Technical Note: Evaluation of the Latency and the Beam Characteristics of a Respiratory Gating System Using an Elekta Linear Accelerator and a Respiratory Indicator Device, Abches

Purpose: To evaluate the basic performance of a respiratory gating system using an Elekta linac and an Abches respiratory-monitoring device.

Methods: The gating system was comprised of an Elekta Synergy linac equipped with a Response gating interface module and an Abches respiratory-monitoring device. The latencies from a reference respiratory signal to the resulting Abches gating output signal and the resulting monitor-ion-chamber output signal were measured. Then, the flatness and symmetry of the gated beams were measured using a two-dimensional ionization chamber array for fixed and arc beams, respectively. Furthermore, the beam quality, TPR , and the output of the fixed gated beams were also measured using a Farmer chamber. Each of the beam characteristics was compared with each of those for nongated irradiation.

Results: The full latencies at beam-on and beam-off for 6-MV gated beams were 336.4 ± 23.4 ms and 87.6 ± 7.1 ms, respectively. The differences in flatness between the gated and nongated beams were within 0.91% and 0.87% for the gun-target and left-right directions, respectively. In the same manner, the beam symmetries were within 0.68% and 0.82%, respectively. The percentage differences in beam quality and beam output were below 1% for a beam-on time range of 1.1-7 s.

Conclusion: The latency of the Elekta gating system combined with Abches was found to be acceptable using our measurement method. Furthermore, we demonstrated that the beam characteristics of the gating system using our respiratory indicator were comparable with the nongated beams for a single-arc gated beam delivery.