Biological effects of low-dose radiation are studied by computational methods. Assessing the risks of low-dose radiation, i.e. radiation-induced cancer, is becoming important in the study of public health because of the many different types of exposures, medical exposures, and from radiation protection viewpoints. In general, radiation effects arise from damage done to DNA by ionizing radiation. Therefore, examining effects from the initial DNA damage to the risk assessment is a problem with a very wide spatiotemporal scale. We are studying this problem by dividing it into three parts: 1) the DNA strand is broken by ionizing radiation, 2) DNA lesion repair, and 3) the process of cell carcinogenesis and tumorigenesis. In this paper, we mainly focus on the third part, the study of modeling and simulation of cell carcinogenesis.