The Proteus C-235 cyclotron was designed and produced by IBA (Ion Beam Applications S.A., Belgium) specifically for medical applications. It is an isochronous cyclotron with a compact conventional magnet, able to accelerate protons to an energy of 230 MeV. Protons of this energy have a range of some 30 cm in water which and are thus able to reach all tumour locations in a radiotherapy patient. An energy degrader and selector, allowing the beam energy to be downgraded continuously to 70 MeV, with intensities up to 600 nA, is an integral part of this installation. The Proteus C-235 cyclotron with its energy selector was installed in its new building at IFJ PAN on May 11, 2012. The rotating arm (gantry) has also been installed and is currently undergoing completion.