A radiation therapy system comprising: a cyclotron configured to output a charged particle beam ; and a beam energy modulation apparatus configured to receive said charged particle beam from said cyclotron ; wherein the beam energy modulation apparatus comprises a beam decelerating apparatus and a beam accelerating apparatus ; characterized in that : a set of switching dipoles is coupled with the cyclotron in order to receive the charged particle beam and direct the charged particle beam to either the input of the beam accelerating apparatus or the input of the beam decelerating apparatus ; said beam decelerating apparatus is configured to receive and decelerate said charged particle beam to produce a reduced energy charged particle beam, and said beam accelerating apparatus is configured to receive and accelerate said charged particle beam to produce an increased energy charged particle beam; and said beam decelerating apparatus and said beam accelerating apparatus each comprises a radio frequency structure; wherein the system further comprises a set of switching dipoles coupled with an output of the beam accelerating apparatus and an output of the beam decelerating apparatus and is configured to receive and direct the modulated energy charged particle beam . a cyclotron configured to output a charged particle beam ; and a beam energy modulation apparatus configured to receive said charged particle beam from said cyclotron ; wherein the beam energy modulation apparatus comprises a beam decelerating apparatus and a beam accelerating apparatus ; characterized in that : a set of switching dipoles is coupled with the cyclotron in order to receive the charged particle beam and direct the charged particle beam to either the input of the beam accelerating apparatus or the input of the beam decelerating apparatus ; said beam decelerating apparatus is configured to receive and decelerate said charged particle beam to produce a reduced energy charged particle beam, and said beam accelerating apparatus is configured to receive and accelerate said charged particle beam to produce an increased energy charged particle beam; and said beam decelerating apparatus and said beam accelerating apparatus each comprises a radio frequency structure; a set of switching dipoles is coupled with the cyclotron in order to receive the charged particle beam and direct the charged particle beam to either the input of the beam accelerating apparatus or the input of the beam decelerating apparatus ; said beam decelerating apparatus is configured to receive and decelerate said charged particle beam to produce a reduced energy charged particle beam, and said beam accelerating apparatus is configured to receive and accelerate said charged particle beam to produce an increased energy charged particle beam; and said beam decelerating apparatus and said beam accelerating apparatus each comprises a radio frequency structure; wherein the system further comprises a set of switching dipoles coupled with an output of the beam accelerating apparatus and an output of the beam decelerating apparatus and is configured to receive and direct the modulated energy charged particle beam . <EOS>