Radiotherapy remains a mainstay in the treatment of cancer. Comparison of the contribution towards cure by the major cancer treatment modalities shows that of those cured, 49% are cured by surgery, 40% by radiotherapy and 11% by chemotherapy. Many more patients may benefit from radiotherapy to enhance quality of life through palliation of symptoms of recurrent or metastatic disease.

Definition

Radiotherapy is the use of ionizing radiation to treat disease. Ionizing radiation may be delivered by X-ray beams, beams of ionizing particles such as electrons, or by beta or gamma irradiation produced by the decay of radioactive isotopes.

Biological action of ionizing radiation

Ionizing radiation causes damage to cellular DNA both directly, and indirectly through toxic free radicals produced when radiation interacts with water within the cell. Rapidly proliferating cells are particularly sensitive to this damage. This leads to single and double DNA-strand breakage and unless repaired, causes reproductive death of the cell. Ionizing radiation can also cause DNA base mutation, and a risk of late carcinogenesis; an important consideration in the treatment of children, young adults and benign diseases with radiation.

External beam radiotherapy: X-rays, gamma-rays (clinically equivalent to X-rays but produced by radionuclide decay) or electrons emitted from an external source are incident on the skin and deposit energy either superficially or more deeply, depending on the characteristics of the beam. High-energy, penetrating therapeutic X-ray beams (and electrons) are typically produced by megavoltage linear accelerators. This complex equipment is located in radiotherapy departments, housed in bunkers to minimize radiation exposure to staff when the machine is activated.