A radiation therapy system includes an accelerator and beam transport system that generates a beam of particles. The accelerator and beam transport system guides the beam on a path and into a nozzle that can aim the beam toward an object. The nozzle includes a beam energy adjuster that can adjust the beam by, for example, placing different thicknesses of material in the path of the beam to affect the energies of the particles in the beam to deliver a dose to the object with a Spread Out Bragg Peak.
