The analysis of readout values according to reading methods: Glass dosimeter reader

Abstract

The accuracy and precision of dose measurement using a glass dosimeter (GD) depend on appropriate and stable operation of the GD reader. The aim of this study is to evaluate the stability of readout values of the reader and to recommend effective use of reading methods for reducing the uncertainty in dosimetric performance through the investigation of characteristics of a GD-based reader system. The examined glass dosimetry system consists of silver-activated metaphosphate GD element and a fully automatic readout system. GD elements were calibrated and exposed using a Co-60 teletherapy unit (Theratron 780, AECL, Kanata, Canada). The reproducibility of repeated measurements results show that the readout value is 0.4% lower at fifth measurement, 0.9% lower at tenth measurement, and 1.3% lower at the twentieth measurement, compared to the reference value. The resulting readout values of the GD elements according to the loading positions were at minimum 0.5% lower, and at maximum, 3.1% higher, with an average of 2.0% higher values compared to the reference readout value in the first position. The interface effect for dose due to the loading number of GD elements was evaluated to be 1.015, 1.022, and 1.035 times higher in the average dose values for the loading of five GD elements, ten GD elements, and twenty GD elements than the average readout value at the first position, respectively. As a result, in order to get an accurate and precise dose measurement by the GD reader, if repeated readings are performed, measured values should be corrected according to the number of repeated readings, and the loading of GD elements in the magazine should constantly be kept in the same position. Moreover, the number of GD elements loading on the magazine should be decided by considering either accurate and precise dose measurements or numerous relative dose measurements.