Idea for Preparing the Stabilizing Optically Stimulated Luminescence (OSL) Dosimeter Having Smaller Signal Depletion

We plan to apply Optically Stimulated Luminescence (OSL) dosimeters to the quality assessment of delivered dose from a clinical linear accelerator (linac). To manage the output dose appropriately, it is important to measure the absorbed dose to water with high accuracy. There is an issue of sensitivity variation of commercially available OSL dosimeter reading devices with uncertainty being the major component of concern. Previously, a monitoring method to solve this issue was proposed, but this conventional method is too complex to use in clinical facilities. This is because signal instability of an OSL dosimeter, which is used as a monitoring dosimeter, should also be corrected. In order to establish a simple monitoring method, we focused our attention on the development of a signal-stabilized dosimeter for use as a monitoring dosimeter. This study aims to propose a novel idea for processing the dosimeter leading to less signal depletion after multiple readings. Our idea to reduce the number of electrons trapped at the shallow energy level, which is the cause of signal depletion, is to perform partial bleaching on the commercial dosimeter after irradiating at a high dose. OSL dosimeters were prepared under several conditions first we used irradiation doses of 10 and 50 Gy and then exposure to visible light for 0, 10, 30, and 60 seconds. After processing, the OSL signals were read out using a commercial reader, and the signal depletion rate and statistical uncertainty were analyzed. When comparing the results for 10 Gy and 50 Gy, the statistical uncertainty became smaller after irradiating at a high dose. From the results of different bleaching times, we found that signal depletion rate related to one reading can be reduced by partial bleaching; however statistical uncertainty became larger with increased bleaching time. When performing 50 Gy irradiation at 30-second bleaching times, we can prepare a dosimeter having good characteristics of signal depletion rate of -0.007 % and statistical uncertainty of 0.33 %.