstrated that many tumor cell systems undergo cytoprotective autophagy and that pharmacological or genetic inhibition of autophagy leads to other modes of cell death such as apoptosis. Acridine orange staining was used for determination of acidic vacuole formation, an indication of autophagy and DAPI/TUNEL staining was used to identify apoptotic cells. Our studies in Hs578t breast tumor cells show the lack of sensitization by chloroquine upon autophagy inhibition with minimal apoptosis when cells are treated with 5 × 2Gy radiation. The extent of apoptosis was not increased upon autophagy inhibition by Chloroquine as determined by DAPI/TUNEL assays and quantified by Flow Cytometry using AnnexinV/PI. The potential role of senescence in the effects of radiation in the Hs578t cells was determined with the use of β-Galactosidase dye staining for senescence. It appears from these studies that autophagy need not to be cytoprotective in all breast cancer cell lines. Additional studies are in progress to effort to identify the factors that might distinguish between cytoprotective and non-cytoprotective autophagy.
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Mann, Travis L. "Patient Awareness and Knowledge of Medically Induced Radiation Exposure." ScholarWorks, 2019. https://scholarworks.waldenu.edu/dissertations/7881.
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The level of knowledge and awareness among patients about the concepts and implications of medical radiation is unknown. The purpose of this qualitative, case study was to explore patients' awareness and knowledge of information regarding this topic from their perspectives. The health belief model provided the framework for the study. A total of 20 individuals were recruited using purposive sampling. All participants were above the age of 18 in central North Carolina and had undergone or are currently undergoing medical radiation exams. Data were collected using semistructured interviews and analyzed using Yin's 5-phased cycle, which involved compiling, disassembling, reassembling, interpreting, and concluding. According to study findings, patients were generally aware of the harmful effects and seriousness of medical radiation if uncontrolled. Patients also cited the importance of having the proper information and resources to educate oneself, being more careful with their bodies to avoid examinations with radiation, and hearing reports about individuals getting ill from medical radiation exposure as cues to action that may benefit patients who are about to undergo medical radiation exams. The findings of this study may contribute to positive social change by illustrating ways to improve information dissemination and involvement of patients in understanding medical radiation and its perceived risks. The results of this study may help health practitioners in developing strategies to encourage patients to discuss their medical radiation exposure concerns proactively.
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LeBlanc, Julie-Maude. "Interaction between cisplatin and radiation in the treatment of ovarian cancer cells." Thesis, University of Ottawa (Canada), 2003. http://hdl.handle.net/10393/26337.
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The A2780s is a cisplatin and radiation-sensitive human ovarian carcinoma cell line from which the more resistant variant, A2780cp, was derived. In vitro experiments on the radiosensitivity of these cells with different treatments may be representative of the in vivo radiosensitivity, and maybe of use to patients receiving radiotherapy. Therefore, many studies have been directed at evaluation of the inhibition of DNA repair in order to improve radiotherapy. Previous studies showed that drugs and hyperthermia are repair inhibitors increasing the effectiveness of radiation. Cisplatin can also radiosensitize the A2780s and A2780cp and inhibit the sublethal damage repair (SLDR) (Raaphorst et al., 1995a). In this study we found no radiosensitization in the A2780s and A2780cp cells when cisplatin is added immediately before or after radiation. When cisplatin was added 24 hours prior to radiation, no increase in cellular resistance (adaptive response) to radiation treatment was observed. On the other hand cisplatin induced resistance when added during a pulse dose rate (PDR of 1 Gy/h) radiation treatment.
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Sarfehnia, Arman. "The use of orthogonal bremsstrahlung beams for imaging in radiation therapy /." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99203.
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Since portal images are created by megavoltage, forward-directed bremsstrahlung beams, their image quality is inferior to that of images produced by kilovoltage beams. In this study, characteristics of orthogonal bremsstrahlung photons produced by megavoltage electron beams were studied and their suitability for radiotherapy imaging was evaluated. Orthogonal bremsstrahlung beams with kilovoltage effective energies can be obtained from megavoltage electrons striking low atomic number targets. A 10 MeV electron beam emerging out of the research port of a Varian Clinac-18 linac was made to strike carbon, aluminum and copper targets. Percentage depth dose and attenuation measurements of forward and orthogonal beams were performed, and experimental results were compared with Monte Carlo-calculated findings. Images of simple contrast objects taken using the orthogonal bremsstrahlung beams showed superior contrast levels in comparison to those produced by the forward beams.
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Stroian, Gabriela. "Optimized scanning procedures for 4D CT data acquisition in radiation therapy." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84077.
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The goal of conformal radiation techniques is to improve local tumor control through dose escalation to target volumes while at the same time sparing surrounding healthy tissue. Accurate target volume delineation is essential in achieving this goal to avoid inadequate tumor coverage and/or irradiation of an unnecessary volume of healthy tissue. Respiratory motion is known to be the largest intra-fractional organ motion and the most significant source of uncertainty in treatment planning for chest lesions. A method to minimize effects of respiratory motion is to use four-dimensional (4D) radiotherapy.A novel scanning procedure for 4D CT data acquisition is described in this work. Three single-slice helical scans are acquired simultaneously with the real-time tracking of several markers placed on a moving phantom. At the end of the three scans. CT data is binned into different respiratory phases according to the externally recorded respiratory signal and the scanned volume is reconstructed for several respiratory phases. The 4D CT images obtained show an overall improvement when compared to conventional CT images of a moving phantom.
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Kased, Azad, and Peter Quach. "A Questionnaire Study on Patient Knowledge on X-ray Radiation Effects on Human Health from Dental Radiographic Examination." Thesis, Umeå universitet, Institutionen för odontologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-143417.
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Swedish Radiation Safety Authority has suggested guide-lines regarding information to individuals who undergo radiographic examinations. The guide-lines concerns medical care but patients in dental care can also be expected to have a wish to be informed about ionizing radiation. The main objective was to find out the patient’s perception of their knowledge about x-ray radiation and if they have a need to know more about x-rays. A questionnaire study was performed at two public dental clinics in Sweden during a twomonth period in the summer 2016. Patients ≥ 18 years old who gave their consent to participate were included in the study. Of all 429 participants 44 % declared an average knowledge about x-ray radiation and 37 % of all participants declared an inadequate knowledge. A total of 54 % had been informed about x-ray and its effects. School was the most common information source. Approximately 76 % had the perception that dental x-ray radiation is not harmful. 51 % declared the need to know more about x-ray. Approximately 52 % declared no knowledge about natural background radiation and 59 % declared it valuable to know more about dental x-ray in relation to natural background radiation. The participants showed mixed opinion and perception about x-ray radiation. A majority of patients want to know more about x-ray radiation. The study did not identify any particular group(s) needing more information about x-ray radiation than what is included in the justification of the radiographic examination.
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Hristov, Dimitre H. "Development of techniques for optimization and verification of radiation treatments." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0021/NQ44454.pdf.
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Elliott, Adam S. "Investigation of properties of a new liquid ionization chamber for radiation dosimetry." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101120.
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Liquid ionization chambers have characteristics that can remedy some of the drawbacks of air-filled ionization chamber dosimetry: large sensitive volumes, fluence perturbations, and energy dependence. However, high ion recombination rates can be a significant problem in liquid chambers. In this work, we have investigated properties of a new liquid chamber, called the GLIC-03 (Guarded Liquid Ionization Chamber), including chamber stability, reproducibility, and establishing recombination corrections. The response varied by less than 1% over 10 hours, and was reproducible within 1.5% of the mean over different liquid fills. Recombination corrections were established, and were small for low dose rates and high voltages. The establishment of these characteristics allowed us to compare measurements of the GLIC-03 in a region of charged particle disequilibrium to those made with a diamond detector. Results show the GLIC-03's suitability as a high resolution detector.
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Stewart, Kristin J. "Accurate radiation dosimetry using liquid- or air-filled plane-parallel ionization chambers." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29576.
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To optimize delivery of radiation therapy treatments, accurate knowledge of absorbed dose in the clinical beam is essential. In this work we investigated issues related to the use of different types of ionization chambers for accurate radiation dosimetry. We determined values of Pwall at 60Co for plane-parallel chambers and used them to derive the conversion factors kecal k'R 50 or kQ for a 20 MeV electron beam. Our results agreed within 0.4% with kQ values given in the IAEA TRS-398 protocol, but differences of up to 1.8% were found between our kecalk' R50 values and those in the AAPM TG-51 protocol. We also investigated the behavior of two liquid-filled ionization chambers in megavoltage photon beams, examining stability, ion recombination and beam quality dependence. Methods for determining and correcting for recombination were investigated. Preliminary results show that the energy dependence of a liquid-filled chamber can typically be limited to less than 1% for megavoltage photon beams.
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Wilson, Eden. "Radiation Sensitization of Breast Cancer Cells by Vitamin D Through the Promotion of Autophagic Cell Death." VCU Scholars Compass, 2012. http://scholarscompass.vcu.edu/etd/370.
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Radiation therapy is a widely used tool in cancer therapy and is frequently offered as the first line of treatment for cancers of the breast. While radiotherapy is often initially effective in killing tumor cells or suppressing their growth, there are factors that confer tumor cell resistance to irradiation. Development of resistance may lead to disease recurrence despite the use of surgery, chemotherapy and radiation therapy. A primary goal of the studies in Dr. Gewirtz’s laboratory is to develop strategies to overcome resistance to radiation (and chemotherapy) in breast cancer, with the ultimate goal of preventing or attenuating disease recurrence. One of these approaches involves combining the active form of vitamin D, 1,25-di hydroxy vitamin D3 or its analogs with radiotherapy. Our proposed studies were designed to build upon and extend previous work from this laboratory focused on determining the nature of cell death when vitamin D3 is combined with ionizing radiation in breast tumor cells. Studies were extended to the wild type p53, estrogen receptor positive, ZR-75-1 breast cancer cell line. We were able to validate that vitamin D3 does in fact, sensitize ZR-75-1 breast cancer cells to radiation therapy and substantiate that autophagy is the mode of sensitization by vitamin D3. Interestingly, our experimental system demonstrated that autophagy can actually have dual roles. Specifically, inhibition of autophagy both enhanced sensitivity to radiation and attenuated radiation sensitization by 1,25D3. Moreover, this experimental model proved to be a useful tool in trying to distinguish the factors involved in cytoprotective and cytotoxic autophagy, as we were able to demonstrate a potential role of 5' adenosine monophosphate-activated protein kinase in the sensitization of breast tumor cells to radiation by vitamin D3 as well as cytotoxic autophagy.
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Rigaud, Gaël. "Study of generalized Radon transforms and applications in Compton scattering tomography." Phd thesis, Université de Cergy Pontoise, 2013. http://tel.archives-ouvertes.fr/tel-00945739.
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Since the advent of the first ionizing radiation imaging devices initiated by Godfrey Newbold Hounsfield and Allan MacLeod Cormack, Nobel Prizes in 1979, the requirement for new non-invasive imaging techniques has grown. These techniques rely upon the properties of penetration in the matter of X and gamma radiation for detecting a hidden structure without destroying the illuminated environment. They are used in many fields ranging from medical imaging to non-destructive testing through. However, the techniques used so far suffer severe degradation in the quality of measurement and reconstructed images. Usually approximated by a noise, these degradations require to be compensated or corrected by collimating devices and often expensive filtering. These degradation is mainly due to scattering phenomena which may constitute up to 80% of the emitted radiation in biological tissue. In the 80's a new concept has emerged to circumvent this difficulty : the Compton scattering tomography (CST).This new approach proposes to measure the scattered radiation considering energy ranges ( 140-511 keV) where the Compton effect is the phenomenon of leading broadcast. The use of such imaging devices requires a deep understanding of the interactions between radiation and matter to propose a modeling, consistent with the measured data, which is essential to image reconstruction. In conventional imaging systems (which measure the primary radiation) the Radon transformdefined on the straight lines emerged as the natural modeling. But in Compton scattering tomography, the measured information is related to the scattering energy and thus the scattering angle. Thus the circular geometry induced by scattering phenomenon makes the classical Radon transform inadequate.In this context, it becomes necessary to provide such Radon transforms on broader geometric manifolds.The study of the Radon transform on new manifolds of curves becomes necessary to provide theoretical needs for new imaging techniques. Cormack, himself, was the first to extend the properties of the conventional Radon transform of a family of curves of the plane. Thereafter several studies have been done in order to study the Radon transform defined on different varieties of circles, spheres, broken lines ... . In 1994 S.J. Norton proposed the first modality in Compton scattering tomography modeled by a Radon transform on circular arcs, the CART1 here. In 2010, Nguyen and Truong established the inversion formula of a Radon transform on circular arcs, CART2, to model the image formation in a new modality in Compton scattering tomography. The geometry involved in the integration support of new modalities in Compton scattering tomography lead them to demonstrate the invertibility of the Radon transform defined on a family of Cormack-type curves, called C_alpha. They illustrated the inversion procedure in the case of a new transform, the CART3, modeling a new modeling of Compton scattering tomography. Based on the work of Cormack and Truong and Nguyen, we propose to establish several properties of the Radon transform on the family C_alpha especially on C1. We have thus demonstrated two inversion formulae that reconstruct the original image via its circular harmonic decomposition and itscorresponding transform. These formulae are similar to those established by Truong and Nguyen. We finally established the well-known filtered back projection and singular value decomposition in the case alpha = 1. All results established in this study provide practical problems of image reconstruction associated with these new transforms. In particular we were able to establish new inversion methods for transforms CART1,2,3 as well as numerical approaches necessary for the implementation of these transforms. All these results enable to solve problems of image formation and reconstruction related to three Compton scattering tomography modalities.In addition we propose to improve models and algorithms es
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Cooper, Sarah Louise Pamela. "Base excision repair of radiation-induced DNA damage in mammalian cells." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:2c4b3d1e-67c3-4da5-8967-3080b1ebf27a.
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A specific feature of ionising radiation is the formation of clustered DNA damage, where two or more lesions form within one to two helical turns of the DNA induced by a single radiation track. The complexity of ionising radiation-induced DNA damage increases with increasing ionisation density and it has been shown that complex DNA damage has reduced efficiency of repairability. In mammalian cells, base excision repair (BER) is the predominant pathway for the repair of non-DSB clustered DNA lesions and is split into two sub-pathways known as short patch (SP) BER and long patch (LP) BER. SP-BER is the predominant pathway, especially in the repair of isolated DNA lesions. However, LP-BER is thought to play a greater role in the repair of radiation-induced clustered lesions. In this study, cell lines were generated stably expressing the fluorescently tagged BER proteins, XRCC1-YFP (marker for SP-BER) or FEN1-GFP (marker for LP-BER). The recruitment and loss of XRCC1-YFP and FEN1-GFP to sites of DNA damage induced by both ultrasoft X-ray (USX), a form of low linear energy transfer (LET) radiation, and near infrared (NIR) laser microbeam irradiation (‘mimic’ high LET radiation) was visualised in real-time and the decay kinetics of the fluorescently-tagged proteins determined. The half-life of fluorescence decay of FEN1-GFP following USX irradiation was longer than that of XRCC1-YFP, indicating that LP-BER is a slower process than SP-BER. Additionally, the fluorescence decay of XRCC1-YFP after NIR laser microbeam irradiation was fitted by bi-exponential decays with a fast component and a slow component, reflecting the involvement of XRCC1 in the repair of different types of DNA damage. In contrast to USX irradiation, where the XRCC1-YFP fluorescence decay reached background levels by 20 min, XRCC1-YFP still persisted at some of the NIR laser induced DNA damage sites even after 4 hours. This is consistent with the fact that the laser induces more complex damage that presents a major challenge to the repair proteins, persisting for much longer than the simple damage caused by low LET USX irradiation. Persistent, unrepaired DNA damage can potentially lead to mutations and replication-induced DSBs if it persists into S-phase. PARP1 inhibition reduced the recruitment of XRCC1 to DNA damage sites. However, a considerable amount of XRCC1 was still detected at the DNA damage sites, leading to the conclusion that there is a subset of DNA damage that requires XRCC1 but not PARP1 for repair. Understanding how clustered damage is repaired by the BER pathway can aid the design of future therapies which can be used in combination with radiotherapy to enhance the radiosensitisation effect. Knockdown of FEN1 was investigated and found to radiosensitise A549 (adenocarcinoma) cells, possibly as a result of an excess of unrepaired radiation-induced lesions requiring LP-BER for repair, although FEN1 knockdown alone induced cell death in non-cancerous BEAS-2B cells.
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Vedam, Subrahmanya. "Management of Respiratory Motion in Radiation Oncology." VCU Scholars Compass, 2002. http://scholarscompass.vcu.edu/etd_retro/162.
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Respiratory motion poses significant problems in the radiotherapy of tumors located at sites (lung, liver, pancreas, breast) that are affected by such motion. Effects of respiratory motion on the different stages of the radiotherapy process (imaging, treatment planning and treatment delivery), has formed the focus of significant research over the last decade. Results from such research have revealed that respiratory motion affects the instantaneous position of almost all structures in the thorax and abdomen to different degrees based on their corresponding anatomic location and muscular attachments. As an example, diaphragm motion was found to be of the order of 1.5 cm, predominantly in the superior-inferior (SI) direction during normal breathing. This indicates a similar magnitude of motion for tumors located in the lower lobes of the lung and in the abdomen.The conventional method of accounting for such motion is to add a margin (based on an estimate of the expected range of organ motion) around the clinical target volume (CTV) that is delineated from the image data. This margin also includes errors due beam-bony anatomy alignment during radiation delivery and errors in patient position between simulation and subsequent treatment delivery sessions. Such a margin estimate may or may not encompass the "current" extent of motion exhibited by the tumor, resulting in either a higher dose to the surrounding normal tissue or a potential cold spot in the tumor volume. Several clinical studies have reported the existence of a direct relationship between the reduction in mean dose to the lung and the incidence of radiation induced pneumonitis. Therefore, subjecting additional normal lung tissue to high dose radiation by adding large margins based on organ motion estimates may result in an increased risk of radiation induced lung injury.Monitoring and accounting for respiratory motion can however potentate a reduction in the amount of normal tissue that receives high dose radiation, thereby decreasing the probability of normal tissue complication and also increasing the possibility for dose escalation to the actual tumor volume. The management (monitoring and accounting) of respiratory motion during radiation oncology forms the primary theme of this dissertation.Specific aims of this thesis dissertation include (a) identifying the deleterious effects of respiratory motion on conventional radiation therapy techniques (b) examining the different solutions that have been proposed to counter the deleterious effects of respiratory motion during radiotherapy (c) summarizing the relevant work conducted at our institution as part of this thesis in addressing the issue of respiratory motion and (d) visualizing the future direction of research in the management of respiratory motion in radiation oncology.Among the various techniques available to manage respiratory motion in radiation oncology such as respiratory gated and breath hold based radiotherapy, our research initially focused on respiratory gated radiotherapy, employing a commercially available external marker based real time position monitoring system. Multiple session recordings of simultaneous diaphragm motion and external marker motion revealed a consistent linear relationship between the two signals indicating that the external marker motion (along the anterior-posterior (AP) direction) could be used as a "surrogate" for motion of internal anatomy (along the SI direction). The predictability of diaphragm motion based on such external marker motion both within and between treatment sessions was also determined to be of the order of 0.1 cm.Analysis of the parameters that affected the accuracy and efficacy of respiratory gated radiotherapy revealed a direct relationship between the amount of residual motion and the width of the "gate" window. It also followed therefore that a trade-off existed between the width of the "gate" and the accuracy of gated treatments and also the overall "Beam ON" time. Further, gating during exhale was found to be more reproducible than gating during inhale. Although, it was evident that a reduction in the width of the "gate" implied a reduction in the margins added around the clinical target volume (CTV), such a reduction was limited by setup error.A study of the potential gains that could be derived from respiratory gating (based on motion phantom experimental set up) indicated a potential CTV-PTV margin reduction of 0.2-1.1 cm while employing gating alone in combination with an electronic portal imaging device, thus decreasing the amount of healthy tissue receiving radiation. In addition, gating also improved the quality of images obtained during simulation by reducing the amount of motion artifacts that are typically seen during conventional spiral CT imaging.Imparting some form of training was hypothesized to better enable patients to breathe in a reproducible fashion, which was further thought to increase the accuracy and efficacy of gated radiotherapy, especially when the "gate" was set close to the inhale portion of the breathing cycle. An analysis of breathing patterns recorded from five patients over several sessions under conditions of normal quiet breathing, breathing with audio instructions and breathing with visual feedback indicated that training improved the reproducibility of amplitude or frequency of patient breathing cycles.An initial exploration into respiration synchronized radiotherapy was thought to facilitate realization of reduced margins without having to hold the radiation beam delivery during a breathing cycle (as is the case with gating). A feasibility study based on superimposition of respiratory motion of a tumor (simulated by a sinusoidal motion oscillator) onto the initial beam aperture as formed by the multileaf collimator (MLC) revealed that tumor dose measurements obtained with such a set up were equivalent to those delivered to a static tumor by a static beam.Finally, a feasibility study for a method to acquire respiration synchronized images of a motion phantom and a patient (in order to perform respiration synchronized treatment planning and delivery) yielded success in the form of a 4D CT data set with reduced motion artifacts.In summary, respiratory gated radiotherapy and respiration synchronized are both viable approaches to account for respiratory motion during radiotherapy. While respiratory gated radiotherapy has been successfully implemented in some centers, several technical advances are required to enable similar success in the implementation of respiration synchronized radiotherapy. However, the potential clinical gains that can be obtained from either of the above approaches and their relative contributions to margin reduction will determine their future applicability as routine treatment procedures.
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Bakhshwin, Duaa. "Cytoprotective versus Non-protective Autophagy Induced by Radiation in Head and Neck Cancer Cells." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3453.
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The primary treatment options for head and neck cancer are radiation therapy or surgery, or both combined; chemotherapy is often used as an additional, or adjuvant, treatment. Patients treated with radiotherapy are exposed to a high cumulative dose of radiation over a period of time and there is a 17-33% chance of recurrence. High cumulative doses of radiation, a long time course of treatment, side effects and the possibility of recurrence provide the rationale for developing approaches for radiation sensitization, which could be helpful to patients in decreasing the dose, duration of radiation, side effects, or the chance of recurrence. Radiation induces autophagy, which is a catabolic process involving the degradation of the cell’s own components to generate energy under conditions of stress. Autophagy can be cytoprotective helping the cell to survive during stress such as nutrient deprivation or it can be cytotoxic, leading the cell toward death. We investigated whether blocking autophagy by the use of the antimalarial drug, chloroquine, could sensitize head and neck cancer cells to radiation. Studies were performed using the HN30 human head and neck cancer line (p53 wild type) derived from the pharynx as well as HN6 human cells (p53 mutant) derived from the base of the tongue. Cell viability was determined by cell counting and clonogenic survival assays, autophagy was monitored based on acridine orange staining accompanied by flow cytometry, while western blotting, DAPI and TUNEL staining and PI/annexin/FACS were utilized for determination and quantification of apoptosis. Senescence was monitored by beta-galactosidase staining/ FACS analysis. Radiation alone produced a transient growth arrest followed by proliferative recovery in both the HN30 and HN6 cancer cells. Radiation also promoted autophagy in both cell lines. The combination of chloroquine with radiation inhibited autophagy and promoted apoptotic cell death and suppression of proliferative recovery for the HN30 cells, but had little effect on sensitivity to radiation and proliferative recovery in the HN6 cells. The data suggest that autophagy induced by radiation serves a protective function in the HN30 cells and that a blockade to autophagy by chloroquine drives the cell toward apoptosis and death. In contrast, autophagy in HN6 cells appears to be non-protective as a pharmacological blockade did not sensitize the HN6 cells to radiation. These studies support the premise that autophagy induction by radiation need not necessarily have a cytoprotective function and further indicates that caution should be exercised in efforts to sensitize head and neck cancer to radiation through the clinical suppression of autophagy.
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Duchesne, Simon. "An appearance-based method for the segmentation of medial temporal lobe structures from MR images /." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33753.
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A new paradigm for the characterization of structure appearance is proposed, based on a combination of grey-level intensity data and a shape descriptor derived from a priori Principal Components Analysis of 3D deformation vector fields. Generated without external intervention, it extends more classical, 2D manual landmark-based shape models. Application of this novel concept leads to a method for the segmentation of medial temporal lobe structures from brain magnetic resonance images. The strategy employed for segmentation is similar to that used in other appearance-based approaches, while the resulting output data is identical to ANIMAL, a non-linear registration and segmentation technique. The proposed method was tested on a data set of 80 normal subjects for which manual and ANIMAL segmentated structures were available. Experimental results demonstrated the robustness and flexibility of this method. Segmentation accuracy, measured by overlap statistics, is marginally lower (<2%) than ANIMAL, while processing time is 6 times faster. Finally, the applicability of this concept towards shape deformation analysis is presented.
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Sirois, Luc M. "3-D automatic anatomy-based image registration in portal imaging." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0025/MQ50880.pdf.
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Tremblay, Hugo. "La tomographie par émission de positons à l'étude de la réponse hémodynamique temporelle induite par activation cérébrale (TEP-RHETIAC)." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ64469.pdf.
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Suk, Joon Young. "Improving the spatial resolution of the MicroPET R4 scanner by wobbling the bed." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101799.
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The MicroPET R-4 scanner was designed for imaging small rodents such as mice and rats. In many cases its spatial resolution is not good enough to perform the required task. We have implemented an eccentric motion (commonly referred to as wobbling) which is applied to the bed during scanning.The program which histograms the list-mode data was rewritten to increase the spatial sampling by incorporating the wobble position in the sinograms. The corrections for the dwell time, apparent crystal location, and crystal-pair efficiency are applied within the program. A series of scans were performed to decide the optimum wobble radius; it was found to be 1.50 mm. Another series of scans was performed during which a Na-22 source was moved 0.25 mm between scans with and without the optimal wobble motion. The peak-to-valley ratio between two Na-22 point sources 4.0 mm apart, improved from 1.75 in the conventional mode to 2.26 during wobbled scans applying a ramp filter.
The bed wobbling mechanism can he added to the microPET R4 or P4 scanners without any major changes to make wobble motion and without compromising any imaging modes. Implementing the wobble mechanism may present a cost-effective upgrade over a trade in or purchase of the higher performance scanner.
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Asiev, Krum. "Validation of a Monte Carlo based treatment planning system (TPS) for electron beams." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101700.
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A commercial electron dose calculation software (Eclipse TM) implementation based on the Macro Monte Carlo algorithm has been introduced. Eclipse™ initial configurations were performed for all available electron beam energies 6, 9, 12, 16, and 20 MeV. We evaluated the electron Monte Carlo (eMC) module of the Eclipse™ using a verification data set comprised of depth dose curves, profiles, Relative Output Factors (ROF), and 2-0 dose distributions in the transverse plane in a homogeneous phantom. The verification data set was comprised of measurements performed for combinations of 6, 9, 12, 16, and 20 MeV beam energies with five standard field sizes and thirteen irregularly shaped fields under three phantom setups. The phantom setups were normal beam incidence at source-to-surface distance (SSO) = 100cm, normal incidence with extended SSO=11 Ocm, and oblique incidence with extended SSO=11 Ocm. Calculations were performed in a digital phantom with the maximum number of particles accepted by Eclipse ™ with a grid spacing that was no larger than approximately one-tenth the distal falloff distance of the electron depth dose curve from 80% to 20% of the maximum dose. Overall, the agreement between the calculated dose distributions and measured on es was good for fields larger than 2 cm to better than 3% dose difference and 3 mm distance-to-agreement.
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Fraser, Danielle J. "Characterizing ionization chamber dosimetry in inverse planned IMRT fields." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84031.
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It is standard practice in radiation therapy to have two independent calculations for the number of monitor units used in patient treatment plans. The relationship between monitor units and absorbed dose to water is sophisticated for MLC-based IMRT. Verification measurements of absorbed dose to water with ionization chambers in MLC-based IMRT fields remains uncertain and the accuracy of computer modeling is limited by the physics assumptions used. In this thesis, point dose measurements from three cylindrical ionization chambers of different collecting volumes are evaluated against the CORVUS (NOMOS Corporation, Cranberry, PA) finite-size pencil beam algorithm and the PEREGRINE (NOMOS Corporation, Cranberry, PA) Monte Carlo calculation engine. After establishing the characteristics of the chambers and treatment planning system under various beam geometries, dynamic and step and shoot MLC deliveries were evaluated. Between detectors, the smallest volume chamber measured the greatest dose. Compared to measurements, CORVUS and PEREGRINE both underestimated the dose in IMRT fields by approximately 5%. On average PEREGRINE yielded better agreement than CORVUS by 2%.
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Mark, Clarisse Ildikó. "Image-guided radiotherapy using 2D and 3D ultrasound combined with Monte Carlo dose calculations in prostate treatments." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=98761.
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Two ultrasound systems were studied to investigate the effects of positional and volumetric prostate variations on dosimetry over the course of external radiation therapy. A 2D system, currently used at the Montreal General Hospital for patient repositioning, was compared to a 3D system invented recently. Prostate variations were quantified from ultrasound images acquired daily during a 2003 clinical study. A method was devised to introduce ultrasound information in a Monte Carlo Treatment Planning System previously developed at McGill. Patient repositioning was evaluated for both systems using dose-volume histograms of Voxel Monte Carlo dose calculation. Repositioning with the 3D system, neglecting volume changes, was found to bring the target dose to within 1 % of the planned dose, rather than the 12 % of the clinical 2D system. However, when considering the varying 3D volumes, the dose could only be corrected to within 7 %. These results indicate that the 3D system provides not only a more accurate assessment of prostate displacements, but also volumetric information that significantly affects the dosimetry.
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Lemire, Matthieu. "Accurate surface dose measurements in CT examinations using high sensitivity MOSFET dosimeters calibrated by Monte Carlo simulations." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=98747.
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The objective of this work is to use MOSFET dosimeters to accurately measure surface dose delivered during CT examinations in various scanning conditions. To achieve this, the behaviour of MOSFETs under kilovoltage x-ray irradiation first needed to be investigated. A dose-to-dose reproducibility of 4.5%, and a mean change in sensitivity response of 10.4% with accumulated dose were measured. A Monte Carlo model of the x-ray source of a PQ5000 CT simulator was built and validated in order to investigate the MOSFET response characteristics and perform dose calculations. An over-response of 10% was observed when the beam energy was decreased from 140 to 80 kVp, and a slight anisotropy of 8.5% from the mean value over 360º was observed. The dosimeters were calibrated on a solid water phantom using a method involving MC surface dose calculations. Good agreement was found between measurements and simulations of surface dose on a cylindrical PMMA phantom for a stationary tube technique, single axial scan and multiple contiguous axial scans, with generally less than 7.5% discrepancies. Film and MOSFET measurements were then performed for helical adult brain scan parameters using different pitch and collimator settings. The use of five MOSFETs combined in a linear array was found to be suitable to accurately measure surface dose in helical scans for almost all pitch and collimation combinations.
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Alexander, Andrew William. "MMCTP : a radiotherapy research environment for Monte Carlo and patient-specific treatment planning." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101699.
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Accurate dose calculations and analysis tools are essential to radiotherapy treatment planning. Radiotherapy deliveries utilize the information provided by the treatment planning system and it is generally accepted that clinical outcome can be improved if accuracy in the dose delivery is further improved. Proven Monte Carlo calculations increase the planning accuracy however, most radiotherapy departments do not use Monte Carlo. The McGill Monte Carlo treatment planning system, MMCTP, provides a flexible software environment to integrate Monte Carlo planning with current and new treatment modalities and deliveries. The MMCTP design consists of a graphical user interface, which runs on a simple workstation connected through standard secure-shell protocol to a cluster for lengthy Monte Carlo calculations. The impact of this tool lies in the fact that it allows for systematic, platform independent, large-scale Monte Carlo planning calculations for different treatment sites. Various measurements and patient recalculations were preformed to validate the software and ensure proper functionality.
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Reynard, Eric P. "Rotational total skin electron irradiation (RTSEI) with a 6 MeV electron linear accelerator." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101800.
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The rotational total skin electron irradiation technique at the McGill University Health Centre has undergone several developments over the past few years. Replacement of the formerly used linear accelerator has prompted many modifications to the previously reported technique. With the current technique, the patient is treated while standing on a rotating platform, with a single large field at a source to surface distance of 378 cm. The electron field is produced by a Varian 21EX linear accelerator using the commercially developed 6 MeV high dose rate total skin electron mode, along with a custom-built flattening filter. Ionization chambers, radiochromic film, and MOSFET detectors have all been used to confirm the dosimetric properties of this technique. Measurements investigating the stationary beam properties, the effects of full rotation, and the dose distributions to a humanoid phantom are reported. In addition, comparisons with commonly-used stationary beam treatment alternatives are presented.
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Ceusan, Florin. "An examination of peripheral dose in linac-based cancer treatment /." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97921.
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The thesis work contains two related projects. The first project examines the characteristics of the Farmer-type ionization chamber (Farmer-type IC 2571 A) used in our experiments. An investigation was carried out to determine if the simplified "two-voltage technique" used in clinics is sufficiently accurate for saturation current estimation. Three models were used to fit the measured currents and to estimate the saturation current. The estimation was carried out by measuring the currents set-up in the Farmer-type IC while varying the applied voltages, for both polarities, for fixed and variable dose rates. The second project investigated peripheral dose in 6 MV beam using the Farmer-type IC. The signal produced in the ionization chamber when measuring the peripheral dose is 2 to 3 orders of magnitude lower than the signal produced with the chamber in the primary beam, thus, the leakage and saturation characteristics of the ionization chamber had to be investigated to ensure that they do not have adverse effects on the chamber reading. Measurements were acquired in open field (10x10 cm2) and in a dynamic MLC field (10x1 cm2), with the IC at the machine's isocenter.Measurements allowed us to determine peripheral dose due to scatter and leakage radiation. Measurements were repeated for a blocked beam, which allow us to determine only the leakage radiation component of the peripheral dose. The two components of the peripheral dose depend strongly on the linac head configuration and shielding. Leakage radiation per MU for a dMLC field is similar or higher than the leakage radiation for a static field, which implies an increase in peripheral dose for IMRT-type treatments. Knowledge of peripheral dose can be useful in estimating dose and risk to sensitive structures outside of the primary treatment field.
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Duchesne, Caroline. "Electron arc therapy using an Electa SL-25 linear accelerator at Maisonneuve-Rosemont Hospital (Montreal, Canada)." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97944.
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Electron arc therapy is a special radiotherapeutic technique using a rotational electron beam in the treatment of large superficial tumours following curved surfaces. In those cases, arc therapy offers the best way to optimize dose uniformity while sparing healthy tissues and critical organs. The use of this technique overcomes under or over dosage problems caused by field junctions. However, electron arc therapy presents important challenges in terms of dosimetry and treatment planning.Clinical implementation of electron arc therapy requires the study of many parameters of influence such as the radius of curvature of the treated surface, the width of the treatment field, the total angle of irradiation and the beam energy. Monitor unit calculation to deliver prescribed dose is a very critical topic and, in general, requires acquisition of a large amount of measured dosimetric data.
This project concerns the clinical implementation of electron arc therapy using an Elekta SL-25 linear accelerator in the radiation oncology department of the Maisonneuve-Rosemont Hospital (Montreal, Canada). Firstly, the objective of the study is to observe the influence of the radius of curvature, the total arc angle and the field width on the following dosimetric parameters: depth of maximum dose, isodose distributions and electron arc beam output at the depth of maximum dose. Secondly, for our particular setup, the goal is to develop a simple monitor unit calculation method, based on an analytical model fitted through measured dosimetric data covering a large range of possible clinical situations.
In order to achieve these goals, electron arc irradiations were performed on cylindrical acrylic phantoms of different radii, successively varying the total arc angle and the field width at isocentre. Results obtained with thermoluminescent dosimeters show a minor impact of the radius of curvature variation on the percent depth dose curves. However, they show a significant impact on the beam output. It was also observed that the total arc angle influences the dose at the depth of maximum dose only up to a limit angle value, different for each radius of curvature. Finally, the field width at isocentre has an impact on the beam output as well as on the bremsstrahlung contribution at the isocentre.
Concerning the monitor unit calculation, a seven parameter analytical model fitted through measured data was obtained using Origin 7 software. A relationship giving the beam output as a function of the radius of curvature and the total arc angle was found. The field width was not included in the model, but will be part of further investigation before clinical implementation. As future work, dosimetric measurements with other energies should be carried on, mainly to be able to cover a wider range of clinical cases.
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Zakikhani, Ramtin. "Calculated perturbation factors for the NACP-02 plane-parallel ionization chamber irradiated in water by megavoltage electron beams." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99213.
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Measurements of absorbed dose to water in megavoltage electron beams are carried out with cylindrical or plane-parallel ionization chambers. The perturbation factor associated with plane-parallel ionization chambers that have sufficiently large guard rings is assumed to be unity. The NACP-02 chamber is one such chamber that we have investigated in order to determine if this assumption is valid. By performing Monte Carlo simulations with the EGSnrc code, water-to-air Spencer-Attix stopping powers and perturbation factors were calculated in water with a detailed model of the NACP chamber that was validated through results obtained from measurements and simulations. These were determined for electron beam energies between 4 MeV and 19 MeV for a clinical and PSDL linear accelerator. The overall perturbation factor was found to decrease with energy at dref from 1.015 at 4 MeV to 1.004 at 19 MeV and increase with depth for a fixed beam quality.
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Doucet, Robert. "Experimental verification of Monte Carlo calculated dose distributions for clinical electron beams." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33750.
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Current electron beam treatment planning algorithms are inadequate to calculate dose distributions in heterogeneous phantoms. Fast Monte Carlo algorithms are accurate in general but their clinical implementation needs validation. Calculations of electron beam dose distributions performed using the fast Monte Carlo system XVMC and the well-benchmarked general-purpose Monte Carlo code EGSnrc were compared with measurements. Irradiations were performed using the 9 MeV and 15 MeV beams from the Clinac 18 accelerator with standard conditions. Percent depth doses and lateral profiles were measured with thermoluminescent dosimeter and electron diode respectively. The accelerator was modelled using EGS4/BEAM, and using an experiment-based beam model. All measurements were corrected by EGSnrc calculated stopping power ratios. Overall, the agreement between measurement and calculation is excellent. Small remaining discrepancies can be attributed to the non-equivalence between physical and simulated lung material, precision in energy tuning, beam model parameters optimisation and detector fluence perturbation effects.
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St, James Sara. "The effect of changing gamma-ray interaction depth on the "block effect" in PET /." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84076.
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The block effect in Positron Emission Tomography (PET) is the degradation in spatial resolution that is seen when there are more scintillation crystals than photomultiplier tubes in a detector.We measured the block effect in detectors from three PET scanners: the Siemens-CTI HR+, the GE Advance, and the Siemens-CTI HI-REZ. In the CTI HR+ the block effect was 0.7 mm in the central crystals, and negligible for the edge crystals. In the GE Advance the block effect was 0.6 mm for the central crystals, and 0.5 mm for the edge crystals. In the CTI HI-REZ detector the block effect varied from 0.5 mm to 2.1 mm depending on the crystal location.
The effect of changing the depth of the first point of gamma-ray interaction in the block detectors was examined. The gamma-ray interaction depth was varied, and the event position in the crystal identification image was examined. If the events were positioned inconsistently with gamma-ray interaction depth, this might be a cause of the block effect.
In the CTI HR+ detector and the CTI HI-REZ detector, the positioning of events in the crystal identification image was dependent both on the crystal depth of the first point of interaction and the crystal location. In the GE Advance block detector the positioning of events in the crystal identification image was consistent for varying gamma-ray interaction depth, and crystal position.
In crystals where the positioning of events is not consistent with interaction depth, the block effect is larger. In the GE Advance block detector, another cause of the block effect may exist.
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Boudreau, Chantal. "The use of inhomogeneity corrections for inverse planned IMRT /." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81268.
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In this thesis, the use of inhomogeneity corrections in intensity modulated radiotherapy (IMRT) inverse treatment planning is investigated. Firstly, the dosimetric consequences of CT beam hardening artifacts present on images used for treatment planning are estimated and found to be of little clinical significance (<1% dose difference). Secondly, experiments to evaluate the PEREGRINE Monte Carlo system (Nomos, Cranberry, PA) are undertaken for a 6 MV photon beam. The use of inhomogeneity corrections in clinical treatment planning is assessed for five clinical head and neck cancer cases. The cases are planned with the CORVUS optimization module and the dose distributions are then calculated with CORVUS and PEREGRINE in order to compare the two calculation techniques with emphasis on how each method handles tissue inhomogeneities. The plans are assessed in terms of dose, dose-volume distributions and the biological indices of TCP and NTCP. On average, PEREGRINE calculates a 1% lower mean dose to the GTV and a 2% lower mean dose to the CTV compared to the CORVUS calculations with EPL inhomogeneity corrections. In the last part of this work, quality assurance (QA) measurements are performed for a clinical case to investigate how the CORVUS and PEREGRINE calculations agree with the dose measurements on a QA phantom.
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Belanger, Philippe. "MR based frickle-gelatin dosimetry : uncertainty evaluation and computerised analysis of measured dose distributions." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32759.
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Dynamically delivered intensity modulated beams (IMBs) pose unique verification problems that may be addressed with the use of integrating continuous 3D dosimeters such as gel based Fricke dosimeters. Accurate knowledge of the ability of these dosimeters to measure adequately and precisely the delivered dose is a prerequisite for their clinical use. The magnetic properties of the ferrous and ferric ions present in the gel based Fricke dosimeter after its irradiation are the basis for the use of magnetic resonance imaging (MRI) in the measurement of dose. This thesis presents the investigation of a 3D gel based Fricke dosimetry system (Fricke-gel). A software system is developed and spin-lattice relaxation rate (R1) images are computed from MR images of irradiated Fricke-gel phantoms in order to quantify the dosimetric uncertainties resulting from the MR imaging system, from the gel itself, as well as from the external parameters. The sensitivity and the minimum detectable dose of the Fricke-gel dosimeter are determined. Validation of the dosimeter's capacity to measure dose distributions is made through measurement of percent depth dose curves (PDD's), and field profiles (open and wedged). An example of clinical utilisation of the Fricke-gel dosimeter is presented. Dose distributions are evaluated visually by 3D software tools and quantitatively analyzed by dose-volume histograms. Results show a good correlation between the Fricke-gel measured dose distributions and treatment planning software dose calculations.
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Albaret, Claude. "Automated system for Monte Carlo determination of cutout factors of arbitrarily shaped electron beams and experimental verification of Monte Carlo calculated dose distributions." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81259.
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Dose predictions by Monte-Carlo (MC) techniques could alleviate the measurement load required in linac commissioning and clinical radiotherapy practice, where small or irregular electron fields are routinely encountered. In particular, this study focused on the MC calculation of cutout factors for clinical electron beams. A MC model for a Varian linac CL2300C/D was built and validated for all electron energies and applicators. A MC user code for simulation of irregular cutouts was then developed and validated. Supported by a home-developed graphical user interface, it determines in situ cutout factors and depth dose curves for arbitrarily shaped electron fields and collects phase space data. Overall, the agreement between simulations and measurements was excellent for fields larger than 2 cm.The MC model was also used to calculate dose distributions with the fast MC code XVMC in CT images of phantoms of clinical interest. These dose distributions were compared to dose calculations performed by the pencil-beam algorithm-based treatment planning system CadPlan and verified against measurements. Good agreement between calculations and measurements was achieved with both systems for phantoms containing 1-dimensional heterogeneities, provided a minimal quality of the CT images. In phantoms with 3-dimensional heterogeneities however, CadPlan appeared unable to predict the dose accurately, whereas MC provided with a more satisfactory dose distribution, despite some local discrepancies.
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Camborde, Marie-Laure A. "Use of beta-gamma coincidence to improve the quality of transmission scans for PET." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33723.
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The availability of accurately aligned, whole body, functional PET images has a significant impact on the diagnosis of malignant disease and on identifying and localizing metastasis. Gamma ray attenuation correction is essential in all quantitative PET studies.The object of this study was to explore the possibility of using beta-gamma coincidence as an attenuation correction technique in order to improve transmission scan image quality.
This study consisted of testing and implementing a beta-gamma attenuation correction technique on an animal PET scanner. In its final form the system uses 68Ge sources enclosed in plastic scintillator cylinders coupled to PMTs. The detection of positrons is activated by the energy loss in the scintillator medium. This system is used in coincidence with one of the animal PET scanner's BGO crystal detectors in order to acquire transmission scans.
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Huang, Vicky W. "Validation of total skin electron therapy by the Monte Carlo technique." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82253.
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The goal of Total Skin Electron Therapy (TSET) is to deliver a uniform dose to the patient's entire skin to a limited depth while sparing the body organs. Due to the laborious commissioning process, it is helpful to use the Monte Carlo (MC) method for the procedure and treatment planning. Calculations of dosimetric quantities were performed with EGSnrc/BEAM MC codes as well as with the fast MC code XVMC. The linac model for a 6 MeV Varian CL21EX accelerator was established by measuring the electron focal spot size with a slit camera. Using this measured focal spot value in our proposed divergent beam model, an improved result for large field profiles can be achieved. Measured PDDs and profiles under standard set-up and TSET conditions were compared to MC calculations. Overall, satisfactory results were obtained except for simulations with an additional scattering filter, suggesting the composition, density and dimensions of the filter need to be confirmed.
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Watkins, W. Tyler. "Optimization of Radiation Therapy in Time-Dependent Anatomy." VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/3069.
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The objective of this dissertation is to develop treatment planning techniques that have the potential to improve radiation therapy of time-dependent (4D) anatomy. Specifically, this study examines dose estimation, dose evaluation, and decision making in the context of optimizing lung cancer radiation therapy. Two methods of dose estimation are compared in patients with locally advanced and early stage lung cancer: dose computed on a single image (3D-dose) and deformably registered, accumulated dose (or 4D-dose). The results indicate that differences between 3D- and 4D- dose are not significant in organs at risk (OARs), however, 4D-dose to a moving lung cancer target can deviate from 3D-dose. These differences imply that optimization of the 4D-dose through multiple-anatomy optimization (MAO) can improve radiation therapy in 4D-anatomy. MAO incorporates time-dependent target and OAR geometry while enabling a simple, clinically realizable delivery. MAO has the potential to enhance the therapeutic ratio in terms of target coverage and OAR sparing in 4D-anatomy. In dose evaluation within 4D-anatomy; dose-to-mass is a more intuitive and precise metric in estimating the effects of radiation in tissues. Assuming physical density is proportional to functional tissue density, dose-to-mass has a 1-1 correspondence with radiation damage. Dose-to-mass optimization boosts dose in massive regions of lung cancer targets and can reduce integral dose to lung by preferentially treating through regions of low-density lung tissue. Finally, multi-criteria optimization (MCO) is implemented in order to clarify decision making during plan design for lung cancer treatment. An MCO basis set establishes a patient-specific decision space which reveals trade-offs in OAR-dose at a fixed, constrained target dose. By interpolating the MCO basis set and evaluating the plan on 4D-anatomy, patient- and organ- specific conservatism in plan design can be expressed in real time. Through improved methods of dose estimation, dose evaluation, and decision making, this dissertation will positively impact radiation therapy of time-dependent anatomy.
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Le, Jade. "THE ROLE OF CYTOPROTECTIVE AND NON-PROTECTIVE AUTOPHAGY IN RADIATION SENSITIVITY IN BREAST TUMOR CELLS." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3425.
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In general, ionizing radiation promotes cytoprotective autophagy in a majority of breast tumor cells. Previous studies from our laboratory indicated that radiation (5x2 Gy) induces cytoprotective autophagy in MCF-7 cells. In the current work, inhibition of autophagy by silencing of Beclin-1 in MCF-7 cells resulted in an increase in sensitivity to radiation based both on cell number and clonogenic survival; however, there was no increase in apoptosis and the basis for this sensitization is currently under investigation. Unexpectedly, enhancement of autophagy by silencing of Bcl-2 also led to an increase in sensitivity to radiation, possibly through the conversion of cytoprotective to cytostatic autophagy. In contrast to the MCF-7 cells, radiation (5x2 Gy) induces non-protective autophagy in Hs578t cells. Interference with autophagy through silencing of Beclin-1 or induction of Bcl-2 did not alter radiation sensitivity in the Hs578t cells. Since the induction of cytoprotective autophagy can represent an impediment to radiation therapy, it is important to understand the types of autophagy that occur in response to radiation in specific cellular settings and whether interference with autophagy can increase sensitivity to different forms of cancer treatment.