/library/oar/handle/123456789/12848 2026-08-15T18:50:44Z /library/oar/handle/123456789/13664 Title: Adapting planning strategies for cervix brachytherapy to reduce the dose to the vagina Abstract: Background: The implementation of Image-guided Brachytherapy (IGBT) to treat cervical cancer has improved delineation of the target structures and Organs At Risk (OARs) to provide a more conformal and individualised treatment for patients. A European study on MRI guided brachytherapy in locally advanced cervical cancer (EMBRACE) is assessing the impact of IGBT in a multi-institutional setting. Findings of the EMBRACE study demonstrate that vaginal morbidity is common and may e ect the patients' Quality Of Life (QOL). Vaginal dose parameters still need to be de ned; only few studies have looked at this in detail. Objectives: To recommend the most appropriate planning strategy for IGBT of the cervix that conforms to all current planning aims and provides the greatest vaginal dose sparing. Research Design: Fifteen patients that were previously treated for cervical carcinoma with a Computed Tomography (CT)/Magnetic Resonance Imaging (MRI) compatible tandem-ring applicator were chosen. Five patients were randomly selected from the aforementioned sample. Di erent methods were investigated on these ve patients to model appropriately the dose to the vagina. These methods include vaginal points and volumetric dose parameters. Di erent planning strategies such as the clinically delivered plan, standard Manchester plan, conformal plan with modi ed applicator dwell time and positions and the Inverse Planning Simulated Annealing (IPSA) algorithm were applied on the ve patients and the best treatment plan in reducing the dose to the vaginal wall was applied to the rest of patients. The best vaginal dose reporting method and planning strategy were implemented for the rest of the patients and the resulting dose parameters were compared to the ones resulting from the clinically delivered plan. Finally, an investigation was done to determine whether vaginal morbidity including mucositis, stenosis, dryness and bleeding can be correlated with vaginal dose. Results and Conclusions: From this study it was concluded that the vaginal Dose Volume Histogram (DVH) parameters for the vaginal wall are inaccurate due to contouring uncertainties. On the other hand the vaginal dose points presented in this study provide a good dose representation throughout the vagina and can easily be used clinically in the near future. The best planning strategy in reducing the vaginal dose whilst maintaining the current planning aims was found to be the manual conformal plan. It kept the target coverage and dose to the bladder, rectum sigmoid and small bowel within dose constraints while it reduced vaginal dose by 42.34 %, 30.28 %, 33.71 %, 28.00 % and 24.21 % at the vaginal ring surface, the transition zone between middle and upper vagina, the anatomical mid-vagina, the transition zone from the lower and middle part of vagina and the vaginal introitus respectively. No correlation could be demonstrated between brachytherapy vaginal dose and vaginal morbidity in this small sample of patients used in this study. Description: M.SC.MEDICAL PHYSICS 2015-01-01T00:00:00Z /library/oar/handle/123456789/13380 Title: A comparison of SNR of two generations of Siemens 1.5T MRI scanners and their associated RF phased array coils Abstract: Background: The hospital where this study was carried out is in possession of two whole-body MRI Siemens scanners (Siemens Magnetom Aera (2012) and Siemens Magnetom Avanto (2007), Erlangen, Germany). Both machines have field strength of 1.5T but have significant differences between them, namely: the bore size, field of view restrictions and radio frequency receive coils. Despite these differences, the two machines are currently being operated using the same protocol which indicates that the latter may not be optimised for both scanners. Objectives: The primary purpose of this study was to measure and compare Signal to noise ratio (SNR) and SNR uniformity of the two systems. A second objective was to evaluate the different methods of SNR measurement found in MRI literature. Research Design: SNR measurements were carried on spin echo (SE) images using the head coils and combination of body-spine coils. SNR evaluation was carried out on region-of-interests (ROIs) on both phantom and anonymised patient images. The American College of Radiology (ACR) phantom and five cylindrical fluid filled phantoms provided by the manufacturer were used to obtain phantom images. For patient images, neurological and prostate images were used for evaluation of SNR. Different approaches of SNR measurement were compared in phantom measurements with the gold standard multiple-acquisition method (MAM). In patient images only single-image methods could be applied. Results: Deviations from the gold standard were noted. For the head phantom measurements, the Aera produced higher SNR than the Avanto with the highest being 166% and lowest 131%. For the body phantom, SNR values from the Aera were again higher, the highest being 132% and lowest 103%. In general, t-testing indicated that the Aera produces significantly (P<0.05) higher SNR than the Avanto for various ROIs on patient images. Conclusions and recommendations: The Aera scanner produced higher SNR than the Avanto for both phantom and patient images. Based on the assumption that the Avanto SNR is adequate, it is recommended that the increased SNR of the Aera should be used to optimise scanning protocols allowing shorter scan times or improvements in resolution. Description: M.SC.MEDICAL PHYSICS 2015-01-01T00:00:00Z /library/oar/handle/123456789/13317 Title: Paediatric CT protocol optimisation of the abdo-pelvic region Abstract: Background: Local radiologists had expressed concerns regarding patient dose and image quality for paediatric abdomen-pelvis scans on a GE VCT scanner relative to a Siemens Definition system. Objective: To improve the image quality of a GE Lightspeed VCT scanner relative to the Siemens Definition scanner, whilst keeping the radiation dose to a minimum for paediatric abdomen-pelvis scans. Research Design: Dose and image quality measurements were collected for the full range of weight-based protocols on both scanners using a 32cm CTDI phantom and Catphan 500 image quality phantom. For dose measurements on both scanners axial protocols were created. For image quality, the GE scanner has the iterative reconstruction option (ASIR) available. Results: The radiation dose from the GE scanner was originally higher than from the Siemens scanner prior to optimisation especially for patients weighing between 22.5 - 55 kg with percentage differences ranging from 50% - 96.2%. These doses were reduced by 34 - 50% post optimisation to fall within 21.65% of the Siemens doses. Before any optimisation was done the noise on the GE scanner was between 39% greater to 26% lower than the Siemens scanner and post optimisation the same noise was reduced to 7% greater and 8% lower than the noise on the Siemens system with an increased overall performance of ~ 9%. With Adaptive Statistical Iterative Reconstruction (ASIR) there were dose savings of 34.7% - 50.5% for the 22.5 - 55 kg patients and a noise reduction of ~ 6 - 8% with the same percentage increase for the CNR. Conclusion: The GE Lightspeed VCT scanner achieved broadly similar image quality (noise and contrast-to-noise ratio (CNR)) and better overall performance (figure-of-merit (FOM)) at reduced or similar radiation doses as the Siemens Definition scanner (reference scanner). Recommendations: Adequate training and education about paediatric doses must be provided to radiologists and operators. Another recommendation would be implementing the changes in the GE protocols. Finally, a change in the clinical workflow might also be beneficial to efficiently use both scanners. Description: M.SC.MEDICAL PHYSICS 2015-01-01T00:00:00Z /library/oar/handle/123456789/13018 Title: Noise power spectrum of ultrasound uniformity images Abstract: Background: The Noise Power Spectrum (NPS) is an effective tool for providing information on how the total noise variance of uniformity images is distributed in frequency space. The NPS is a tool which can widen the understanding of noise in ultrasound as noise in ultrasound includes both electronic stochastic noise and static speckle. However, surprisingly very little research has been done and unlike projection XRI and CT, NPS is not included in QC protocols for ultrasound. Objectives: (1) To establish a scan protocol to obtain the NPS for ultrasound scanners and linear transducers (2) To specify an IQWorks analysis tree for the calculation of All Noise, Stochastic and Static NPS for ROIs at near field, focal region and far field (3) To investigate the variation of NPS with output power over the three regions (4) To investigate the short term reliability of the methodology. Research Design: The protocol was developed on a Siemens ACUSON Sequoiaâ„¢ and two phantoms (Gammex RMI404GS LE, CIRS Model 551). ImageJ and IQWorks were used to calculate the NPS at the near field, focal region and far field. The reliability of the methodology was checked by calculating the coefficient of variation (CoV) of the mean pixel value (MPV), image variance and NPS over repeat acquisitions. Results: The NPS of ultrasound systems includes a high low-frequency component arising from the speckle. The far field region experienced the highest stochastic and static NPS values as the output power decreased. There was a sudden increase in the stochastic NPS at the focal region for both phantoms when the phantom decreased from -4dB to -7dB. CoVs for both phantoms were generally less than 8%. Conclusion: Noise in ultrasound is mainly of low-frequency component. There are interesting changes of the NPS at different depths and as the output power is reduced. Recommendations: The NPS tool can be used as part of an ultrasound QC programme using the NPS analysis tree specified in this project. Description: M.SC.MEDICAL PHYSICS 2015-01-01T00:00:00Z