The impact of the variation of parameters on image quality and patient dose from computed tomography simulator
Keywords:
Computed Tomography Simulator, Image Quality, Volume Weighted Computed Tomography Dose IndexAbstract
Background: Radiographic images from computed tomography simulator (CT sim) used in radiotherapy should have sufficient quality to be used for cancer treatment planning while the radiation received by the patients should be kept as low as possible. Image quality had an impact on the ability to identify locations of tumor and organs at risk, therefore poor image quality may result in tumor mislocalization and also the efficiency of cancer treatment.
Objective: This study aimed to examine the impact of variation of parameters such as tube voltage, tube current, field of view (FOV) on image quality and patient radiation dose according to the standard criteria of image quality recommended by the American Association of Physicists in Medicine (AAPM) TG 66 to be used as a guideline for radiotherapy.
Materials and Methods: The CATPHAN phantom was scanned by using 36 different CT sim protocols, of which the scanning parameters were changed (80 - 135 kV, 100 - 300 mA and 400 - 700 mm FOV). Quantitative image qualities in terms of the spatial resolution, uniformity, and contrast to noise ratio (CNR) obtained from individual scans were assessed using the RIT software version 6.8.64. Values of volume computed tomography dose index (CTDIvol) were recorded.
Results: The larger FOV, higher tube current and tube voltage resulted in higher CTDIvol. There were five protocols that passed the standard criteria of image quality. These were from the tube voltage settings of 120 kV and 135 kV, tube current settings of 200 mA and 300 mA and FOV setting of 400 mm; as well as tube voltage setting of 135 kV, tube current setting of 300 mA and FOV setting of 550 mm.
Conclusion: Tube voltage, tube current and FOV had an impact on the image quality and patient radiation dose. The protocol recommended by the researcher is the tube voltage setting of 120 kV, tube current setting of 200 mA and FOV setting of 400 mm.
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