Plastic optical fibres (POF) made of polymethyl methacrylate (PMMA) have several advantages over traditional optical fibres, including lower cost, the possibility of larger diameters and better mechanical resistance. These properties make them an attractive option for sensor technologies, including radiation dosimetry. This paper compares PMMA optical fibre with pure silica core optical fibre. Both fibres are useful for ionising radiation measurements. To evaluate the effect of ionising radiation, we have developed and designed a measurement system that allows continuous measurement of attenuation during the ionising radiation irradiation process. We used a technique that measured changes in laser power transmitted through an optical fibre at a constant gamma radiation dose rate.