Radiogenic responses of normal tissue induced by fractionated irradiation -a simulation study. Pt. 1. Acute effects

Based on control theory, the attempt is made in this paper to construct a computer model which describes the time course of fast proliferating normal tissue after irradiation treatment. Subsequently, different clinical irradiation schems are compared in regard to their radiogenic acute effects. A cybernetic model of a cell renewal system consisting of stem-, transit- und functional cells has been developed and transferred into a computer model. The radiation effects are considered by characteristic cell parameters as well a by the linear-quadratic model. Three kinds of tissue (thick epidermis of man, thin epidermis of the mouse and jejunum of the mouse) have been irradiated in the model in accordance with different clinical irradiation schemes (standard-, super-, hyperfractionation and a single high dose per week). The simulation studies demonstrate that the acute reaction of normal tissue to hyperfractionation (3 times 1.5 Gy per day) is particularly severe. Furthermore, the radiation damage of the jejunum and of the thin epidermis of the mouse depends on the specific irradiation scheme and is only partially compensated. A comparison of the simulation results with clinical experience (and practice) demonstrates that the clinical reality can in quality be successfully represented by the model. This opens the door for connecting the side effects of irradiation to normal tissue with the corresponding tumor effectiveness. (orig.)