Long-Term Reliability of Optically Stimulated Luminescence Dosimeters

Abstract

Optically stimulated luminescence dosimeters (OSLDs) can be used as accurate and re-usable dosimeters for radiotherapy applications. OSLDs have been observed to decline in sensitivity with repeated use and it is important to determine whether this decline in sensitivity is associated with a decline in reliability. This study used three batches of OSLDs (purchased in 2012, 2014 and 2016) that had been repeatedly re-used in a mature in vivo dosimetry programme over a period of up to five years and evaluated the consistency of their response over repeated irradiation-readout-bleaching cycles. Each irradiation delivered 105 cGy to all OSLDs, using a 12 meV electron beam from a Varian iX linear accelerator. The five- and three-year-old OSLDs respectively displayed 86% and 89% of the sensitivity of the one year old OSLDs, but when a correction factor for each OSLD was derived based on the first measurement result and applied to each subsequent reading, all OSLDs were able to measure the 105 cGy test dose accurately, within standard deviations of 2.0% for the OSLDs from 2012 and 1.3% for the OSLDs from 2014 and 2016. If a mean calibration value was applied to the readings from each batch of OSLDs, instead of applying a measurement-derived sensitivity correction factor to each individual OSLD reading, the standard deviations increased to an unacceptable 6.1, 5.6 and 2.9%. Well-used three- and five-year-old OSLDs were shown to be capable of providing measurements with similar accuracy to a more recently-purchased batch of OSLDs, when measurement-derived sensitivity correction factors were applied to each result. If this extra step is included in the OSLD measurement process, then the same OSLDs may be reliably used for years without needing to be retired and replaced.