The impact of the ClearRT(™) upgrade on target motion tracking accuracy in Radixact(®) Synchrony(®) lung treatments

BACKGROUND: The objective was to investigate the change in segmentation error of Radixact(®) Synchrony(®) lung treatment after its kV imaging system was upgraded from Generation 1 to Generation 2 in the ClearRT™ installation. MATERIALS AND METHODS: Radixact(®) Lung Synchrony(®) plans were created for the Model 18023 Xsight(®) Lung Tracking “XLT” Phantom combined with different lung target inserts with densities of 0.280, 0.500, 0.943 and 1.093 g/cc. After Radixact(®) Synchrony(®) treatment delivery using the Generation 1 and Generation 2 kV systems according to each plan, the tracking performance of the two kV systems on each density insert was compared by calculating the root mean square (RMS) error (δ(RMS)) between the Synchrony-predicted motion in the log file and the known phantom motion and by calculating δ95%, the maximum error within a 95% probability threshold. RESULTS: The δ(RMS) and δ95% of Radixact(®) Synchrony(®) treatment for Gen1 kV systems deteriorated as the density of the target insert decreased, from 1.673 ± 0.064 mm and 3.049 ± 0.089 mm, respectively, for the 1.093 g/cc insert to 8.355 ± 5.873 mm and 15.297 ± 10.470 mm, respectively, for the 0.280 g/cc insert. In contrast, no such trend was observed in the δ(RMS) or δ95% of Synchrony(®) treatment using the Gen2 kV system. The δ(RMS) and δ95%, respectively, fluctuated slightly from 1.586 to 1.687 mm and from 2.874 to 2.971 mm when different target inserts were tracked by the Gen2 kV system. CONCLUSION: With improved image contrast in kV radiographs, the Gen2 kV imaging system can enhance the ability to track targets accurately in Radixact(®) Lung Synchrony(®) treatment and reduce the segmentation error. Our study showed that lung targets with density values as low as 0.280 cc/g could be tracked correctly in Synchrony treatment with the Gen2 kV imaging system.