SU-E-T-130: Evaluation of Optically Stimulated Luminescent Dosimeters as An In-Vivo Dosimeter for Breast Surface Dose Measurement

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Abstract

Purpose: Evaluation of the optically stimulated luminescence (OSL) system for surface dose measurement for breast radiation therapy techniques. Methods: Landauer InLight OSL were calibrated on a Varian 21EX linac using an ion chamber with 6 MV beam. The response of OSL, TLD and a parallel plate chamber were compared at the surface of a solid water phantom and also under reference conditions (10×10cm2 at depth 5cm). OSL angular dependence, reproducibility, linearity, and inter-OSL variability were investigated. Radiation therapy treatment plans were generated for an anthropomorphic breast phantom (RANDO). Eleven locations were identified and 2 OSL and 3 TLD were placed at each location. Treatment was delivered under clinical conditions. The OSL and TLD were evaluated for dose response. Results: The average response of the OSL to dose as compared to the ion chamber was found to be within 6% under reference conditions and the TLD within 2.5%. The factor of surface response to response at depth was found to be 0.284 for the Markus chamber, 0.425 for the OSLˈs and 0.434 for the TLD. No angular dependence was found for the OSL. The reproducibility of the batch response given 100 cGy was within 1%. The linearity of the OSL displayed an R2 value of 0.9997. The OSL given 100 cGy under reference conditions had a maximum deviation from average of 2.6%. Discrepancies on the IMRT plan between TLD and OSL ranged from 0.1% to 6.5% for the dose>50cGy and between 3.5% and 38.9% for the dose≤50cGy Conclusions: OSL and TLD are over-responding to surface dose with respect to the parallel plate ion chamber. OSL have been found to respond similarly to TLD at the surface of an anthropomorphic phantom.

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