Author: Morgan Aire, Krystal M. Kirby, Olivia Magneson, David E. Solis, Hamlet Spears 👨🔬
Affiliation: Louisiana State University, Mary Bird Perkins Cancer Center 🌍
Purpose: This study evaluates the range of motion of abdominal organs using 4D stack-of-stars magnetic resonance (MR) imaging and 4D computed tomography (CT), the current clinical standard. Accurate organ motion measurement is crucial for internal target volume (ITV) development and optimizing motion management techniques like the compression belt. While patients using compression belts typically undergo two 4DCT scans, resulting in additional radiation dose, 4DMR can provide equivalent motion tracking with no ionizing radiation and superior soft tissue contrast.
Methods: 4DCT and 4DMR images were acquired according to standard clinical protocol and retrospectively binned. Abdominal organs were segmented in the minimum and maximum exhale phases using an AI-based auto-contouring algorithm for 4DCT, and manual, dosimetrist-verified delineation for 4DMR. Organ contours were compared using three metrics: centroid distance, Hausdorff distance, and mean distance to agreement. Various 4DMR reconstruction metrics were assessed with Mutual Information and Joint Histograms. Additionally, compression belt placement reproducibility was analyzed via contours on each daily adaptive image set.
Results: Range of motion measurements were independent of the number of bins used in 4DMR reconstruction. Furthermore, the average specific organ motion estimates between 4DMR and 4DCT agreed within <1mm (0.84mm), with average absolute differences for the left kidney (0.85mm), right kidney (0.58mm), liver (1.48mm), and spleen (0.7mm).
Conclusion: Variability in compression belt placement likely contributed significantly to motion differences. This study compared 4DMR with 4DCT to assess organ motion, demonstrating that 4DMR provides comparable range values to CT, the current gold standard. These findings support the potential clinical application of 4DMR, especially for motion management in radiation therapy planning. Further evaluation of compression belt reproducibility is necessary to understand the impact of sub-mm motion differences.