Abstract
When optical fibre dosimetry systems are exposed to ionizing radiation, unwanted Cerenkov radiation and fluorescent light are produced in the fibre itself during irradiation. A number of techniques have been used to eliminate or minimize these effects. In this study time discrimination technique was used, by measuring the signal of an inorganic scintillation detector between linac pulses, after the stem effect signal has decayed to successfully eliminate the contribution of Cerenkov radiation. Dosimetric properties, including the repeatability of the ISD system response and angular dependence of the system, were tested. Percentage depth dose profiles were measured for different field sizes and compared to ion chamber measurements. The result of this study shows that the ISD system has good repeatability of the output signal when exposed to high and low radiation doses with a maximum deviation of 0.55% and 1.10%, respectively. However, the system showed a strong angular dependence in the azimuthal plane due to the detector shape. Additionally, the system overestimates the dose when measuring PDDs, this effect decreased with the decrease in field sizes.