[en] The neutrontherapy program at Louvain-la-Neuve is carried out with the cyclotron CYCLONE of the Catholic University. This isochronous variable energy cyclotron, produced by CSF (Corbeville, France), accelerates different types of charged particles; in particular, deuterons can be accelerated at energies ranging from 13 to 50 MeV. Neutrons used for therapeutic applications are produced by bombarding a thick (10 mm) water cooled, Beryllium target with 50 MeV deuterons. A beam current of about 5 μA is used for patient treatments, which produces dose rates of about 0,5 Gy/min at a target-skin-distance (TSD) of 157 cm. The treatment room, and related medical facilities, are located one level below the main level of the cyclotron. This permits the use of a vertical therapeutic neutron beam by bending the deuteron beam at 90⁰. This vertical beam appears to be more adequate for positioning the majority of the patients. The collimation system consists of a fixed shielding and of a series of interchangeable inserts. The inserts are cylindrical in shape; their height is 80 cm and their external diameter 40 cm. The proximal part (50 cm) is a mixture of iron (equivalent thickness 22 cm) and epoxy, and the distal part (30 cm) is a mixture (50%) of borax and epoxy. The emphasis is made on the radioprotection conditions. A series of measurements made in the treatment room and in the entry maze have shown that their special configuration provides a satisfactory protection of the staff. (author)