Room: AAPM ePoster Library
Purpose: Verification of an in-vivo dosimetry method using optically stimulated luminescent dosimeters (OSLD, nanoDotTM, Landauer Inc., Glenwood Il) within a prostate-designed ultrasound phantom.
Methods: First, irradiated OSLDs were read out pre- and post- removing the crystal from its light-tight case in order to understand the dose effects resulting in the handling of the crystals. Next, crystals from irradiated OSLDs were exposed for various amounts of time to ambient light in order to understand the optical anneal effects of the OSLD crystals outside of their light-tight case. Finally, computed tomography (CT) scan of OSLD crystals positioned on an ultrasound probe inserted into a CIRS phantom was generated for dose planning in Elekta Oncentra treatment planning system (TPS). The OSLD crystals were contoured in the TPS and the dose to the crystals was determined from the dose volume histogram. Using the Elekta Oncentra HDR afterloader, a CT-based HDR plan delivered 200 cGy to the surface of the US probe.
Results: Signal variations on the OSLD reading due to mechanical distress (from removing and reinserting the OSLD crystal) and optical annealing (when the crystal was exposed to ambient light) were found to be -0.93% ± 1.8% and 0.56% per minute ± 0.12% per minute. The average discrepancy between the treatment planning system dose and the dose measured from the CF-OSLDs was found to be 4.52% ± 2.54%.
Conclusion: The method developed in this study shows minimal variation in OSLD measurements with careful handling of the crystals, resulting in strong agreement between TPS-calculated dose and the CF-OSLD phantom measurements.