It is considered a local therapy because the cancer cells are destroyed only in the anatomical area being treated. The radiation causes a breakage of one or both stands of the DNA molecule inside the cells, therefor preventing their ability to grow and divide. While cells in all phases of the cell cycle can be damaged by radiation, the lethal effect of radiation may not be apparent until after one or more cell divisions have occurred. Although normal cells can also be affected by ionizing radiation, they are usually better able to repair their DNA damage. Radiation treatments can be administered externally or internally, depending on the type and extent of the tumor, however only external radiation can be administered in an out-patient basis.
Some patients have both forms, one after the other.
X-rays, radioactive elements, and radioactive isotopes are most often used in these forms of treatment. External radiation treatments are administered by machines that deliver high-energy radiation. These machines vary according to the amount and type of energy produced. The kind of machine will differ depending on the type and extent of the tumor. Technological advances have permitted the development of machines with increased energy, allowing for precise page 5 treatments of deep seated tumors with less damage to superficial tissues.