Room: Exhibit Hall | Forum 6
Purpose: Orthogonal radiographic imaging (ExacTrac, Brainlab) has been the standard for intra-fraction alignment of linear accelerator based stereotactic radiosurgery (SRS) patients. Surface imaging (AlignRT, VisionRT) offers the possibility of real time monitoring and alignment without ionizing radiation.
Methods: A head phantom with a real human skull and fiducial markers was positioned on a Varian TrueBeam in a custom jig that allowed for ExacTrac, AlignRT, and orthogonal MV/KV pairs from the TrueBeam to be acquired at table angles 0Â°, +/-45Â°, +/-90Â° without the need to move the gantry. The phantom was initially aligned with ExacTrac, then a new AlignRT reference surface was acquired. Images from all three systems were acquired at each table angle. Movement from the initial position was determined for all imaging systems (the fiducial markers were check movement from the TrueBeam radiographic isocenter). This was repeated for 6 isocenter positions (anterior-most, posterior-most, center, inferior-most, posterior-most, left-most in the skull) over 3 head tilts (chin-up, chin-neutral, chin-down).
Results: The magnitude of translations between the TrueBeam determined position and the other systems over all phantom orientations were 0.7 +/-0.3 (0.2-1.4) for AlignRT-TrueBeam, 0.7 +/-0.3 (0.3-1.4) for ExacTrac-TrueBeam, and 0.4 +/-0.2 (0.1-1.0) for AlignRT-TrueBeam (+/- 1 SD with range). The results showed negligible difference when separated by head tilt or isocenter. The largest differences were seen at table = 90Â°: 1.1 +/-0.2 (0.7-1.4) for AlignRT-TrueBeam, 1.0 +/-0.2 (0.5-1.3) for ExacTrac-TrueBeam, 0.4 +/-0.2 (0.1-0.8) for AlignRT-TrueBeam; and table = -90Â°: 0.8 +/-0.3 (0.2-1.3) for AlignRT-TrueBeam, 0.9 +/-0.2 (0.3-1.4) for ExacTrac-TrueBeam, and 0.4 +/-0.2 (0.1-0.9) for AlignRT-TrueBeam.
Conclusion: ExacTrac and AlignRT showed similar behavior in phantom, both exhibiting accuracy on the order of 1 mm at all table angles. Based on phantom data alone, AlignRT is a comparable alternative to ExacTrac for SRS intra-fraction alignment.
Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by VisionRT