Effect of image quality on correlation modeling error using a fiducial marker in a gimbaled linear accelerator.

The purpose of this study was to investigate the effect of image quality under various imaging parameters (60, 70, 80, 90, 100, 110, and 120 kV at 200 mA and 10 ms/63, 80, 100, 160, 200, 250, and 320 mA at 120 kV and 10 ms) and the diameter of the fiducial marker (0.25, 0.50, 0.75, and 1.10 mm) on the correlation modeling error for dynamic tumor tracking (DTT) in the Vero4DRT system. Each fiducial marker was inserted into the center of the 30 × 30 × 10 cm3 water-equivalent phantom. A programmable respiratory motion table was used to simulate breathing-induced organ motion, with an amplitude of ±20 mm and a breathing cycle of 4 s. The correlation modeling error was calculated from the absolute difference between the detected and predicted target positions in the cranio-caudal direction. The image contrast of the fiducial marker was enhanced with increasing kV and mA. Increasing the diameter of the fiducial marker also enhanced the image contrast. Correlation-modeling error does not depend on the image quality and fiducial marker diameter. A lower kV setting did not generate a 4D model due to poor image contrast. All fiducial marker diameters were identified as good candidates for DTT in the Vero4DRT system.