Preliminary Investigation into the regeneration of luminescent signal in nanoDot OSLDs

Abstract

Purpose Reuse of optically stimulated luminescent dosimeters (OSLDs) has been suggested in prior works by using a light source to erase the dosimeter’s signal (optical bleaching) and recharacterizing the dosimeter’s sensitivity based on its dose history. However, depending on the wavelength of the bleaching source and the dosimeter’s dose history this may be problematic due to the presence of deep dosimetric traps and the phototransfer mechanism observed in Al2O3. In this work we examine the regeneration of signal in OSL nanoDots, with prior irradiation history, following their bleaching from a light source containing blue wavelengths. Methods Irradiations were performed on 33 nanoDots at a dose range of 5–3000 cGy using 6 MV and 1000–3000 cGy using 220 kV x rays, with three nanoDots irradiated at each dose value. Following their irradiation, nanoDots were bleached using blue light for a period of 1 h. The postbleached signal in nanoDots was measured over a 27‐day period to track any changes in their measured signal due to the migration of charge carriers from deep dosimetric traps to shallower traps of the dosimeter. Results The growth extent and growth rate observed in bleached nanoDots were observed to be dependent on the dosimeter’s accumulated dose history and energy of the radiation source. The 12 nanoDots with prior irradiation history of 500, 1000, 2000, and 3000 cGy from 6 MV x rays exhibit an increase in measured signal that range from 220 to 5229 PMT counts when measured the first day postbleaching to 408–8710 PMT counts when measured on the 27th day postbleaching, which may be substantial depending on the application regarding the dosimeter's reuse. Conclusion These findings caution against the reuse and optical bleaching of nanoDots with prior irradiation history exceeding 100 cGy and demonstrate an energy, accumulated dose, and time dependence in the regeneration of signal in postbleached nanoDots with prior irradiation history.

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

“…Examining the dose-response curves for OSLDs, TLDs, and Gafchromic film at the extended dose range reveal that the sensitivity of OSLDs and TLDs increases with accumulated dose owing to the filling of the deep traps with increasing dose, whereas the sensitivity of Gafchromic film decreases owing to saturation in the amount of radiation-induced polymers as a function of dose. 14,20,39 Here we found that the dose response of OSLDs and TLDs irradiated under UHDR beamlines was within ± 4% of their expected values calibrated under reference conditions in CONV beamlines, which is well within the uncertainty established for OSLDs and TLDs published in TG-191, 20 regardless of the DPP, mean dose rate, or instantaneous dose rate investigated. This is especially important given that the uncertainty of film has been reported to be 2−5% 1,47,48 in FLASH dosimetry, with an overall uncertainty of EBT3 film in UHDR beams of < 4% (k = 2), 30 with the quality of dose-rate independence.…”

“…The first equation used for OSLDs and TLDs is a linear equation that is bounded by the signal (kPMT or μC/g) measured at 2 Gy, which is below the threshold for supralinearity measured in both dosimeters. 20,[38][39][40][41] We developed two separate equations by using bounds for the measured signal ranging from 2 to 13 Gy and from 13 to 40 Gy to ensure greater accuracy in parsing the delivered dose within a narrower range of values. These higher doses were investigated because of their relevance in stereotactic RT and FLASH RT, where high-dose single fractions (≥ 8 Gy) are routinely delivered.…”

“…Our method allows users to generate a curve‐fitting function by using either a single polynomial or multiple polynomial equations to correlate Gafchromic film, OSLD, and TLD measurements to the delivered dose. The first equation used for OSLDs and TLDs is a linear equation that is bounded by the signal (kPMT or μC/g) measured at 2 Gy, which is below the threshold for supralinearity measured in both dosimeters 20,38–41 . We developed two separate equations by using bounds for the measured signal ranging from 2 to 13 Gy and from 13 to 40 Gy to ensure greater accuracy in parsing the delivered dose within a narrower range of values.…”

“…At low‐dose ranges, using a linear coefficient may be appropriate, but at the higher doses relevant to FLASH RT, such methods would no longer be suitable because of the nonlinear response of TLDs with dose, as demonstrated here. Examining the dose‐response curves for OSLDs, TLDs, and Gafchromic film at the extended dose range reveal that the sensitivity of OSLDs and TLDs increases with accumulated dose owing to the filling of the deep traps with increasing dose, whereas the sensitivity of Gafchromic film decreases owing to saturation in the amount of radiation‐induced polymers as a function of dose 14,20,39 …”

Dose-response dependencies of OSL dosimeters in conventional linacs and 1.5T MR-linacs: an experimental and Monte Carlo study

“…Moreover, there are several advantages of OSLDs over other types of dosimeters, including high sensitivity, reproducibility, and tissue equivalence , Dunn et al 2013, Hoshida et al 2019. They are also re-usable, easy-to-implement (Liu 2020) and relatively cost-effective, i.e. good candidates for dosimetry QA checks, remote dosimetry and audit tests (Jahn et al 2014, Hoshida et al 2019, Kido et al 2023.…”