Author: Fan Liu, Adam C. Riegel, Yi-Fang Wang 👨🔬
Affiliation: Columbia University Irving Medical Center 🌍
Purpose: HyperSight, Varian Medical Systems' latest CBCT technology, integrates rapid 6-second data acquisition with advanced iterative reconstruction, enabling precise real-time contouring and dose calculation for online adaptive radiotherapy. Effective motion management, particularly for thoracoabdominal tumors, remains challenging due to complex motion trajectories. While slow CBCT captures motion effectively, it may introduce artifacts from the reconstruction assumptions. This study evaluates motion imaging accuracy by comparing slow CBCT, single fast CBCT scans, and averaged images from repeated fast scans.
Methods: Respiratory motion was simulated using a CIRS dynamic thorax phantom with a 2 cm target insert, employing a Cos6 motion pattern (superior-inferior amplitudes: 5, 10, and 20 mm; cycle time: 6s). HyperSight imaging was performed using protocols thorax slow (58.6s) and thorax fast (5.9s) with iCBCT Acuros reconstruction algorithm. In addition, ten repeated fast scans were averaged to create a composite average CBCT. 4DCT average scans served as the reference standard. Imaging artifacts were assessed, and HU values and internal target volume (ITV) sizes from HyperSight images were compared with the reference.
Results: Despite streaking artifacts in slow scans, both slow scans and averaged fast scans generated motion images with ITV sizes closely matching 4DCT, differing by less than 1 cc across all amplitudes. HU values from these scans were consistent with 4DCT references, showing variations of less than 40 HU. Conversely, single fast scans exhibited significant deviations, with 40–50% larger ITV sizes and 7-40% lower mean HU values, due to artifacts from short acquisition times.
Conclusion: Slow scans and averaged fast scans outperform single fast scans for imaging moving targets, making them critical for online adaptive radiotherapy. Averaged fast scans, in particular, have the potential to produce artifact-free motion images. Future studies will explore developing phase-resolved fast CBCT, further advancing motion imaging and treatment precision for online adaptive radiotherapy.