Some embodiments of the present invention provide apparatus having a particle beamline for passage of charged particles of radiation therealong, comprising: a first beam tracker structure comprising at least one position sensitive detector (PSD) for determining a location with respect to a cross-sectional area of the beam line at which particles pass through the PSD； energy discrimination apparatus for determining an energy of particles that have passed through the first beam tracker structure； and support means for supporting a subject in a path of a particle along the beamline between the first beam tracker structure and the energy discrimination apparatus, the apparatus being configured to be operated in a selected one of a first mode and a second mode, the apparatus being configured, in the first mode of operation, to control an energy of the beam of charged particles passing through the first beam tracker structure such that a Bragg peak of charged particle absorption is located within the subject, and in the second mode of operation, to control an energy of the beam of charged particles passing through the first beam tracker structure such that a Bragg peak of charged particle absorption is located within the energy discrimination apparatus.
