ABSTRACT
Combinations of cancer chemotherapeutic drugs and radiation treatment may provide a therapeutic gain by one of the four following mechanisms:
1. Enhancement of the tumor response in excess of the enhancement of normal tissue damage
2. Normal tissue protection if the tumor cells are not similarly protected 3. Toxicity independence 4. Spatial cooperation indicating that the two treatment modalities affect different tumor
sites
The possibility of normal tissue protection has, so far, not been investigated clinically and toxicity independence should generally not be expected. Thus, spatial cooperation and enhancement of the tumor response represent the modes of action which, practically, may lead to a therapeutic gain. In order to obtain such a therapeutic gain both in terms of spatial cooperation and by enhancement of tumor response, it is, however, crucial to avoid enhanced critical normal tissue damage since application of optimal treatment regimens would otherwise be impossible. Consequently, knowledge about drug-radiation interactions in critical normal tissues is one of the most important factors for the successful use of combined drugradiation regimens.
