An innovative multichannel fibre-coupled Optically Stimulated Luminescence (OSL) dosimeter is proposed for on-line in vivo quality assurance in Radiation Therapy (RT). Small Al2O3 :C fibre crystals (TLD500) are used as OSL detectors, incorporated into a rugged, radiation-resistant and radiation-transparent OSL fibre sensor design. The temperature and fading dependences of OSL fibre sensors and stability vs cumulated dose have been tested with a X-ray generator. Predosed OSL sensors tested at Institut Gustave Roussy (IGR) show a good repeatability in multichannel operation. Sensor calibration and depth-dose measurements with electron beams have been performed with a Saturne 43 LINAC in reference conditions at CEA-LNHB (ionizing radiation reference laboratory in France). The difference between absorbed doses measured by OSL and an ionization chamber was within ± 0.9 % (for a dose of about 1 Gy) despite a sublinear dose response. Finally, a single calibration curve was used for all beams as energy independence vs electron energy was found in the range [9 MeV, 18 MeV]. Angular independence was found as well in the range [0°, 45°] when the OSL sensor is equipped with its bolus.