The effect of different bleaching wavelengths on the sensitivity of Al2O3:C optically stimulated luminescence detectors (OSLDs) exposed to 6 MV photon beams
Authors: Omotayo Azeez A. , Cygler Joanna E. , Sawakuchi Gabriel O. 
Published: August 2012

Purpose:

To determine the effect of different bleaching wavelengths on the response of Al2O3:C optically stimulated luminescence detectors (OSLDs) exposed to accumulated doses of 6 MV photon beams.

Methods:

In this study the authors used nanoDot OSLDs readout with a MicroStar reader. The authors first characterized the dose–response, fading, and OSL signal loss of OSLDs exposed to doses from 0.5 to 10 Gy. To determine the effect of different bleaching wavelengths on the OSLDs’ response, the authors optically treated the OSLDs with 26 W fluorescent lamps in two modes: (i) directly under the lamps for 10, 120, and 600 min and (ii) with a long‐pass filter for 55, 600, and 2000 min. Changes in the OSLDs’ sensitivity were determined for an irradiation‐readout–bleaching‐readout cycle after irradiations with 1 and 10 Gy dose fractions.

Results:

The OSLDs presented supralinearity for doses of 2 Gy and above. The signal loss rates for sequential readouts were (0.287 ± 0.007)% per readout in the reader's strong‐stimulation mode, and (0.019 ± 0.002)% and (0.035 ± 0.007)% per readout for doses of 0.2 and 10 Gy, respectively, in the reader's weak‐stimulation mode. Fading half‐life values ranged from (0.98 ± 0.14) min to (1.77 ± 0.24) min and fading showed dose dependence for the first 10‐min interval. For 10 and 55 min bleaching using modes (i) and (ii), the OSL signal increased 14% for an accumulated dose of 7 Gy (1 Gy fractions). For OSLDs exposed to 10 Gy fractions, the OSL signal increased 30% and 25% for bleaching modes (i) and (ii) and accumulated dose of 70 Gy, respectively. For 120 and 600 min bleaching using modes (i) and (ii), the OSL signal increased 2.7% and 1.5% for an accumulated dose of 7 Gy (1 Gy fractions), respectively. For 10 Gy fractions, the signal increased 14% for bleaching mode (i) (120 min bleaching) and decreased 1.3% for bleaching mode (ii) (600 min bleaching) for an accumulated dose of 70 Gy. For 600 and 2000 min bleaching using modes (i) and (ii), the signal increased 2.3% and 1.8% for an accumulated dose of 7 Gy (1 Gy fractions), respectively. For 10 Gy fractions, the signal increased 10% for mode (i) (600 min bleaching) and decreased 2.5% for mode (ii) (2000 min bleaching) for an accumulated dose of 70 Gy.

Conclusions:

The dose–response of nanoDot OSLDs read using the MicroStar reader presented supralinearity for doses of 2 Gy and above. The signal loss as a function of sequential readouts depended on dose. Fading also depended on dose for the first 10‐min interval. For dose fractions of 1 and 10 Gy, OSLDs may be reused within 3% and 5% accuracies up to the maximum accumulated dose of 7 and 70 Gy investigated in this study, respectively. These accuracies were obtained after the OSLDs were bleached with a light source with wavelengths above about 495 nm. The authors also concluded that changes in sensitivity of OSLDs depended on bleaching time, accumulated dose, and wavelength spectrum of the bleaching source.