Real-Time Adaptive Respiratory Motion Compensation With Stent-Based Tracking.

Stereotactic body radiation therapy (SBRT) offers a promising treatment option for locally advanced pancreatic cancer, but its precision is challenged by respiratory-induced tumor motion. The Radixact Synchrony system integrates real-time motion tracking using internal and external surrogates, potentially enabling reduced treatment margins. In this case study, we report on an 85-year-old female patient with pancreatic cancer who underwent SBRT planning using an implanted biliary stent as a surrogate for tumor motion tracking. Initial assessments, including 4DCT analysis and Synchrony simulation, indicated minimal motion discrepancy between the stent and tumor, supporting its use as a tracking target. However, at the time of treatment, a ~25° rotation of the stent and intermittent external LED signal interruptions impaired motion model accuracy, leading to repeated tracking failures and treatment abortion. The patient was subsequently treated using a free-breathing internal target volume approach. This case highlights both the potential and limitations of using biliary stents as surrogates in real-time motion-adaptive SBRT. It underscores the need for robust quality assurance, improved tracking technologies, and consideration of online adaptive strategies to account for anatomical and surrogate variability. Further investigation is warranted to optimize motion management in pancreatic SBRT utilizing stents as tracking target surrogates.