Optically stimulated luminescent dosimeters stable response to dose after repeated bleaching

Abstract

To investigate the dose response of optically stimulated luminescent dosimeters (OSLDs), and how this response changes with repeated use, increased accumulated dose, and bleaching light with or without a UV component. To devise a method to stabilize dose response characteristics of OSLDs that are used repeatedly. To decrease measurement uncertainty. Methods: Optically stimulated luminescent dosimeters irradiations were made using a linear accelerator and Ir-192. The OSLDs (InLight nanoDots) dose response was characterized for these various irradiations under the batch, single use, method and the repeated irradiation method. Some nanoDots were preirradiated with hundreds of Gray of dose with Ir-192 gamma rays. Repeated use OSLDs were bleached with lights that had different UV content. A special bleaching light was fabricated and used that had the same spectrum as the light in the OSLD reader. Results: New, never irradiated, nanoDots had their characteristics altered by illumination with bleaching light that had a UV component. Each new nanoDot had unique sensitivity to dose as well as a unique linearity factor, which was supra-linear. NanoDots that were irradiated and bleached repeatedly had changes in low and high dose sensitivity that was altered if the bleaching light had UV in its spectrum. For nanoDots that have been preirradiated with up to 1500 Gy of dose, their dose response was supra-linear for bleaching light without UV content and infra-linear for light with UV content. Preirradiated nanoDots that were bleached with light without UV content had stable dose sensitivity (AE1.5%), stable linearity factor (AE3.5%) for over 10 bleaching cycles, nonlinear response that was quadratic in dose, and dose measurement uncertainty of AE1.4% for 277 measurements. Conclusions: The UV component in bleaching light has an impact on the dose sensitivity characteristics shown by new or repeatedly irradiated nanoDots. Each new nanoDot has a unique sensitivity to dose as well as a unique linearity factor, which was supra-linear. As nanoDots accumulate dose with repeated use they change sensitivity to low and high dose very differently based on the UV content of the bleaching light. For nanoDots that have been preirradiated with hundreds of Gray of dose their dose response was supra-linear for bleaching light without UV content and infra-linear for light that has UV content. NanoDots can be used repeatedly and have stable dose response characteristics if they are preirradiated and bleached with light without UV content. Dose can be measured with an uncertainty of 1.4%, which is a threefold reduction of the uncertainty found with the single use batch method recommended by the manufacturer.

Preliminary Investigation into the regeneration of luminescent signal in nanoDot OSLDs

“…This supralinear response is attributed to the filling of the deep electron traps, in which at higher doses more free electrons are generated in the Al 2 O 3 :C crystalline structure that subsequently occupy the deep electron traps and enhance the signal from optically stimulated luminescence. 5 Jursinic 2010 5 first documents the regeneration of signal in OSL Because the filling of deep electron traps not only affects the measured nanoDot signal after their optical bleaching but also their sensitivity, 1,15 which was reported to be dependent on the bleaching time, accumulated dose, and wavelength of the bleaching source, 7 it is recommended that OSL nanoDots not be reused with a prior irradiation history exceeding 500 cGy to minimize any further uncertainties in dosimetric accuracy. For OSL nanoDots with a prior history of 100 cGy or less, the regeneration of signal due to the phototransfer of charge carriers was observed to be no >50 PMT counts when measured over a 27-day period, which is only substantial when reusing OSL nanoDots for very low dose exposures, on the order of several mGy.…”

“…Because the filling of deep electron traps not only affects the measured nanoDot signal after their optical bleaching but also their sensitivity, 1,15 which was reported to be dependent on the bleaching time, accumulated dose, and wavelength of the bleaching source, 7 it is recommended that OSL nanoDots not be reused with a prior irradiation history exceeding 500 cGy to minimize any further uncertainties in dosimetric accuracy. For OSL nanoDots with a prior history of 100 cGy or less, the regeneration of signal due to the phototransfer of charge carriers was observed to be no >50 PMT counts when measured over a 27‐day period, which is only substantial when reusing OSL nanoDots for very low dose exposures, on the order of several mGy 11 .…”

A disposable OSL dosimeter for in vivo measurement of rectum dose during brachytherapy

“…According to an AAPM report on the introduction of basic characteristics of OSL dosimeter, 35 commercial OSL dosimeters have a sensitivity variation of 2.2% (k = 1), and it has been reported [32][33][34] that this is due to the inhomogeneous distribution of air bubbles in the Al 2 O 3 :C layer. The uncertainty of our catheter dosimeter is larger than that of the OSL dosimeter itself.…”

“…Until now, many clinical trials have been performed using passive type dosimeters. Reports concerning thermo-luminescent dosimeters, 26 alanine/electron spin resonance (ESR) dosimeters, 27 and optically stimulated luminescence (OSL) dosimeters 25,[28][29][30][31][32][33][34][35] have been published. In this study, we focused our attention on the OSL dosimeter, which is composed of Al 2 O 3 :C, because this dosimeter has good characteristics for dosimetry in the medical field.…”

Technical note: Sources of systemic error in total body irradiation and total skin electron therapy in vivo measurements using nanoDot optically stimulated luminescence dosimeters within high‐efficiency clinics

“…4,9 Quality of the bleaching light source, specifically the ultraviolet light content, seems to affect dose responsivity beyond 10-20 Gy as well. 10,11 This study evaluates dose uncertainty in clinical TBI and TSET OSLD measurements based on a highly efficient and cost-saving clinical practice,where (1) dosimeters are repeatedly irradiated and bleached with a compact fluorescent light (CFL) until cumulative dose of 15 Gy was delivered, at which point they are discarded, (2) vendor-recommended element sensitivity S s,i , vendor is used to correct individual raw OSLD readings M raw , and (3) a quadratic fit is used on a batch-by-batch basis to relate S s,i , vendor -corrected readings, M corr , to actual dose. Directly adjacent pairs of dosimeters were used to monitor TBI and TSET point doses at each of the anatomical locations indicated in Figure 1.…”