Measurement of the temporal latency of a respiratory gating system using two distinct approaches.

Purpose: To develop a methodology that can be used to measure the temporal latency of a respiratory gating system.

Methods: The gating system was composed of an automatic gating interface (Response) and an in-house respiratory motion monitoring system featuring an optically tracked surface marker. Two approaches were used to measure gating latencies. A modular approach involved measuring separately the latency of the gating system's complementary metal-oxide-semiconductor tracking camera, tracking software, and a gating latency of the LINAC. Additionally, an end-to-end approach was used to measure the total latency of the gating system. End-to-end latencies were measured using the displacement of a radiographic target moving at known velocities during the gating process.

Results: Summing together the latencies of each of the modular components investigated yielded a total beam-on latency of 1.55 s and a total beam-off latency of 0.49 s. End-to-end beam-on and beam-off latency was found to be 1.49 and 0.34 s, respectively. In each case, no statistically significant differences were found between the end-to-end latency of the gating system and the summation of the individually measured components.

Conclusion: Two distinct approaches to quantify gating latencies were presented. Measuring the end-to-end latency of the gating system provided an independent means of validating the modular approach. It is expected that the beam-on latencies reported in this work could be reduced by altering the control system configuration of the LINAC. The modular approach can be used to decouple the individual latencies of the gating system, but future improvements in the temporal resolution of the service graphing feature are needed to reduce the uncertainty of LINAC-related gating latencies measured using this approach. Both approaches are generalizable and can be used together when designing a quality assurance program for a respiratory gating system.