Characterization of optically stimulated luminescent dosimeters, OSLDs, for clinical dosimetric measurements.

Optically stimulated luminescent dosimeters, OSLDs, are plastic disks infused with aluminum oxide doped with carbon (Al2O3 : C). These disks are encased in a light-tight plastic holder. Crystals of Al2O3 : 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. OSLDs used in this work were InLight/OSL Dot dosimeters, which were read with a MicroStar reader (Landauer, Inc., Glenwood, IL). The following are dosimetric properties of the OSLD that were determined: After a single irradiation, repeated readings cause the signal to decrease by 0.05% per reading; the signal could be discharged by greater than 98% by illuminating them for more than 45 s with a 150 W tungsten-halogen light; after irradiation there was a transient signal that decayed with a 0.8 min halftime; after the transient signal decay the signal was stable for days; repeated irradiations and readings of an individual OSLD gave a signal with a coefficient of variation of 0.6%; the dose sensitivity of OSLDs from a batch of detectors has a coefficient of variation of 0.9%, response was linear with absorbed dose over a test range of 1-300 cGy; above 300 cGy a small supra-linear behavior occurs; there was no dose-per-pulse dependence over a 388-fold range; there was no dependence on radiation energy or mode for 6 and 15 MV x rays and 6-20 MeV electrons; for Ir-192 gamma rays OSLD had 6% higher sensitivity; the dose sensitivity was unchanged up to an accumulated dose of 20 Gy and thereafter decreased by 4% per 10 Gy of additional accumulated dose; dose sensitivity was not dependent on the angle of incidence of radiation; the OSLD in its light-tight case has an intrinsic buildup of 0.04 g/cm2; dose sensitivity of the OSLD was not dependent on temperature at the time of irradiation in the range of 10-40 degrees C. The clinical use of OSLDs for in vivo dosimetric measurements is shown to be feasible.