Organizational response of normal tissues to irradiation

A central tenet in the treatment of cancer patients with radiation has been that normal tissue complications were related to the volume of the tissue irradiated, although the mechanisms underlying this phenomenon were poorly understood. The advent of new treatment techniques, such as three-dimensional (3-D) conformal treatments, drove the developers of models to evaluate the resultant complex dose distribution plans, particularly in terms of predicting normal tissue complications. However, a lack of experimental data on the effects of changing volume on normal tissue responses made it difficult to substantiate these models. Consequently, radiobiology research on normal tissue dose volume effects in experimental animal models was initiated, providing considerable insight into the effect of changing volume on normal tissue response for a large number of tissues. This paper summarizes these data and the potential impact of new concepts and data in molecular radiation biology on dose volume effects in normal tissues.