ABSTRACT
Radiation-induced neoplasms cannot be distinguished from those that occur spontaneously or that are induced by chemical carcinogens. The structural and functional changes in carcinogenesis may be similar irrespective of causative agents. Cancer cells result from accumulation of multiple genetic changes in normal dividing cells, which occur over a long period of time. The latent period (time interval between exposure to carcinogens and detection of cancer) of a neoplasm depends upon the radiation dose, type of organ exposed, and experimental models (tissue culture, animals, or humans). Three models are used to study radiation carcinogenesis: the tissue culture model, the animal model, and the human model. The latent period for radiation-induced cancer is about a few weeks in the tissue culture model, about a few months in the animal model, and several years in the human model. In addition to cancer, irradiation can also increase the risk of nonneoplastic diseases. At present, there are no effective preventive strategies to reduce the risk of either radiation-induced cancer or nonneoplastic diseases. Before discussing the studies on radiation-induced cancer using each experimental model, it is important to understand the incidence of spontaneous cancer per year in order to evaluate the impact of radiation-induced increases in the incidence of cancer on society in terms of cost and well-being.
