Abstract Brachytherapy is a radiotherapy procedure performed with radioactive sources implanted into the patient's body, close to the area affected by cancer. This is a reference procedure for the treatment of prostate and gynecologic cancer due to the reduction of the dose released close to organs at risk (e.g., rectum, bladder, colon). For this reason, real-time dose verification and source localisation are essential for an optimal treatment plan. The ORIGIN collaboration aims to achieve this goal through a 16-fibre sensor system, designed to house a small volume of scintillating material in a transparent fibre tip to enable point-like measurements. The selected scintillating materials feature a decay time of about 500 μs and the signal associated with the primary γ -ray interaction results in the emission of a sequence of single photons distributed over time. Therefore, the dosimeter requires a detector with single-photon sensitivity and a system designed to provide dose measurements by photon counting. Uniformity of fibre response, system stability and reproducibility of measurements are key features of the dosimeter. The characterisation of the 16-channel dosimeter system equipped with thermo-electrically cooled Silicon Photomultipliers, carried out in the laboratory using an X-ray cabinet, is discussed and the results are compared with an earlier version equipped with SiPMs operated at room temperature.