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Changes in optically stimulated luminescent dosimeter (OSLD) dosimetric characteristics with accumulated dose
Author(s) -
Jursinic Paul A.
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3267489
Subject(s) - dosimeter , optically stimulated luminescence , materials science , luminescence , nanodot , radiochemistry , dosimetry , nuclear medicine , optoelectronics , chemistry , medicine
Purpose A new type of in vivo dosimeter, an optically stimulated luminescent dosimeter (OSLD), has now become commercially available for clinical use. The OSLD is a plastic disk infused with aluminum oxide doped with carbon(Al 2 O 3 : C ) . Crystals ofAl 2 O 3 : C , when exposed to ionizing radiation, store energy that is released as luminescence (420 nm) when the OSLD is illuminated with stimulation light (540 nm). The intensity of the luminescence depends on the dose absorbed by the OSLD and the intensity of the stimulation light. The effects of accumulated dose on OSLD response were investigated. Methods The OSLDs used in this work were nanodot dosimeters, which were read with a MicroStar reader (Landauer, Inc., Glenwood, IL). Dose to the OSLDs was delivered by 6 MV x rays and gamma rays from Co‐60 and Ir‐192. The signal on the OSLDs after irradiation is removed by optical annealing with a 150 W tungsten‐halogen lamp or a 14 W compact fluorescent lamp was investigated. Results It was found that OSLD response to dose was supralinear and this response was altered with the amount of accumulated dose to the OSLD. The OSLD response can be modeled by a quadratic and an exponential equation. For accumulated doses up to 60 Gy, the OSLD sensitivity (counts/dose) decreases and the extent of supralinear increases. Above 60 Gy of accumulated dose the sensitivity increases and the extent of supralinearity decreases or reaches a plateau, depending on how the OSLDs were optically annealed. With preirradiation of OSLDs with greater than 1 kGy, it is found that the sensitivity reaches a plateau 2.5 folds greater than that of an OSLD with no accumulated dose and the supralinearity disappears. A regeneration of the luminescence signal in the dark after full optical annealing occurs with a half time of about two days. The extent of this regeneration signal depends on the amount of accumulated dose. Conclusions For in vivo dosimetric measurements, a precision of ±0.5% can be achieved if the sensitivity and extent of supralinearity is established for each OSLD and use. Methods are presented for accomplishing this task.