Precision of RL/OSL medical dosimetry with fiber-coupled Al2O3:C: Influence of readout delay and temperature variations

Carbon-doped aluminum oxide (Al2O3:C) crystals attached to 15 m optical fiber cables can be used for online in vivo dosimetry during, for example, remotely afterloaded brachytherapy. Radioluminescence (RL) is generated spontaneously in Al2O3:C during irradiation, and this scintillator-like signal enables real-time monitoring of the dose delivery. Furthermore, the crystal acts as a passive optically stimulated luminescence (OSL) dosimeter, and the accumulated dose for a full treatment can be obtained while the dosimeter is still in the patient by optical stimulation with a low-power laser. The prime objective of this work was to assess the influence of delay between irradiation and optical stimulation on such measurements. A secondary objective was to demonstrate that previously determined RL/OSL temperature coefficients are independent of the delay between irradiation and OSL readout. These coefficients account for changes in RI and OSL signals with changes in temperature during irradiation and stimulation. The work was primarily based on a set of automated laboratory measurements carried out using 50 kV X-rays (0-3 Gy) with delays in the range of 10-3600 s and temperatures in the range of 10-45 degrees C. The test protocol involved randomization of five experimental parameters (irradiation dose, two temperatures, and two delays). The main finding was that the delay between irradiation and OSL readout has a small (0.5% for a 1 h delay) but significant influence on the OSL-signals, but none on the temperature coefficients. (C) 2009 Elsevier Ltd. All rights reserved