The American Cancer Society says radiation therapy uses high-energy beams or particles to damage cancer cells and cause them to die or fail to divide and grow. Radiation therapy is delivered by a machine outside the body or by placing radioactive sources close to tumors. According to the Radiological Society of America, 50 to 60 percent of all cancer patients receive radiation as part of their treatment.
Function
High-energy radiation beams or particles work by damaging the DNA of cells, according to the National Cancer Institute. When cells divide they need to accurately duplicate the DNA so each of the two resulting cells has identical sets of genes. Radiation triggers errors in the duplication process, resulting in nonfunctional genes. Because one or both of these cells are unable to function or divide again, they die and are eliminated by the body shrinking the tumor. However, normal healthy cells often are also damaged in the process, causing a variety of side effects.
Uses
For some cancers radiation therapy is used in an attempt to cure the disease by eliminating the tumor. The Radiological Society lists head and neck cancers and prostate cancer as commonly treated in this way. The American Cancer Society also lists radiotherapy as a primary treatment for bladder and lung cancers and Hodgkin's disease. Radiotherapy is often used in combination with chemotherapy to increase the effectiveness in eliminating tumors. Radiotherapy is also used as a preventive treatment usually following a primary treatment, such as surgery, to prevent the cancer coming back. Palliative radiotherapy may be used to shrink tumors that have spread to other parts of the body, causing pain or interfering with normal functions such as eating or digestion.
External
The National Cancer Institute says radiation therapy delivered by a machine outside the body is most often in the form of photon beams or particle beams, such as x-rays. Other forms include electromagnetic radiation similar to microwaves. Many technologies have been developed to increase the intensity and precision of delivering radiotherapy. These include three-dimensional conformal radiation therapy, intensity modulated radiation therapy, image-guided radiation therapy, stereotactic radiosurgery, tomotherapy and proton therapy.
Internal
Internal radiotherapy, or brachytherapy, involves placing a tiny bit of radioactive material in or near the tumor, according to the National Cancer Institute. When placed inside the tumor it is called interstitial brachytherapy. When placed in the cavity surrounding a tumor that has been removed, it is called intracavitary brachytherapy. For some cancers, such as cancer of the eye, the radiation source is placed next to or close to the tumor, which is called episcleral brachytherapy. Systemic radiotherapy is another form of internal radiotherapy. This involves attaching a radioactive isotope to a monoclonal antibody engineered in the laboratory to seek out and attach to a particular protein characteristic of a tumor. The aim is to concentrate the radiation in the area of the cancer and spare normal tissues.
Side Effects
The National Cancer Institute says the side effects of radiotherapy can occur soon after treatment, called acute or early side effects, or can occur much longer after treatment, called late or chronic side effects. Depending on the part of the body being treated, common acute side effects include skin irritation, mouth sores, nausea, vomiting, urinary problems, hair loss and fatigue. Late or chronic side effects can include fibrosis, or residual scar tissue that interferes with normal function; bowel problems; memory loss; and infertility.
