Cone beam computerized tomography: the effect of Hounsfield unit number of image quality

Full text: The use of Cone Beam Computed Tomography (CBCT) integrated with Linear accelerator is increasingly popular in improving patient's position verification. This has led to investigating the feasibility of using CBCT potentially in place of a planning CT (PCT) for treatment planning. Since there is no clinically approved protocol so far, an effective approach to develop Varian kV CBCT onboard imager as a clinically efficient tool for treatment planning is taken. Uniform, reproducible and reliable Hounsfield Unit (HU) in CBCT should be considered in order to improve the image quality for dose calculations. Density phantoms, water and catphan phantoms were scanned by Varian kV CBCT and by Philips big bore brilliance PCT under similar conditions and the line profiles were extracted using Image J software. The HU values and profiles of images acquired were compared to those in PCT. The homogeneous phantom showed reduced HU values up to 100 HU ± 2. The catphanline profiles in CBCT although found to be in agreement with PCT, it is noisier compared to PCT, shown in Fig, I and maximum HU difference was 75HU in Teflon (peak region). h artefacts in CBCT become severe surrounding high-density materials in density phantoms with reduced HU values up to 420. CBCT images are more prone to artefacts like ring an crescent-shaped due to beam scattering and KV tube misalignment . Further works are required to improve the image quality by developing a filter, followed by mapping CBCT HU values with PCT.