Optically Stimulated Luminescent Dosimeters Stable Response to Dose after Repeated Bleaching.

PURPOSE 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 OSLD 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 pre-irradiated 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 has been pre-irradiated 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. Pre-irradiated nanoDots that were bleached with light without UV content had stable dose sensitivity (±1.5%), stable linearity factor (±3.5%) for over 10 bleaching cycles, non-linear response that was quadratic in dose, and dose measurement uncertainty of ±1.4% 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 pre-irradiated 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 pre-irradiated and bleached with light without UV content. Dose can be measured with an uncertainty of 1.4%, which is a 3 fold reduction of the uncertainty found with the single use batch method recommended by the manufacturer.