  Particle therapy is a well established clinical treatment of tumors. More
than one hundred particle therapy centers are in operation world wide. The
advantage of using hadrons like protons or carbon ions as particles for tumor
irradiation is the distinct peak in the depth dependent energy deposition,
which can be exploited to accurately deposit dose in the tumor cells. To
guarantee this, high accuracy of monitoring and control of the particle beam is
of utmost importance. Before the particle beam enters the patient, it traverses
a monitoring system which has to give fast feedback to the beam control system
on position and dose rate of the beam while minimally interacting with the
beam. The multi-wire chambers mostly used as beam position monitor have their
limitations when fast response time is required (drift time). Future
developments like MRI-guided ion beam therapy pose additional challenges for
the beam monitoring system like tolerance of magnetic fields and acoustic noise
(vibrations). Solid-state detectors promise to overcome these limitations and
the higher resolution they offer can create additional benefits. This article
presents the evaluation of an HV-CMOS detector for beam monitoring, provides
results from feasibility studies in a therapeutic beam and summarizes the
concepts towards the final large-scale assembly and readout system.
