Beam monitor for hadron therapy using a crystalline pixel detector

The unique dose deposition properties of hadron beams allow delivery of high dose to deep seated tumors while sparing surrounding normal tissue. Spot scanning techniques can achieve very high precision in targeting complex geometric shapes. In order to be able to distribute the dose exactly as planned, exact information about the incoming particle beam during the course of treatment is mandatory. Therefore a high resolution and high-speed beam monitor is needed. Silicon pixel detectors are very promising candidates for this task. They have a high spatial resolution and can be built very thin, in order to not disturb the beam. In the AD-4/ACE experiment at CERN, we test a new crystalline silicon pixel detector called MIMOTERA, applying a pulsed antiproton beam (3 x 107 particles per 500 ns every 90 seconds). We will show results of first measurements, examining sensitivity, temporal and spatial resolution, and linearity of the detector response with beam intensity. Next steps will include investigations of the detector response to beam energy and linear energy transfer for antiprotons, protons, and carbon ions.