Fundamental limits to stereotactic proton therapy

Proton therapy treatment techniques continue their steady development from passive scattering to 3-D multi-field scanning modalities. As the demands for faster and more accurate treatment increase, the requirements and tolerances on beam delivery technologies become more stringent. Fundamental physical limits (energy straggling and multiple Coulomb scattering) ultimately limit treatment performance parameters, even for an ideal accelerator and nozzle system. This paper calculates how few independent beam delivery control points are needed in a tumor in order to perform the sharpest possible stereotactic surgery, with 1% integrated dose flatness.