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

Ruijie Rachel Liu,Michael Gillin,Karl Prado

doi:10.1120/jacmp.v10i3.2844

Ruijie Rachel Liu, Michael Gillin + Show 1 more

Open Access

https://doi.org/10.1120/jacmp.v10i3.2844

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Abstract

For most computed tomography (CT) simulators, radiation therapists must first remove the fat 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 fat 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 couch top changed the uniformity of water's CT number slightly, but did not change the visual image resolution. The couch top also produced different, yet reproducible, effects on image quality. The effects were greatest in the section of the phantom closest to the couch top. For a commercial carbon fiber couch top, the variation was within 3 Hounsfield Units (HU). The effect was couch‐ and scanner‐specific, and could be incorporated into the QA acceptability criteria for each CT scanner. By using the proposed QA program and phantom, we have been able to implement more thorough QA while decreasing the amount of effort and time the simulation therapists spend performing laser and imaging QA.PACS number(s): 87.55.Gh, 87.55.Qr, 87.56.Fc, 87.57.Q‐

Highlights

50 Liu et al.: On-couch quality assurance (QA) for computed tomography (CT) simulators is heavy, switching couches wastes time and effort, but may cause accidents or damage to the facility.To avoid removing the flat couch to perform CT QA and to simplify the daily QA procedure while performing more thorough QA, we designed a simple yet comprehensive daily QA program and phantom for CT simulators that encompasses both laser and imaging QA
We evaluated high-contrast resolution (Fig. 3(a)) and low-contrast resolution (Fig. 3(b)) for GE scanners, and found that they were, within the sensitivity of the phantom, equivalent to phantom in-air QA as performed with unmodified phantoms attached to the couch end
Because of its increased attenuation, the foot extension, which was placed on the flat couch top, caused larger variation in CT number in the GE LS RT 16 scanner

Summary

Introduction

50 Liu et al.: On-couch QA for CT simulators is heavy, switching couches wastes time and effort, but may cause accidents or damage to the facility. To avoid removing the flat couch to perform CT QA and to simplify the daily QA procedure while performing more thorough QA, we designed a simple yet comprehensive daily QA program and phantom for CT simulators that encompasses both laser and imaging QA. While conventional imaging QA uses “phantom in-air” CT imaging, our new procedure scans the couch and the phantom concurrently. We needed to evaluate the couch’s effect on image quality and incorporate it into the QA criteria. The purpose of this study was to demonstrate the feasibility of this CT QA method

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