Abstract
We discuss the physical aspects of the cancer treatment by the particle radiation therapy. First we discuss of the theoretical derivation of the flight length of charged particles such as heavy ion or pi-mesons. Secondly we estimate the effects of the strong interactions, taking the example of the meson mass. As a result, we conclude that the collision of Reighley scatterings of the charged particle with the electrons in the targets are important to determine the flight length, the relativistic effect should be included, and the effects of the strong interactions are also important in the absorption of the pion, which causes so-called star-formation.
