ABSTRACT
Radiotherapy protons interact with matter in few ways. Absorbed dose is the energy per unit mass deposited by the beam in the stopping medium. Most radiotherapy protons traversing matter slow down and eventually stop by myriad soft EM collisions with atomic electrons. The present section concerns the continuous slowing down approximation (CSDA) theory of this process, range-energy tables, and some consequences for proton radiotherapy calculations. A beam monitor is followed by a variable-thickness column of the material under test. The protons stop in a Faraday cup (FC) which measures total charge, acting as a proton counter. In the general physics literature, such as range-energy tables, “range” means precisely the quantity defined earlier, namely the depth at which half the surviving primaries have stopped. Compounds are more complicated since their constituent atoms are bound in molecules and do not, strictly speaking, act separately.
