Purpose: To develop a framework to evaluate dosimetric and temporal characteristics of a respiratory gating system.
Methods: We characterized the gating system dosimetrically and temporally using two distinct approaches. The gating system was composed of an automatic gating interface (Elekta Response™) and an in-house respiratory monitoring system featuring an optically tracked surface marker. Central-axis output and energy constancy were evaluated across 8 linear accelerators. Additionally, a representative set of 5 treatment plans were delivered both non-gated and gated on each accelerator to a 2D diode array (MapCHECK™). The surface marker was attached to a dynamic phantom (QUASAR™) which was programmed to replicate a typical DIBH breathing waveform. The passing rates between these modes of operation were evaluated using gamma analysis and a percent dose difference comparison. Modular and end-to-end approaches were used to quantify system latencies. The modular components studied included the optical tracking camera, sampling rate of the tracking software, signal travel time, and latency of the linear accelerator. The end-to-end approach involved measuring the displacement of a target moving at known velocities during the during the gating process.
Results: Output and energy constancy were both within ± 0.5% across each accelerator studied. The average difference in passing rates between non-gated and gated treatment deliveries were within ± 0.4% using gamma analysis (2%, 1mm). Average passing rates were greater than 99% using a percent dose difference comparison (1%). No significant difference was observed t(14)=0.21, p=.83, between the modular (M=1.55 seconds, SD= 0.25) and end-to-end (M=1.49 seconds, SD= 0.03) approaches used to quantify beam-on latency.
Conclusion: The proposed framework can be used to validate the operating characteristics of a respiratory gating system. The modular approach provides a convenient method to analyze the component latencies contributing to the end-to-end total.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by a funding from the Karnival Krewe de Louisiane and from the Investor Collective