Interposing a programmable path length of one or more materials into a particle beam modulates scattering angle and beam range in a predetermined manner to create a predetermined spread out Bragg peak at a predetermined range. Materials can be "low Z" and "high Z" materials that include fluids. A charged particle beam scatterer/range modulator can comprise a fluid reservoir having opposing walls in a particle beam path and a drive to adjust the distance between the walls of the fluid reservoir under control by a programmable controller. A "high Z" and, independently, a "low Z" reservoir, arranged in series, can be used. When used for radiation treatment, the beam can be monitored by measuring beam intensity, and the programmable controller can adjust the distance between the opposing walls of the "high Z" reservoir and, independently, the distance between the opposing walls of the "low Z" reservoir according to a predetermined relationship to integral beam intensity. Beam scattering and modulation can be done continuously and dynamically during a treatment in order to deposit dose in a target volume in a predetermined three dimensional distribution.