A particle beam therapy system including an accelerator for making a beam of charged particles available, a beam guiding unit supplying the beam to a treatment location starting from the accelerator, and at least one beam property monitor arranged along the beam path. A control unit communicates with the beam property monitor and guiding unit and determines deviations of actual properties from desired properties of the beam and transmits control signals for adapting the beam properties to the guiding unit, using said deviations. Precise beam guidance is achieved by arranging the beam property monitor on the periphery of the beam perpendicular to the beam path such that the beam properties are detected due to their direct interaction with particles of the beam in the halo region and/or indirectly by electromagnetic interaction. A method for a beam of charged particles in a particle beam therapy system is also disclosed.