Room: Exhibit Hall | Forum 3
Purpose: A real-time tumor-tracking radiotherapy (RTRT) system, SyncTraX FX4 (Shimadzu Co.), which combined with a TrueBeam accelerator (Varian Medical Systems), was installed in our institution for the first time in the world. For novel RTRT technique with kV-MV simultaneous irradiation, it is concerned about the reduction of the accuracy for RTRT by the influence of contaminant MV-scatter. The purpose of this study was to evaluate the accuracy of RTRT with kV-MV simultaneous irradiation with high-dose rate FFF beam before clinical application.
Methods: We assessed the tracking and recognition accuracies of the gold markers in the condition of circular motion at 20, 40, and 60 mm/s with an in-house phantom during fluoroscopy using the SyncTraX FX4 system. A tracking error (TE) and pattern recognition score (PRS) were analyzed by log files acquired in each situation: (1) only fluoroscopic kV beam (MVoff mode), (2) fluoroscopic kV plus 10 MV FFF beams at 10x10 cmÂ² with 2400 MU/min (MVon mode). TE was evaluated by the root mean square (RMS) of the discrepancy between the actual and measured positions of each marker.
Results: The values of RMS were 0.37 mm for MVoff mode and 0.45 mm for MVon mode at 20 mm/s, 0.43 mm and 0.54 mm at 40 mm/s, 0.45 mm and 0.60 mm at 60 mm/s. The relative differences of PRS between MVoff and MVon modes were 0.071Â±0.014 at 20 mm/s, 0.022Â±0.28 at 40 mm/s, and 0.11Â±0.12 at 60 mm/s.
Conclusion: Our results show that the contaminant MV-scatter with 10 MV FFF beam has little influence on the recognition and tracking accuracies of the gold markers. It could be achieved with good accuracy for novel RTRT with kV-MV simultaneous irradiation with high-dose rate FFF beam.