ABSTRACT
High energy beams allow sparing of the skin overlying deep-seated tumors; fractionation of radiation dose decreases damage to skin and other normal tissues affected by the beam. This chapter discusses the radiation response in connection with cell-cycle phenomena and a review of methods used to represent them mathematically. Mathematical models of cell-cycle kinetics can be divided into two groups: nondynamic and dynamic. Different stationary models of the cell-cycle will be divided into three somewhat arbitrary classes. The average cycle and G1 durations vary significantly according to generation in a cultured cell population: a decrease during the first three generations after monolayer culture, and then an increase with the age of the culture. When the dose per fraction is small enough, the slope of the multifraction response curve approaches the initial slope of the single-dose survival curve, which is nonzero for the majority of mammalian cell and tissue dose-response curves available in the literature.
