Simplified “on-couch ” daily quality assurance procedure for CT simulators

For most computed tomography (CT) simulators, radiation therapists must first remove the flat couch top in order to perform daily CT quality assurance (QA), and then use separate tools to perform localization-laser QA. This process wastes time and effort, and creates the opportunity for accidents to occur. In this study, we tested a simple, yet comprehensive, daily QA program and phantom designed for CT simulators used in radiation oncology that would enable us to use only one tool to perform both laser and imaging QA on a flat couch. To construct a modified QA phantom, we attached three adjustable legs and fastened two metric scales (one vertically and one horizontally) to a commercial CT QA phantom. The adjustable legs helped to position and level the phantom conveniently in the needed position. The two metric scales were used for localization-laser QA, while the phantom body was used for CT imaging QA. We evaluated five different CT scanners from two manufacturers with their designated couches to evaluate this phantom system. Since the couch is scanned along with the phantom, we evaluated the couch’s effect on image quality. We found that the presence of the couc

Optimal acquisition parameter selection for CT simulators in radiation oncology

The purpose of this study was to identify optimal CT acquisition parameter settings for each make and model of scanners used in a large Radiation Oncology (RO) Department, considering the special requirements of CT simulation. Two CT phantoms were used to evaluate the image quality of the five different multichannel CT scanners using helical scan mode. We compared the effects of various pitch, detector configurations, and rotation time parameters on image artifacts, and on spatial and contrast resolution. We found that helical artifact was closely related to pitch and detector configuration settings. This artifact was scannerspecific and generally more obvious when the channel width or detector collimation was equal to the image thickness. Different acquisition parameter settings produced slight differences in observed high- and low-contrast resolution. Short rotation time degraded image quality for certain scanners, but only slightly, while other rotation times, such as 0.75 sec/rotation and above, had no obvious effect on resolution. An optimized combination of acquisition parameters was determined for each scanner make and model, based on phantom image quality and other considerations for clinical applications. This information may be directly useful for physicists whose CT simulation scanners match one of the five examined in this study. If not, the strategy reported here may be used as a guide to perform a similar evaluation of the scanner