SU-E-T-312: Optically Stimulated Luminescent Dosimeter Performance in High Dose Rate Brachytherapy.

PURPOSE To investigate the use of optically stimulated luminescent dosimeters (OSLDs) for high dose rate (HDR) Ir-192 brachytherapy. While common in megavoltage radiotherapy applications, the performance of OSLDs using kilovoltage energies, high dose gradient and high dose rate regions ubiquitous to HDR has not been demonstrated. METHODS Commercially available nanoDotTM (Landauer, Glenwood, IL) OSLDs - 5mm diameter and 0.2mm thickness - were irradiated using an Ir-192 source in various geometries to determine dose rate dependence. Angular geometries were created using a circular applicator designed for accelerated partial breast irradiation by Accuboost®. RESULTS Response remained linear for high doses and was independent of dose rate. Specifically, the OSLDs were shown to be linear with dose up to 200 cGy then became slightly supra-linear up to 600 cGy. There was a slight angular dependence for OSLDs which becomes significant in 'edge-on' scenarios. An asymmetry in this angular dependence was discovered, but was attributed to cable curvature, point source approximation, and positioning within its plastic casing. CONCLUSIONS Clinical HDR doses of 300 cGy fall within the linear, dose-rate-independent region. Angular independence can be maintained by avoiding extreme 'edge-on' measurement geometries. Because of re- readability, OSLDs can serve as a permanent record or alternatively be annealed within a few hours using conventional fluorescent light. Lastly, OSLDs are produced for only $5 each. Due to these features, in conjunction with the dosimetric performance, OSLDs should be considered a reliable tool for in vivo HDR brachytherapy measurements.