Calibration and time fading characterization of a new optically stimulated luminescence film dosimeter

Background Optically stimulated luminescence (OSL) dosimeters produce a signal linear to the dose, which fades with time due to the spontaneous recombination of energetically unstable electron/hole traps. When used for radiotherapy (RT) applications, fading affects the signal‐to‐dose conversion and causes an error in the final dose measurement. Moreover, the signal fading depends to some extent on treatment‐specific irradiation conditions such as irradiation times. Purpose In this work, a dose calibration function for a novel OSL film dosimeter was derived accounting for signal fading. The proposed calibration allows to perform dosimetry evaluation for different RT treatment regimes. Methods A novel BaFBr:Eu2+‐based OSL film (Zeff, 6 MV = 4.7) was irradiated on a TrueBeam STx using a 6 MV beam with setup: 0° gantry angle, 90 cm SSD, 10 cm depth, 10 × 10 cm2 field. A total of 86 measurements were acquired for dose‐rates (Ḋ$\dot{D}$) of 600, 300, and 200 MU/min for irradiation times (tir) of 0.2, 1, 2, 4.5, 12, and 23 min and various readout times (tscan) between 4 and 1440 min from the start of the exposure (beam‐on time). The OSL signal, S(Ḋ,tir,tscan)$S(\dot{D},{t}_{ir},{t}_{scan})$, was modeled via robust nonlinear regression, and two different power‐law fading models were tested, respectively, independent (linear model) and dependent on the specific tir${t}_{ir}$ (delivery‐dependent model). Results After 1 day from the exposure, the error on the dose measurement can be as high as 48% if a fading correction is not considered. The fading contribution was characterized by two accurate models with adjusted‐R2 of 0.99. The difference between the two models is