Radiation therapy, which involves the use of high energy electromagnetic waves, is used to treat between 50–60% of cancers. The treatment is based on the fact that most cells are susceptible to radiation when they are dividing. The common side effects of radiation therapy are fatigue, nausea and some external burns to the skin, therefore the dose of radiation needs to be carefully calculated in order to give the optimum antitumor dose with minimal side effects.
Radiation treatment is delivered in one of two ways. With external beam therapy, the area is irradiated with X-rays from an external source. The dose of X-rays is given in short, fractionated daily doses over a period of time, a regimen known as continuous hyperfractionated radiotherapy ‘CHART’, to allow normal cells to recover. Treatment regimens depend on the size and location of the tumor and the purpose of the treatment, that is, whether it is intended to cure, to shrink the tumor prior to surgery or chemotherapy or to palliate an incurable tumor. With internal therapy the radioisotope is placed near or inside the tumor for a short period of time, a process known as brachytherapy. For example, intracavitary radiotherapy involves the insertion of 137Cesium into a body cavity in an applicator. This form of treatment is used for cancer of the vagina, cervix or uterus. Alternatively, thin radioactive wires may be inserted directly into the tumor, as, for example, in the treatment of prostate cancer. Internal therapy may also involve giving the patient a radioactive liquid either orally or intravenously. For example, a drink of radioactive iodine may be given to treat thyroid cancer. Since the thyroid preferentially takes up iodine , the radioactivity becomes concentrated at the site where it is required. Intravenous radioactive liquids are used to treat metastatic bone cancer.