With the increase in complexity of brachytherapy treatments, there is a demand for the development of sophisticated devices for dose delivery verification. An optical fibre sensor for monitoring low dose radiation is presented. The sensor is a Cerium doped Lutetium based scintillation crystal, LYSO (Lu1.8Y.2SiO5:Ce), provided by Saint-Gobain crystals, which was inserted into a 18G Mick Applicator Needle and coupled to a 1mm plastic optical fibre. The LYSO emits visible light when exposed to low level ionising radiation. The incident level of ionising radiation can be determined by analysing the optical emission. The sensor is designed for in vivo monitoring of the radiation dose during radio-active seed implantation for low dose rate (LDR) brachytherapy, in prostate cancer treatment, providing oncologists with real-time information of the radiation dose to the target area and/or nearby organs at risk (OARs). The radiation from the brachytherapy seeds causes emission of visible light from the scintillation material through the process of radioluminescence, which penetrates the fibre, propagating along the optical fibre for remote detection using a multi-pixel photon counter. The sensor demonstrates a high sensitivity to Iodine-125, the radioactive source most commonly used in brachytherapy. The sensor was initially tested for its response to 0.348mCi of Iodine-125. The sensor was further evaluated for its response to different levels of radiation to determine its suitability in comparison to previous work investigating terbium doped gadolinium oxysulphide (Gd2O2S:Tb).