Development of image quality assurance measures of the ExacTrac localization system using commercially available image evaluation software and hardware for image‐guided radiotherapy

Quality assurance (QA) of the image quality for image-guided localization systems is crucial to ensure accurate visualization and localization of target volumes. In this study, a methodology was developed to assess and evaluate the constancy of the high-contrast spatial resolution, dose, energy, contrast, and geometrical accuracy of the BrainLAB ExacTrac system. An in-house fixation device was constructed to hold the QCkV-1 phantom firmly and reproducibly against the face of the flat panel detectors. Two image sets per detector were acquired using ExacTrac preset console settings over a period of three months. The image sets were analyzed in PIPSpro and the following metrics were recorded: high-contrast spatial resolution (f30, f40, f50 (lp/mm)), noise, and contrast-to-noise ratio. Geometrical image accu- racy was evaluated by assessing the length between to predetermined points of the QCkV-1 phantom. Dose and kVp were recorded using the Unfors RaySafe Xi R/F Detector. The kVp and dose were evaluated for the following: Cranial Standard (CS) (80 kV,80 mA,80 ms), Thorax Standard (TS) (120 kV,160 mA,160 ms), Abdomen Standard (AS) (120 kV,160 mA,130 ms), and Pelvis Standard (PS) (120 kV,160 mA,160 ms). With regard to high-contrast spatial resolution, the mean values of the f30 (lp/mm), f40 (lp/mm) and f50 (lp/mm) for the left detector were 1.39 ± 0.04, 1.24 ± 0.05, and 1.09 ± 0.04, respectively, while for the right detector they were 1.38 ± 0.04, 1.22 ± 0.05, and 1.09 ± 0.05, respectively. Mean CNRs for the left and right detectors were 148 ± 3 and 143 ± 4, respectively. For geometrical accuracy, both detectors had a measured image length of the QCkV-1 of 57.9 ± 0.5 mm. The left detector showed dose measurements of 20.4 ± 0.2 μGy (CS), 191.8 ± 0.7 μGy (TS), 154.2 ± 0.7 μGy (AS), and 192.2 ± 0.6 μGy (PS), while the right detector showed 20.3 ± 0.3 μGy (CS), 189.7 ± 0.8 μGy (TS), 151.0 ± 0.7 μGy (AS), and 189.7 ± 0.8 μGy (PS), respectively. For X-ray energy, the left detector (right X-ray tube) had mean kVp readings of 81.6 ± 0.5 (CS), 122.5 ± 0.5 (TS), 122.0 ± 0.8 (AS), and 122.1 ± 0.7 (PS), and the right detector (left X-ray tube) had 81.6 ± 0.5 (CS), 120.8 ± 0.5 (TS), 120.9 ± 0.6 (AS), and 121.3 ± 0.7 (PS). Run charts were created so that each parameter could be tracked over time and the constancy of the system could be monitored. A methodology was developed to assess the basic image quality parameters recommended by TG-142 for the ExacTrac system. The ExacTrac system shows a consistent dose, kVp, high-contrast spatial resolution, CNR, and geometrical accuracy for each detector over the evaluated timeframe.