Feasibility Study - Extending the Clinical Utility of Optically Stimulated Luminescent Dosimeters (OSLDs)
Abstract
Purpose
While Optically Stimulated Luminescent Dosimeters (OSLDs) are widely used in clinical radiotherapy, their utility is typically limited to an accumulated dose of 10 Gy due to the filling of deep electron traps that causes sensitivity changes. This study evaluates UV-assisted annealing as a high-energy method to clear deep electron traps, aiming to restore consistency and extend the clinical lifespan of OSLDs through an analysis of UV energy and time dependence
Methods
Measurements were performed using a microSTARii® reader and a custom bleaching chamber equipped with both conventional fluorescent lamps and UV-C sources (254 nm). The study utilized nine "clinically retired" nanoDot OSLDs, all featuring accumulated dose histories exceeding 15 Gy. The evaluation was conducted in two stages. First, annealing reproducibility was tested by subjecting the OSLDs to repeated 24-hour UV cycles; between cycles, calibration curves were generated using a 6 MV beam with field of 10x10cm2 at doses from 50 to 1000 MU. Second, energy dependence was analyzed by exposing a separate set of OSLDs to 6, 10, and 18 MV photon fields (10x10cm2) at 100 and 400 MU. This allowed for a comparison of cleaning efficacy and recovery consistency across different radiation energy levels
Results
Preliminary analysis of the nine OSLDs demonstrated that calibration curves remained statistically consistent across multiple 24-hour annealing cycles. The reproducibility of the calibration slopes was high, with the standard deviation of the mean ranging from 3.58% to 7.12% across the study set.
Conclusion
The consistency in post-anneal calibration curves suggests that UV bleaching effectively extends OSLD utility beyond a 10 Gy lifetime dose. However, prior to clinical adoption, end-to-end testing must be performed to ensure measurement accuracy within a standard clinical workflow.