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

## TL;DR

This case study explores using a biliary stent to track tumor motion during radiation therapy for pancreatic cancer, but faces challenges with accuracy and reliability.

## Contribution

The study demonstrates the potential and limitations of using biliary stents as motion surrogates in real-time adaptive SBRT for pancreatic cancer.

## Key findings

- Biliary stents showed minimal motion discrepancy with the tumor in initial assessments.
- Stent rotation and signal interruptions led to tracking failures and treatment abortion.
- Alternative free-breathing approaches were used after tracking failures.

## Abstract

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.