A method for beam therapy is provided. The method includes receiving first data indicating a plurality of target volumes within a target region inside a subject for particle beam therapy relative to a particle beam outlet on a gantry for directing a particle beam from a particle beam source. The method further includes moving automatically, one or more energy modulator components to reduce an energy of the particle beam and deliver the particle beam to the target region such that a Bragg Peak is delivered to at least one target volume of the plurality of target volumes. The method further includes repeating the moving automatically as the particle beam source rotates with the gantry around the subject, without changing the energy of the particle beam at the particle beam outlet, until every target volume is subjected to a Bragg Peak.
