Author: David P. Adam, William T. Hrinivich, Taoran Li, Alexander Lu, Michael Salerno, Alejandro Sisniega, Boon-Keng Kevin Teo 👨🔬
Affiliation: Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, Johns Hopkins University, University of Pennsylvania 🌍
Purpose: Cone beam CT (CBCT)-guided online adaptive radiotherapy (ART) is of growing interest, with recent improvements in image quality provided through larger detector panels and fast gantry rotation. However, the impact of patient motion on CBCT-guided ART tasks using fast protocols is not fully understood. This study assesses the impact of periodic motion on CBCT-guided ART tasks using two novel fast CBCT systems.
Methods: A rigid anthropomorphic abdomen phantom was imaged using two CBCT systems with acquisition times of 16.6 s and 6 s (CB-16.6 and CB-6) and a diagnostic fan-beam CT (FB-0.5). Periodic motions with varying amplitudes (±0.5-10 mm) and a constant 4 s period were applied during imaging. All images were initially rigidly and then subsequently deformably registered to the reference FB-0.5 image of the stationary phantom. Image quality was assessed across motion amplitudes for each imaging system in terms of geometric distortion using motion vector field (MVF) magnitude, deep learning-based auto-contouring accuracy using dice similarity coefficient (DSC), and simulated dose delivery accuracy following a synthetic CT-based ART workflow using Paddick conformity index (CI).
Results: Mean±standard deviation (SD) MVF magnitudes across motion amplitudes for the FB-05, CB-16.6, and CB-6 scanners were 0.89±0.47 cm, 0.12±0.12 cm, and 0.20±0.17 cm, respectively. Following auto-contouring, mean [ranges] of DSC values for the FB-0.5, CB-16.6, and CB-6 scanners were 0.78 [0.39-0.99], 0.62 [0.19-0.86] and 0.67 [0.28-0.86], respectively. Following simulated ART, mean±SD difference in CI values for the FB-0.5, CB-16.6, and CB-6 scanners were -0.12±0.13, -0.00±0.02, and -0.01±0.02, respectively.
Conclusion: CB-16.6 and CB-6 provided high-quality images for ART. Compared to FB-0.5, fast CBCT exhibited increased blurring and streaking but significantly less geometric distortion with increasing motion. Faster CBCT (6 s vs. 16.6 s) reduced blur, improving auto-contouring accuracy, but the interplay between the motion period and 6 s image acquisition must be carefully managed.