# Markerless tumor tracking for lung SBRT with the Radixact Synchrony system: Initial experience and short‐term clinical outcomes

## TL;DR

This paper reports on the early clinical use of a new lung SBRT technique that tracks tumors without markers, showing it is feasible and effective with good short-term results.

## Contribution

The study presents initial clinical outcomes of a markerless tumor tracking technique for lung SBRT using the Radixact Synchrony system.

## Key findings

- Treatment was successfully delivered in all patients with median beam-on and treatment durations of 9.1 and 14.5 minutes.
- Dosimetric QA showed gamma passing rates >93% and <2% deviation in point dose under motion.
- At 9 months follow-up, local control was 100% with no grade ≥2 toxicities observed.

## Abstract

To report the initial clinical experience with the radixact synchrony lung with respiratory (LWR) technique in stereotactic body radiotherapy (SBRT) for lung tumors, focusing on feasibility, dosimetric performance, and early clinical outcomes using both standard and extended fractionation regimens.

Twenty patients with primary or metastatic lung tumors were treated using the Synchrony LWR technique. Patients were selected based on respiratory stability and favorable imaging characteristics. All patients underwent a Synchrony simulation, which included tumor tracking volume (TTV) definition and kV radiograph acquisition to assess their suitability for treatment with this technique. Treatment plans were generated using Precision TPS with VoloUltra. Plan verification, including gamma analysis and point dose measurements, was performed using the PTW Octavius system and dynamic motion QA. Synchrony model parameters, treatment times, and intrafraction interruptions were analyzed. Clinical follow‐up included imaging and toxicity assessment.

Treatment was successfully delivered in all patients with median beam‐on and treatment durations of 9.1 and 14.5 min, respectively. The median number of intrafraction interruptions was 1.95, and none of the fractions were canceled due to prolonged delivery. The mean kV imaging dose per fraction was 0.90 cGy. Dosimetric QA under motion showed gamma passing rates >93% and < 2% deviation in point dose. At a median follow‐up of 9 months, the local control rate was 100%, with no grade ≥2 toxicities observed.

The Radixact Synchrony LWR technique enables efficient and non‐invasive respiratory motion management in lung SBRT. This early experience demonstrates its feasibility with clinically acceptable delivery accuracy and promising short‐term clinical outcomes.