Characterization of a novel time-resolved, real-time scintillation dosimetry system for ultra-high dose rate radiation therapy applications

Abstract: Background: Scintillation dosimetry has promising qualities for ultra-high dose rate (UHDR) radiotherapy (RT), but no system has shown compatibility with mean dose rates ($\bar{DR}$) above 100 Gy/s and doses per pulse ($D_p$) exceeding 1.5 Gy typical of UHDR (FLASH)-RT. The aim of this study was to characterize a novel scintillator dosimetry system with the potential of accommodating UHDRs. Methods: A thorough dosimetric characterization of the system was performed on an UHDR electron beamline. The system's response as a function of dose, $\bar{DR}$, $D_p$, and the pulse dose rate ${DR}_p$ was investigated, together with the system's dose sensitivity (signal per unit dose) as a function of dose history. The capabilities of the system for time-resolved dosimetric readout were also evaluated. Results: Within a tolerance of $\pm$3% the system exhibited dose linearity and was independent of $\bar{DR}$ and $D_p$ within the tested ranges of 1.8-1341 Gy/s and 0.005-7.68 Gy, respectively. A 6% reduction in the signal per unit dose was observed as ${DR}_p$ was increased from 8.9e4-1.8e6 Gy/s. Additionally, the dose delivered per integration window of the continuously sampling photodetector had to remain between 0.028 and 11.64 Gy to preserve a stable signal response per unit dose. The system accurately measured $D_p$ of individual pulses delivered at up to 120 Hz. The day-to-day variation of the signal per unit dose at a reference setup varied by up to $\pm$13% but remained consistent (<$\pm$2%) within each day of measurements and showed no signal loss as a function of dose history. Conclusions: With daily calibrations and ${DR}_p$ specific correction factors, the system reliably provides real-time, millisecond-resolved dosimetric measurements of pulsed conventional and UHDR beams from typical electron linacs, marking an important advancement in UHDR dosimetry.