A particle therapy system that is adapted to irradiate a target volume (1) with charged particles in compliance with a desired 3-D dose distribution. Such a desired 3-D dose distribution is achieved while delivering a plurality of particle energy distributions at the output of an energy-shaping device (10) crossed by an incident mono-energetic charged particle beam (6). The energy-shaping device comprises a plurality of groups (12, 22) of energy-shaping elements (11, 21), each of them comprising an individual layer of fluid or solid material (13), which thickness is adapted individually by a control unit (14). The use of configurable layers of fluids or solid materials makes the energy-shaping device reusable for treating different patients.