Cell and Tissue Kinetics

Abstract

The response of cells to low LET radiation is often dependent upon phase of the cell cycle at the time of irradiation, but the response of tumors and normal tissue is dependent on other additional parameters such as growth fraction and cell loss. G2/M phase cells are most radiosensitive, while late S-phase cells are most radioresistant. The cell cycle can stop at various checkpoints if DNA damage is detected; progression of cells into S phase or mitosis is usually delayed in normal cells if DNA is damaged. Flow cytometry can be used to measure the proportion of cells in various phases of the cell cycle. This may be used to calculate cell cycle time, growth fraction, cell loss factor, doubling time and potential doubling time of tumors. Cell repopulation can counteract cell killing during a prolonged course of radiotherapy. On the other hand, redistribution allows cells to progress to a more sensitive phase of the cell cycle, increasing cell killing after administration of subsequent fractions of IR.