Characterization of a Time-Resolved, Real-Time Scintillation Dosimetry System for Ultra-High Dose-Rate Radiation Therapy Applications.

Purpose: Scintillation dosimetry has promising qualities for ultra-high-dose-rate (UHDR) radiation therapy (RT), but no system has shown compatibility with mean dose rates (DR¯) above 100 Gy/s and doses per pulse (D) exceeding 1.5 Gy typical of UHDR (FLASH)-RT. The aim of this study was to characterize a novel scintillation dosimetry system with the potential of accommodating UHDRs.

Methods And Materials: We undertook a thorough dosimetric characterization of the system on an UHDR electron beamline. The system's response as a function of dose, DR¯, D, and the pulse dose-rate (DR) was investigated, as was 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 ±3%, the system exhibited dose linearity and was independent of DR¯ and D within the tested ranges of 1.8 to 1341 Gy/s and 0.005 to 7.68 Gy, respectively. A 6% reduction in the signal per unit dose was observed as DR was increased from 8.9e4 to 1.8e6 Gy/s. The dose delivered per integration window of the continuously sampling photodetector had to remain between 0.028 and 11.56 Gy to preserve a stable signal response per unit dose. The system accurately measured D of individual pulses delivered at up to 120 Hz. The day-to-day variation of the signal per unit dose in a reference setup varied by up to ±13% but remained consistent (<±2%) within each treatment day and showed no signal loss as a function of dose history.

Conclusions: With daily calibrations and DR-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 and offering diverse applications to FLASH-RT and related fields.