Hit and target models for DNA damage with indirect action

Hit and target theory is widely known as a method for deriving the survival probability of a cell from the number of deoxyribonucleic acid (DNA) strand breaks. Direct action and indirect action are the way of causing DNA lesion by radiation. The object of a hit and target model is dried DNA. Strictly speaking, the model does not represent the generating mechanism of lesion in vivo. The biological effect by the direct action is major affection in a high dose region. However, the influence by the indirect action is major affection in a low-dose region. Topics of modern interest concerning radiation damage are becoming the affection in the low-dose region. In this paper, we propose enhancing hit and target models which take the indirect action into consideration.