A radiophotoluminescent glass plate system for medium-sized field dosimetry

Abstract

A two-dimensional radiophotoluminescent system for medium-sized field dosimetry has been developed using a silver-activated phosphate glass plate with a dimension of 120mm×120mm×1mm and a readout unit comprising a UV excitation lamp and a CCD imager. A dose ranging from 0 to 400 cGy, provided by a 6 MV x-ray beam, was delivered to the glass plate oriented perpendicularly to the beam and positioned in a water phantom at a depth of 10 cm, where the center of the glass plate coincided with the linac isocenter. After the dose delivery, the glass plate was placed in the readout system. The CCD output intensity increased linearly with the applied dose. The angular dependence of response on the direction of radiation incidence was measured by rotating the glass plate in the water phantom, indicating that the output remained constant up to 75° from perpendicular incident direction, followed by a steep reduction down to 85% at an angle of 90°. A lateral dose distribution resulting from a 60mm×60mm irradiation was compared between the glass plate and an x-ray film having had the same exposure, showing that the glass plate and the x-ray film led to identical dose distributions. The dose reproducibility for a glass plate and the sensitivity variation among different glass plates were also evaluated.