Dual-Plane 3D-Motion Tracking In 0.35T MR-Guided SBRT: Balancing Target Coverage and OAR Protection In Liver Cancer
Abstract
Purpose
This study aimed to evaluate the clinical feasibility of a dual-target 3D-motion tracking workflow for 0.35T MRI-guided stereotactic body radiotherapy (MRgRT) in upper abdominal targets. The focus was on implementing real-time, dual-plane tracking to enable high-precision automatic beam gating, with beam-on gating for the target and beam-off gating for the organs-at-risk (OAR).
Methods
A pilot clinical workflow was established using a dual-target phantom for commissioning. The protocol was then applied to a patient with primary liver cancer located adjacent to the bowel. The workflow integrated dual-plane tracking, simultaneous monitoring of two tracking objects, and OAR dose accumulation. Data from five treatment fractions were analyzed, including cine-MRI parameters, tracking thresholds, respiratory motion patterns, and overall delivery efficiency.
Results
The initial fraction required a beam-on time of 35 minutes, which exceeded the predicted 11.8 minutes (based on a 50% duty cycle). However, through workflow optimization, subsequent fractions showed marked improvement, with the final fraction completed in 9 minutes. The clinical team successfully managed dual-plane parameters by defining tracking boundaries based on the relative motion between the tumor and the large bowel. This approach ensured robust gating even with tighter margins for the primary target.
Conclusion
We demonstrated the clinical feasibility of dual-plane 3D-motion tracking in 0.35T MRgRT. This workflow allows for the simultaneous monitoring of tumors and critical structures, significantly enhancing OAR sparing without compromising treatment efficiency.