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Stray Radiation Triggered Imaging of Clinical Radiotherapeutic Beams

M Ashraf*, P Bruza , B Pogue , Dartmouth College, Hanover, NH


(Tuesday, 7/31/2018) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 8

Purpose: CCD cameras are often employed to image scintillation and Cherenkov radiation in external beam radiotherapy, and this is often achieved by gating the camera to the linear accelerator (Linac) output using a physical trigger cable. However, this approach can induce delay in the trigger signal, and feedback to the Linac can be a potential hazard to the Linac performance. In this work, a scintillating detector for stray radiation inside the Linac room was developed to act as an untethered trigger for camera-based dosimetry, thereby overcoming the issues of delay and linac performance problems.

Methods: A crystal scintillator was coupled to a SiPM counting module. The detector was systematically placed at various locations in the room and tested with X-Rays and electron beams of different energies and field sizes. Two different scintillator sizes were used for the study. The false trigger rate and aspects were recorded due to background and residual radioactivity. The detector was also used in a standard Total Skin Electron Therapy setup.

Results: For X-Ray beams, the module triggers 130-80ns before the linac target current signal output line. The detector provided ample output voltage for the camera to trigger for distances up to 2.5 m from the isocenter with a 6MV, 5x5cm beam and 3x3x20mm crystal. With a larger scintillator size, the detector could be placed even beyond 3.0m distance. The jitter in the module’s output around the threshold level was limited by the jitter in the Linac’s output signal.

Conclusion: The module can be used for different radiotherapeutic procedures with beams of various field sizes and energies and is particularly useful for remote Cherenkov imaging or remote scintillator dosimetry imaging. Moreover, this module overcomes the delay caused by direct wire-based triggering and can act as instantaneous Linac pulse monitor.

Funding Support, Disclosures, and Conflict of Interest: Financial support by National Institute of Health (NIH) grants R01 EB023909 and R44 CA199681


Not Applicable / None Entered.


IM- Multi-modality imaging systems: Development (new technology and techniques)

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