Energy response of radiophotoluminescent glass dosimeter for diagnostic kilovoltage x-ray beams.

Abstract

This study aimed to investigate the energy response of a radiophotoluminescent glass dosimeter (RGD) for diagnostic kilovoltage x-ray beams by Monte Carlo (MC) calculations and measurements. The uniformity and reproducibility of GD-352M (with Sn filter) and GD-302M (no filter) were tested with 45 RGDs in free air. Subsequently, the RGD response was obtained as a function of an Al-HVL using the parameter, quality index (QI), which is defined as the ratio of the effective energy (keV) to the maximum energy (keV) of the photons. The x-ray fluence spectra with QI of 0.4, 0.5, and 0.6 were set for tube voltages of 50~137.6 kVp. The RGD response was calculated in free air using the MC method and verified by the air kerma, Kair, measured using an ionization chamber. The uniformity and reproducibility of the 45 RGDs were±2.3% and±2.7% for GD-352M and±0.7% and±1.6% for GD-302M at the one standard deviation level, respectively. The calculated RGD response was 0.965 to 1.062 at Al-HVL 2.73mm or more for GD-352M and varied from 3.9 to 2.8 for GD-302M. Both RGD responses exhibited a good correlation with the Al-HVL for the given QI. Kair measured by RGDs for each beam quality with a QI of 0.5 was in the range of -5%~0.8% for GD-352M and -1.8%~3% for GD-302M, relative to the chamber measurements. The RGD response was indicated as a function of the Al-HVL for the given QI, and it presented a good correlation with the Al-HVL.