Biological effect of radiotherapy on cancer cells

Radiation therapy is a mainstay for curative treatment of many types of tumours. The cure rate of radiation therapy depends on its ability to induce non-repairable DNA damage leading to cellular death or loss of proliferative capacity. In addition to clinical factors, efficacy of radiation therapy has been explained by the radiobiological concept of 4R parameters summarized by Rodney Withers in 1975, which include Repair of DNA damage, Repopulation, Redistribution of tumour cells in the cell cycle, and Reoxygenation. This chapter reviews the direct and indirect effects of irradiation on cancer cells, mechanisms of DNA repair and radiation-induced cell death, and also discusses implementation of the cancer stem cell model for the radiobiological concept of tumour radioresistance.