Evaluation of MgB4O7:Ce, Li and Ce-doped 80MgB2O4–20MgB4O7 as alternative OSL materials for use in quality assurance of 6 MV photon beams

Abstract

We investigated the potential use of two new borate matrices for quality assurance (QA) tests in radiotherapy. Both matrices, MgB4O7:Ce, Li (MBO) and Ce-doped 80MgB2O4–20MgB4O7 (80-20MBO), were doped with 0.5% cerium oxide. The following dosimetric properties of these materials prepared as pellets were tested: optically stimulated luminescence (OSL) sensitivity, dose response, fading, reproducibility, and the supralinearity index. Subsequently, the pellets were exposed to a 6 MV photon beam, and the percentage depth dose (PDD) curve, OSL response to different dose rates, and radiation field size dependencies were compared with those obtained with a reference detector (ionization chamber, I.C.) used in QA. The results indicated a higher OSL sensitivity of 80–20MBO as compared with MBO, on the order of 6- to 8-fold. The dose response of MBO presented a linear behavior within the range evaluated (20 mGy–2 Gy), unlike 80-20MBO, which had a supralinear behavior. The OSL signal of 80–20MBO was also marked by 60% fading within 5 h post irradiation; afterwards, the OSL signal stabilized. A better reproducibility of 80–20MBO compared with MBO was also observed. No dose rate dependence of the OSL response was observed; moreover, a maximum 5% standard deviation was seen in this test. For the field size tests, the pellets over-responded by 3.1% (80-20MBO) and 3.4% (MBO), in a 3 × 3 cm2 field, compared with the I.C. For the PDD, a high deviation was observed if compared with the I.C. data at the build-up region (at a depth d ≤ 2 cm), maximum 4.3% and 7.8% for 80-20MBO and MBO, respectively, and beyond this value, good agreement among detectors was seen. Our preliminary results indicate the potential utility of these pellets in QA for radiotherapy.