Jaydev Dave, Presenter: Nothing to Disclose

Eric Laurence Gingold PhD, Abstract Co-Author: Nothing to Disclose

The propagation of error in incremental OSL measurements limits the accuracy and precision for diagnostic dosimetry. The bleaching process re-establishes the dark noise to levels comparable to new dosimeters, thereby showing a resolution on the order of 0.3 mGy for doses as low as 0.6 mGy.

To investigate the performance of optically-stimulated luminescence (OSL) dosimeters (OSLDs) in incremental dose mode, and when optical bleaching is used between measurements.

Dark noise levels were determined for 19 screened new OSLDs (Landauer, Glenwood, IL, USA) using a microStar reader (Landauer). Sixteen OSLDs were randomly divided into groups of 4 (3 OSLDs reserved as control). A 4x4 experimental design was used to verify the effects of treatment (doses 2.5, 5, 10 and 20 mGy; also measured using a calibrated ion chamber) and the order of incremental dose.  Each group (with a cumulative dose of 37.5 mGy) was randomly exposed to an additional dose in the range of 2.5 to 11.5 mGy to test OSLDs’ accuracy with resident dose.  The OSLDs were bleached for 20 hours with a fluorescent light (27W, 6400K) and exposed to doses in the range of 0.6 to 2 mGy to verify post-bleaching performance.

New OSLDs recorded a dark noise of 0.10±0.01 mGy. Pooling data from all 4 treatment groups resulted in a significant correlation (r2 = 0.994; p < 0.001) of doses recorded by OSLDs with the ion chamber. The measured incremental dose error was the least (6%) when the treatment levels increased monotonically, but this error was as high as 39% for relatively low doses of 2.5 and 5 mGy following a dose of 10 or 20 mGy.  With a cumulative resident dose on the OSLDs of 38.34±1.14 mGy, additional dose in the range of 2.5 to 11.5 mGy resulted in a significant difference (p<0.001) between OSLDs dose and the ion chamber dose, and not all of the discrete OSLD dose steps were significantly distinguishable. Post-bleaching, the OSLDs dark noise decreased to 0.11±0.01 mGy. Following bleaching, the OSLDs dose showed a significant correlation (r2=0.991; p<0.001) with the ion chamber dose and a significant difference (p<0.05) between all the discrete dose steps from 0.6 to 2 mGy.

Dave, J, Gingold, E, Reusability of OSL Dosimeters in Diagnostic Radiology Applications.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11015406.html