Transmission improvement options via local energy degradation at a cyclotron driven ocular tumor treatment facility

The goal of this work is to increase the beam transmission from the cyclotron to the patient location of ocular tumor treatment facility Optis 2 at the Paul Scherrer Institute and thus to reduce the patient treatment times. The examined options for such transmission increase were the installation of local degraders in the patient treatment room and modification of the energy selection collimator settings. The experiments have shown that an improvement of the beam transmission is possible to achieve, however on a cost of an increase in lateral or distal penumbra of the beam. The benefits and drawbacks of the examined options are discussed.