Assessment of the variation in CT scanner performance (image quality and Hounsfield units) with scan parameters,for image optimisation in radiotherapy treatment planning |
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| Affiliation: | 1. Department of Physics, Faculty of Engineering and Physical Science, University of Surrey, Guildford, UK;2. Department of Medical Physics, Portsmouth Hospitals NHS Trust, Portsmouth, UK;3. Department of Medical Physics, Royal Surrey County Hospital NHS Foundation Trust, Guildford, UK;1. School of Dentistry and Medical Sciences, Faculty of Science and Health, Charles Sturt University, Wagga Wagga, NSW 2650, Australia;2. Department of Medical Imaging, Faculty of Applied Health Sciences, The Hashemite University, Zarqa 13133, Jordan;3. School of Health Sciences, Faculty of Health, University of Canberra, Canberra, ACT 2601, Australia;1. Department of Radiology, Mayo Clinic, Rochester, Minnesota;2. Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas;3. Department of Radiology, Mayo Clinic, Jacksonville, Florida;1. Inselspital – Bern University Hospital, University Institute of Diagnostic, Interventional, and Pediatric Radiology, Freiburgstrasse 10, 3010 Bern, Switzerland;2. Roentgeninstitut Duesseldorf, Kaiserswerterstrasse 89, 40476 Duesseldorf, Germany;3. University Medical Center Hamburg Eppendorf, Department of Diagnostic and Interventional Radiology, Martinistrasse 52, 20246 Hamburg, Germany;4. University of Würzburg, Insitute of Diagnostic and Interventional Radiology, Oberdürrbacher Str. 6, 97080 Würzburg, Germany;1. Unitat de Física Mèdica, Universitat Rovira i Virgili (URV), Spain;2. Radiology Department, Leiden University Medical Center (LUMC), The Netherlands;3. Departamento de Radiología, Universidad Complutense de Madrid (UCM), Spain;1. Department of Radiation Oncology, University Hospital, LMU Munich, D-81377 Munich, Germany;2. Department of Experimental Physics – Medical Physics, LMU Munich, D-85748 Munich, Germany;3. German Cancer Consortium (DKTK), Munich, Germany;4. Comprehensive Pneumology Center Munich (CPC-M), Member of the German Center for Lung Research (DZL), Germany |
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| Abstract: | PurposeTo define a method and investigate how the adjustment of scan parameters affected the image quality and Hounsfield units (HUs) on a CT scanner used for radiotherapy treatment planning. A lack of similar investigations in the literature may be a contributing factor in the apparent reluctance to optimise radiotherapy CT protocols.MethodA Catphan phantom was used to assess how image quality on a Toshiba Aquilion LB scanner changed with scan parameters. Acquisition and reconstruction field-of-view (FOV), collimation, image slice thickness, effective mAs per rotation and reconstruction algorithm were varied. Changes were assessed for HUs of different materials, high contrast spatial resolution (HCSR), contrast-noise ratio (CNR), HU uniformity, scan direction low contrast and CT dose-index.ResultsCNR and HCSR varied most with reconstruction algorithm, reconstruction FOV and effective mAs. Collimation, but not image slice width, had a significant effect on CT dose-index with narrower collimation giving higher doses. Dose increased with effective mAs. Highest HU differences were seen when changing reconstruction algorithm: 56 HU for densities close to water and 117 HU for bone-like materials. Acquisition FOV affected the HUs but reconstruction FOV and effective mAs did not.ConclusionsAll the scan parameters investigated affected the image quality metrics. Reconstruction algorithm, reconstruction FOV, collimation and effective mAs were most important. Reconstruction algorithm and acquisition FOV had significant effect on HU. The methodology is applicable to radiotherapy CT scanners when investigating image quality optimisation, prior to assessing the impact of scan protocol changes on clinical CT images and treatment plans. |
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| Keywords: | Radiotherapy CT Imaging Optimisation |
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