Technical Note: Time-gating to medical linear accelerator pulses: Stray radiation detector

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Radiation Detection

Background:

• External beam radiotherapy utilizes Charge-Coupled Device (CCD) cameras for imaging scintillation and Cherenkov radiation.
• Camera gating to the linear accelerator (Linac) output is crucial for accurate imaging.
• Direct Linac output signals can be inaccessible or cause electrical feedback issues.

Purpose of the Study:

• To develop a remote scintillating detector for timing linac pulses.
• To enable camera-based dosimetry without direct electrical connection to the Linac.
• To overcome limitations of wired triggering in radiotherapy imaging.

Main Methods:

• A scintillator coupled silicon photomultiplier detector was optimized for sensitivity and beam compatibility (X-rays, electrons).
• Cherenkov radiation imaging was performed using both remote and wired triggers for comparison.
• A coincidence detection scheme was implemented to mitigate false-positive triggering from neutron-activated products.

Main Results:

• The remote detector circuit provided sufficient voltage (>2.5 V) up to 3m from the isocenter for a 6 MV beam.
• Larger scintillator sizes allowed for placement beyond 3m.
• Coincidence detection effectively reduced false-positive triggering.
• Time-gated imaging showed negligible fluctuations compared to wired triggering.

Conclusions:

• The developed remote detector offers untethered synchronization to linac pulses.
• It is particularly valuable for remote Cherenkov or scintillator dosimetry imaging.
• This technology enhances radiotherapy procedures where direct linac signal access is limited.