Technical note: High‐dose and ultra‐high dose rate (UHDR) evaluation of Al₂O₃:C optically stimulated luminescent dosimeter nanoDots and powdered LiF:Mg,Ti thermoluminescent dosimeters for radiation therapy applications

Abstract

BackgroundDosimetry in ultra‐high dose rate (UHDR) electron beamlines poses a significant challenge owing to the limited usability of standard dosimeters in high dose and high dose‐per‐pulse (DPP) applications.PurposeIn this study, Al2O3:C nanoDot optically stimulated luminescent dosimeters (OSLDs), single‐use powder‐based LiF:Mg,Ti thermoluminescent dosimeters (TLDs), and Gafchromic EBT3 film were evaluated at extended dose ranges (up to 40 Gy) in conventional dose rate (CONV) and UHDR beamlines to determine their usability for calibration and dose verification in the setting of FLASH radiation therapy.MethodsOSLDs and TLDs were evaluated against established dose‐rate–independent Gafchromic EBT3 film with regard to the potential influence of mean dose rate, instantaneous dose rate, and DPP on signal response. The dosimeters were irradiated at CONV or UHDR conditions on a 9‐MeV electron beam. Under UHDR conditions, different settings of pulse repetition frequency (PRF), pulse width (PW), and pulse amplitude were used to characterize the individual dosimeters’ response in order to isolate their potential dependencies on dose, dose rate, and DPP.ResultsThe OSLDs, TLDs, and Gafchromic EBT3 film were found to be suitable at a dose range of up to 40 Gy without any indication of saturation in signal. The response of OSLDs and TLDs in UHDR conditions were found to be independent of mean dose rate (up to 1440 Gy/s), instantaneous dose rate (up to 2 MGy/s), and DPP (up to 7 Gy), with uncertainties on par with nominal values established in CONV beamlines (± 4%). In cross‐comparing the response of OSLDs, TLDs and Gafchromic film at dose rates of 0.18–245 Gy/s, the coefficient of variation or relative standard deviation in the measured dose between the three dosimeters (inter‐dosimeter comparison) was found to be within 2%.ConclusionsWe demonstrated the dynamic range of OSLDs, TLDs, and Gafchromic film to be suitable up to 40 Gy, and we developed a protocol that can be used to accurately translate the measured signal in each respective dosimeter to dose. OSLDs and powdered TLDs were shown to be viable for dosimetric measurement in UHDR beamlines, providing dose measurements with accuracies on par with Gafchromic EBT3 film and their concurrent use demonstrating a means for redundant dosimetry in UHDR conditions.

A comprehensive investigation of the performance of a commercial scintillator system for applications in electron FLASH radiotherapy

“…For dosimetric reporting, the BCTs were calibrated against dose-rate-independent radiochromic film whereby the signal measured by the BCT was correlated with the dose measured in Gafchromic film thereby creating a calibration factor at each reference setup for the W2 placed in solid water as previously reported. 6,[41][42][43][44] All measurements reported in this study are the average of three consecutive measurements. The error bars used represent two standard deviations taken from three consecutive measurements.…”

“…However, the clinical translation of FLASH‐RT is hindered by challenges related to accurate dosimetry and real‐time beam monitoring 7,8 . Detectors that have been established to be dose‐rate independent include passive detectors such as radiochromic film, thermoluminescent dosimeters, optically stimulated luminescence dosimeters, and alanine‐based dosimeters 7–11 . Despite their dose‐rate independence, these passive detectors require a post‐irradiation wait time to achieve the signal stabilization required for accurate measurements 7,12–16 .…”