Room: Karl Dean Ballroom B1
Purpose: We present the first method for 6DoF motion monitoring using intermittent 2D kV imaging and continuous external respiratory signal.
Methods: Our approach is to optimise a state-augmented linear correlation model between external signal and internal 6DoF motion. In standard treatments, the model can be built using information obtained during pre-treatment CBCT. Real-time 6DoF tumor motion can then be estimated using just external signal. Intermittent intrafraction kV images are used to update the model parameters, accounting for changes in correlation and baseline shifts. The method was evaluated in silico using data from 6 lung SABR patients, with recorded electromagnetic Calypso beacons for internal tumors motion together with external signal from a bellow belt. 2D images from CBCT (10Hz) and intermittent kV images were simulated by projecting the 3D Calypso beacon positions onto an imager. IMRT and VMAT treatments were simulated with increasing imaging update intervals: 0.1s, 1s, 3s, 10s and 30s. The ground-truth dataset contained motion of 0.6Â±3.6mm, -1.2Â±5.5mm and -0.9Â±5.1mm in the Left-Right (LR), Superior-Inferior (SI) and Anterior-Posterior (AP) directions, respectively, and, -0.5Â±3.0Â°, 1.6Â±3.8Â° and 0.0Â±2.1Â° for rotation around the aforementioned axes.
Results: For all the tested clinical scenarios, translational motion estimates with our method had sub-mm accuracy (mean) and precision (standard deviation) while rotational motion estimates were accurate to <1Â° and precise to 2Â°. With the largest imaging update interval (30s), the errors were 0.1Â±0.6mm, -0.0Â±0.7mm and 0.1Â±0.9mm for translation in LR, SI and AP, respectively, and 0.1Â±1.3Â°, -0.3Â±2.0Â° and 0.1Â±0.9Â° for rotation around the aforementioned axes for both VMAT and IMRT treatments.
Conclusion: We developed and evaluated a novel method for highly accurate real-time 6DoF motion monitoring by synergistically combining continuous external signal and intermittent imaging. Our method thus enables real-time 6DoF motion monitoring for patients on a standard linac without requiring continuous high frequency kV imaging.
Funding Support, Disclosures, and Conflict of Interest: D T Nguyen is funded by an NHMRC and Cancer Institute New South Wales Early Career Research Fellowship. P Keall is funded by an NHMRC Senior Principal Research Fellowship.