Fundamental limits to stereotactic proton therapy

Proton therapy techniques are developing from passive scattering toward 3-D multifield scanning modalities, increasing the demands for speed and for dose distributions with sharp edges. Fundamental physics (energy straggling and multiple Coulomb scattering) ultimately limit treatment performance parameters, even for an ideal beam delivery 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.