Author: Alexander Baikalov, Luke Connell, Nolan M. Esplen, Michele M. Kim, Stephen F. Kry, Emil Schueler, Hayden Scott, Ryan Sun, Paige A. Taylor, Uwe Titt 👨🔬
Affiliation: The University of Texas MD Anderson Cancer Center, University of Pennsylvania, UT MD Anderson Cancer Center, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center 🌍
Purpose: to develop an affordable, portable device for accurately measuring FLASH dose rates from protons, electrons, and photons. 4 detectors were utilized to measure the temporal structure of proton spills, photon pulses, and electron pulses to a high degree of accuracy and consistency, allowing for an affordable and portable device to assist in remote audits for Imaging and Radiation Oncology Core’s commissioning of FLASH units.
Methods: Semiconductor detectors, including PTW flashDiamond, Exradin D1H diode, FD11A silicone photodiode, and FGA01 InGaAs photodiode, were tested. Detectors were operated via a Red Pitaya StemLab124-15 microcontroller. Proton doses (4, 8, 20 Gy) were delivered in single spills, while 9 MeV electrons were delivered at 1 Gy and 4 Gy per pulse. 16MeV and 16MV photons were generated from a clinic with photons generated from a lead scattering plate. Data acquisition ranged from 125 MHz to 61 kHz, depending on beam delivery timescales. Measurements included proton spill length (compared to a reference monitor chamber) and electron and photon pulse timing (compared to a Beam Current Transformer).
Results: The flashDiamond and Exradin D1H demonstrated <2% error in timing measurements with an average error of 0.5 ± 0.5% across all modalities. Photodiodes showed higher errors (>60%) due to slower fall-off times. For multi-pulse beams, all detectors achieved inter-pulse timing errors within 1%, averaging 0.8 ± 0.7%. Accuracy of timing between pulses (T) does not change with increasing sampling frequency
Conclusion: The flashDiamond and D1H diode effectively measure proton, 16e and 9 Mev electron, and generated photon FLASH dose rates at MHz frequencies. For remote QA and commissioning of FLASH beamlines, the flashDiamond and D1H provide great precision in dose rate assessments.