Pulse Resolved Beam Characterization and Feedback for FLASH-RT Using Radioluminescent Dosimeters
M Ashraf1*, M Rahman1, R Zhang2, B Williams2, J Hoopes1,D Gladstone2, B Pogue1, P Bruza 1(1) Dartmouth College, Thayer Engineering, Hanover, NH,(2) Dartmouth-Hitchcock Med. Ctr., Lebanon, NH
Presentations
TU-F-TRACK 5-5 (Tuesday, 7/27/2021) 4:30 PM - 5:30 PM [Eastern Time (GMT-4)]
Purpose: Beam monitoring for FLASH-RT is challenging due to ultra-high dose rate conditions. In this study, dose-rate independent radioluminescent based techniques are presented for pulse-resolved beam characterization and real-time feedback to a FLASH enabled Linac.
Methods: A modified clinical linac delivered a radially symmetric 10 MeV electron FLASH beam (~300 Gy/s, 1 Gy/Pulse) to isocenter. Lateral projected 2D dose distributions for each linac pulse were imaged in a fluorophore-doped water tank using a time-gated camera. An inverse Abel transform reconstruction provided 3D images for on-axis depth dose values. The central axis depth dose values were compared against film data. For pulse-by-pulse feedback, a scintillating point dosimeter was coupled to a gated integrator and a field programmable gate array (FPGA)-based control system.
Results: The camera images were reconstructed at a spatial resolution of 0.5 mm. The Dmax, R₅₀, and Rp measured with film and camera based method agreed to within 1 mm for a 1.5 cm circular beam and the beam with jaws wide open (40 x 40 cm²). Central axis cross beam profiles for both beams agreed with film data with > 95% passing rate (2%/2mm gamma criteria). Beam energy measurements based on the R50 criteria using optical measurements revealed a stable beam energy between adjacent pulses. However, a ramp-up period was observed where the dose per pulse increased for the first few pulses and then stabilized. The dose-read out scheme for individual pulses using the gated integrator and the FPGA based system was characterized.
Conclusion: Radioluminescence based techniques were presented as a high spatio-temporal resolution technique for online monitoring of FLASH beams. The presence of a ramp-up requires that feedback to the Linac should be based on dose accumulation. Therefore, the gated integrator and the FPGA based control system can enable accurate feedback for FLASH.
Handouts
Keywords
Scintillators, Dosimetry, Optical Dosimetry
Taxonomy
TH- Radiation Dose Measurement Devices: Development (new technology and techniques)
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