Abstract:
Background Particle therapy is highly sensitive to respiratory motion, and low-latency respiratory gating is essential to ensure dose accuracy. Surface-guided radiation therapy (SGRT), featuring continuous monitoring and a non-ionizing workflow, is increasingly adopted in particle therapy and has become an important approach to respiratory gating. However, validation of gating latency for SGRT-guided proton and heavy ion systems remains limited in this area.
Purpose To measure the gate-on and gate-off latencies of an SGRT-proton and heavy ion radiotherapy system using two different methods, compare the two experimental approaches, and evaluate the latency performance of the SGRT-guided system to inform its clinical application.
Methods Two measurements were conducted using a PPL film method and a high-speed camera-detector method. In the film method, a proton beam traversed a 1.5-mm-diameter aperture in a lead collimator, producing on the film a striped pattern that encodes latency; the films were digitized at 0.10 mm resolution for analysis. In the camera-detector method, a 240 frames/s high-speed camera recorded the instant the gating condition was met, and gate-on and gate-off delays were computed from the time difference to the detector-registered radiation signal. End-to-end latency was measured with both methods, and results were cross-validated using combined uncertainty.
Results The gate-on latency measured by the film method and the camera–detector method was 79 ms±10 ms and 67 ms±10 ms, respectively; the corresponding gate-off latency was 101 ms±9 ms and 129 ms±5 ms. Across two measurement methods, gate-on latencies were concordant within the combined standard uncertainty, whereas gate-off latency showed a significant method-dependent discrepancy, indicating systematic bias.
Conclusions The SGRT-proton and heavy ion gating system meets our clinical requirements. This study demonstrates the feasibility and necessity of multi-method cross-validation of gating latency and provides quantitative evidence for the commissioning and acceptance test of SGRT in particle therapy.
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