Application of heavy ion plasma to understand treatment mechanism of heavy ion cancer therapy

Over one century passes since plasma is thought to be produced in swift heavy ion irradiation, theoretically. However, it is still unclear if this irradiation forms plasma or not. The problem of the presence or the absence of the plasm is important to estimate the radial dose distribution because the presence of plasma increases radial dose, that is, decreases this rate. Here, the radial dose is the dose as a function of the distance from the incident ion path and is employed in the treatment planning system for the cancer therapy to estimate the survival rate of cells. To study this plasma, we developed a new simulation model as follows. In heavy ion irradiation, huge number of molecules are ionized along the path of the incident ion. We expect the molecular ions produced here to form strong electric field. We incorporated the effect of this electric field on the motion of secondary electrons in our model.Not that there is a measurement of the secondary electron yield that indicated that this electric field traps the motion of secondary electrons. These trapped secondary electrons are expected to form plasma. Only our simulations almost reproduce the trend of this measurement. Using plasma theory, We derived a new formulation which almost reproduced our simulations.