Technical Note: Characterization of clinical linear accelerator triggering latency for motion management system...

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Radiation Therapy

Background:

• Motion management systems in radiation therapy require precise timing for data acquisition, processing, and linac triggering.
• Existing latency guidelines often treat clinical linear accelerator (linac) triggering time as a fixed parameter.
• Decoupling linac-specific latency is crucial for accurately assessing and optimizing overall system performance.

Purpose of the Study:

• To develop a method for separating linac-only triggering latency from total system latency.
• To analyze the impact of accelerator settings on linac triggering latency.
• To enable latency considerations focused on linac-independent system components.

Main Methods:

• Measured linac-only triggering latency by comparing beam-on/off signal times with observed linac response.
• Utilized a multichannel oscilloscope, custom gating box, and in-isocenter diode for precise timing analysis.
• Investigated latency dependencies across various energies (6/18 MV) and repetition rates (100-600 MU/min).

Main Results:

• Linac triggering latency is dependent on accelerator repetition rate and energy settings.
• Beam-on latency decreased with higher repetition rates and lower energies; beam-off latency showed inverse trends.
• Observed latencies ranged from 3.37/1.45 ms (6 MV) to 6.02/0.73 ms (18 MV) at 600 MU/min; negative latencies were noted.

Conclusions:

• Linac triggering latency contributes minimally to the total allowable latency in motion management systems.
• The majority of system latency is attributable to linac-independent factors.
• This decoupling allows for more focused optimization of linac-independent system components.