Author: Jeremy T. Booth, Nicholas Hardcastle, Freeman Jin, Alicja Kaczynska, Paul J. Keall, Chandrima Sengupta 👨🔬
Affiliation: Northern Sydney Cancer Centre, Royal North Shore Hospital, Physical Sciences, Peter MacCallum Cancer Centre, Image X Institute, Faculty of Medicine and Health, University of Sydney, Image X Institute, Faculty of Medicine and Health, The University of Sydney 🌍
Purpose: An ESTRO survey reported that 71% of radiotherapy centers across 41 countries want to implement real-time image guided radiation therapy (IGRT) to improve patient outcomes. To address this global demand, this research developed and investigated an accessible real-time 6 degrees-of-freedom (6DoF) IGRT technology using internal-external motion correlation (6D-IEC) modelling. 6D-IEC provides continuous, low-dose real-time target translation and rotation information using standard radiotherapy equipment.
Methods: The 6D-IEC technology has three steps: model building, real-time IGRT, and model updating. Model building optimizes a correlation model between internal tumor motion observed via fiducial markers on 2D CBCT projections with simultaneously acquired external patient surface motion measurements. Real-time IGRT continuously estimates 6DoF target motion using periodically acquired intra-treatment 2D projections and continuous external measurements. Model updating occurs concurrently with real-time IGRT to account for spatiotemporal variations in the internal-external motion correlation model. The 6D-IEC technology’s performance was evaluated using a real-time image simulator with patient-measured 2D CBCT and intra-treatment projection images and external motion traces from three free-breathing liver SBRT treatments. Geometric accuracy was quantified by the mean and standard deviation of the differences between the real-time 6D-IEC technology results and the continuous Kilovoltage Intrafraction Monitoring system, assumed as the ground truth.
Results: A real-time software based on the 6D-IEC technology was developed that displays the real-time 6DoF motion estimates on its interface. For the investigated tumor traces, real-time 6D-IEC IGRT achieved mean ± standard deviation motion estimation errors of 0.2±1.7 mm, -0.9±2.6 mm, and -0.0±1.2 mm along the left-right, superior-inferior, and anterior-posterior translational axes, and -0.1°±1.4°, 0.5°±1.9°, and 0.3°±1.3° around the corresponding rotational axes.
Conclusion: The real-time 6D-IEC technology accurately monitored 6DoF liver tumor motion, paving the way for experimental investigations followed by clinical translation. This technology could increase motion management accessibility for abdominal and thoracic SBRT patients, potentially improving patient outcomes.