Beam quality conversion factor of BeO-OSLD for high-energy photon beams

Abstract

Optically stimulated luminescence (OSL) dosimeters are used in radiotherapy. The beam quality conversion factor (kQ) of dosimeters is essential for correcting energy dependence. However, the kQ of an OSL dosimeter using BeO (BeO-OSLD) has not yet been reported for high-energy photon beams. In this study, the kQ of BeO-OSLD was investigated for high-energy photon beams using experiments and Monte Carlo calculations. In the experiments, kQ was evaluated as the ratio of calibration coefficients determined using high-energy photon beams and 60Co γ-rays. Ten OSL dosimeters were used to reduce the statistical uncertainty of the determined kQ values, and the same dosimeters were repeatedly used to obtain the data set of high-energy photon beams and 60Co γ-rays. Pre-irradiation with 10 Gy and bleaching were performed on fresh dosimeters before dosimetry to reduce the dependence of the detector response on the accumulated dose. In Monte Carlo calculations, both the absorbed dose to water and that of the BeO dosimeter for high-energy photon beams and 60Co γ-rays were calculated, and then kQ was determined using the ratio of these values. The determined kQ values in high-energy photon beam were 0.998 ± 0.011 and 1.021 ± 0.005 for the experiment and the calculation, respectively. These results showed that the variation in kQ for 6–25 MV was negligible in practical dosimetry. This result indicates that BeO can be used to evaluate doses for different beam qualities without correcting for energy dependence.