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Time-Gated and Long-Pass Filtered Imaging of Photon and Proton Beams for 2-D and 3-D Beam Profiles

M Rahman*1, P Bruza1, R Zhang2 , V Borza1,3, B Pogue1,3, (1) Dartmouth College, Hanover, NH, (2) Emory Proton Therapy Center, Atlanta, GA, (3) Dose Optics, LLC, Lebanon, NH


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Radiographic scintillation screens with appropriate filtering were used to image dose delivery with time gated intensified CMOS camera remote imaging, creating direct instantaneous 2-D and 3-D profiles of photon and proton beams in water.

Methods: Green-600 scintillating screen was submerged and aligned with the water surface in a tank phantom. Screen properties (intensity decay, excitation, and emission spectra) and transmission spectra of varying long pass filters were explored. Camera captured Golden-Amber long pass filter attached screens’ scintillation images 10 microsecond and background images 2200 microsecond after radiation pulse for Cherenkov removal. Photon beams at 6-MV with 6 cm and 8 cm square fields and proton pencil beams at 150-MeV were imaged. The screen was shifted longitudinally on the patient couch at increments of 0.6 cm (-6 to 6 cm from isocenter) for photons and 0.2 cm (-2 to 2 cm from isocenter) for protons.

Results: Discrepancy between depth of max dose measured and accepted golden-beam data was 3.3 mm and 0.8 mm for protons and photons respectively. PDD and crossbeam profiles indicate a broadening of light captured for photons due to Cherenkov excitation of water and absorption by scintillating screen. Delayed image acquisition prevented camera from capturing direct Cherenkov light and filter attachment suppressed Cherenkov absorption by screen. Cherenkov-suppressed crossbeam agreed with golden-beam data and reduced the “spread� effect on photon images.

Conclusion: Long pass filter and delayed image acquisition after radiation beam pulse are essential to suppressing crosstalk and background in this application. With these approaches, using sequential movement of the couch placing the film off isocenter, and one beam-on event per slice, fast and accurate acquisition of profiles can be produced. In future work, imaged intensity will be calibrated to dose in phantom and 3-D beam profile acquisition will be automated with spatial translation through the beam.


Quality Assurance, Protons, Gating


TH- External Beam- Particle therapy: Proton therapy - quality assurance

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