Abstract
This paper presents an initial investigation into the depth dependence of an inorganic optical fibre sensor (OFS) based on physical measurements and Monte Carlo (MC) simulations, using a 6 MV flattening filter free (FFF) beam. The OFS was fabricated using an inorganic scintillating material (Gd2O2S: Tb), which was embedded in a cavity of diameter 700 mu m, in a 1mm plastic optical fibre. Percentage depth dose (PDD) profiles were measured in a solid water phantom for three field sizes: 10x10 cm(2), 4x4 cm(2) and 2x2 cm(2). The OFS results were then compared to an ion chamber and the W1 plastic scintillator. A MC model of an Elekta Versa HD linear accelerator (linac) was developed using the MC software packages BEAMnrc and DOSXYZnrc and then used to simulate the Gd2O2S: Tb and polystyrene scintillators. The OFS measurements over-estimated the dose when compared to the ion chamber and the W1 measurements, across the investigated field sizes, by a maximum of 30%, 20% and 15% for 10x10 cm(2), 4x4 cm(2) and 2x2 cm(2), respectively. The MC simulations of the Gd2O2S: Tb and polystyrene scintillators were in good agreement with the W1 and ion chamber measurements, however, the OFS measurements were found to differ across all field sizes. Our results therefore indicate the need for further investigation into the overall contribution of the stem effect to the discrepancy between the OFS physical measurements and the ion chamber and the W1 measurements.