Radiotherapy treatments become more and more accurate, using techniques like IMRT. Their irradiation fields and dose depositions are small and complex, and only a few dosimeters are available for real time and in vivo control for photons as well as for electrons beams. In this context, a new scintillating fiber dosimeter (SFD) has been developed by the "Laboratoire de Physique Corpusculaire de Caen", LPC Caen (France) in collaboration with one of the French regional center for cancer treatment, "Centre regional de lutte contre cancer F.Baclesse" CRLCC F. Baclesse in Caen, and the ELDIM Company in Herouville (France). This plastic dosimeter is water equivalent, and it is suitable for photons as well as for electrons beams without correction. It is a real time dosimeter, with an excellent signal to noise ratio, and a spatial resolution of about a few millimeters. Recently, a new light collection device has been developed to improve the spatial resolution to 1 mm without loss in the signal to noise ratio. The accuracy of this improved prototype has been tested by comparison with standard ionization chambers and the difference between the two devices never exceeded one percent for photon and for electron irradiation beams. A first set of commercial SFD is under completion at ELDIM and it will be soon clinically tested in several French centers for cancer treatment.