Compact proton beam energy modulator

A proton beam imaging system comprising:

• a proton beam generator to generate a proton beam;
• a proton beam modulator through which the proton beam passes positioned between the proton beam generator and an image target;
• and
• a proton beam detector positioned to detect the proton beam exiting the image target;
• wherein the proton beam modulator comprises:
• a rotating wheel having an axis of rotation positioned so that the proton beam passes through the axis of rotation and the axis of rotation is perpendicular to the proton beam;
• a first modulating portion comprising a first material portion and a second material portion through which a proton beam passes;
• and
• a second modulating portion comprising a third material portion and a fourth material portion through with the proton beam passes;
• wherein the first and second modulation portions are positioned opposite each other on the rotating wheel,
• wherein the first, second, third, and fourth material portions comprise a wedge shape having a varying thickness to modulate an energy level of the proton beam as the proton beam modulator rotates, wherein the proton beam is modulated to have a substantially constant degree of scattering as the proton beam modulator rotates.