ESTRO 2022 - Abstract Book

S14

Abstract book

ESTRO 2022

Simulations of geometrical consequences of the gating latencies were based on the cranio-caudal motion during the first treatment field of 15 patients previously treated with liver SBRT guided by internal electromagnetic motion monitoring (Calypso). Amplitude-based respiratory gating with approximately 50% duty cycle around the exhale phase was simulated for all patients. Geometrical errors caused by gating latencies were quantified as the percentage of the total time beam- on time spent outside the gating window (Fig.2A). Results The mean (±SD) gate-on latencies were 270.8±37.2ms (ProBeam) and 86.2±12.8ms (TrueBeam), respectively. Gate-off latencies were 103.6±16.2ms (ProBeam) and 44.5±11.6ms (TrueBeam). For simulated treatments based on these latencies, the mean time with beam-on outside the gating windows was 6.7% [patient range:3.7-10.0] for ProBeam and 3.5% [1.8-5.5] for TrueBeam (Fig.2B). For gate-off latencies ≤ 104ms, the beam-on time with errors above 1mm were below 5% for all patients (Fig.2C). Conclusion Gating latencies were measured based on beam visualization by a scintillating crystal. The TrueBeam had smaller latencies than the ProBeam. For both accelerators, the latencies only resulted in minor geometrical errors.