Cancer Radiation Therapy
What is Ionizing Radiation?
Radiation used for cancer treatment is called ionizing radiation because it forms ions as it passes through a tissue. Ions are atoms that have acquired an electric charge through the gain or loss of an electron (Dunne-Daly CF 1999). Ions can cause cell death or genetic change either directly or indirectly. The direct effect causes a change in the molecular structure of biologically important molecules, most likely DNA. The indirect action of radiation occurs when it interacts with water molecules in the cells, resulting in the production of highly reactive and unstable free radicals or reactive oxygen species, which immediately react with any biomolecules in the surrounding area, producing cellular damage (Fang YZ et al. 2002).
This damage can lead to cell death by two mechanisms (Ross GM 1999). The first process, known as apoptosis, results in cell death within a few hours of radiation (Kerr JF et al. 1994). The second mechanism is radiation-induced failure of cell division and the inhibition of cellular proliferation, which in turn leads to cell death. Several enzymatic and nonenzymatic antioxidant defense mechanisms exist in cells and prevent excessive damage through the scavenging and inactivation of these reactive oxygen species (Mates JM et al. 2000).