[Therapeutic ratio in combined radio-chemotherapy--radiobiological considerations]

Although much effort has been directed for obtaining a more effective way of combination in combined radio-chemotherapy, radiobiological rationales for improving the therapeutic ratio have not yet been established. Biological characteristics of solid tumors, target normal tissues in acute and chronic injuries, and also their implications in radio-chemotherapy were discussed in this review. These include cellular kinetics, pH gradient and 4 R's during the treatment course. It was considered that experimental model systems in vitro suitable for solid tumors and slowly proliferating normal tissues are required for obtaining rationales to improve therapeutic ratio.