Along with surgery and chemotherapy, radiation therapy (radiotherapy) is one of the most important methods of cancer treatment. At least 50 percent of all cancer patients will receive radiotherapy at some stage during the course of their illness. It is currently used to treat localized solid tumors, such as cancers of the skin, brain, breast, or cervix, and can also be used to treat leukemia and lymphoma (Tobias JS 1992).

Most types of radiation do not attack cancer cells specifically, and therefore cause injury to normal tissues surrounding the tumor. The adverse effects are a major factor limiting the success of radiation treatment. However, proton therapy and CyberKnife® therapy are technologically advanced forms of radiotherapy that cause little damage to normal tissue because they focus intensely on the tumor.

The effectiveness of radiation therapy can be enhanced by both radiosensitizers, such as genistein, curcumin, green tea, and hyperthermia, and radioprotectors, such as ginseng, glutathione, whey protein, and shark liver oil. Overall, the use of specific nutritional supplements, drugs, and other strategies may prevent and help to alleviate and treat the side effects caused by radiation, and thereby improve the effectiveness of radiotherapy.

Principles of Radiation Therapy (Radiotherapy)

Radiation therapy is the treatment of cancer with ionizing radiation. Radiation works by damaging the DNA (genetic material) within the tumor cells, making them unable to divide and grow. Radiation is often given with the intent of destroying the tumor and curing the disease (curative treatment). However, although radiation is directed at the tumor, it is inevitable that the normal, non-cancerous tissues surrounding the tumor will also be affected by the radiation and therefore damaged (Burnet NG et al. 1996). The goal of radiation therapy is to maximize the dose to tumor cells while minimizing exposure to normal, healthy cells (Emami B et al. 1991).

Because no single therapy can provide complete treatment for a patient with a solid tumor, radiotherapy is often used in combination with surgery or chemotherapy to improve the chances of a successful treatment outcome. Sometimes radiation is used to relieve symptoms, such as pain or seizures; this is called palliative treatment (Hoskin PJ et al. 1992).

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).