Systems and methods of controlling a proton beam in a proton therapy system, the system including a proton beam delivery system including at least one achromatic beamline having a first power setting to direct a proton beam having a first predetermined range of proton beam energies to a target treatment area, and a second power setting to direct a proton beam having a second predetermined range of proton beam energies to the target treatment area, and a power changing unit configured to control an energy level of the proton beam and a power setting of the at least one achromatic beamline such that the power changing unit changes the power setting of the at least one achromatic beamline between the first power setting and the second power setting based on changes in proton beam energy that occur within the first predetermined range of proton beam energies.
