Radiation therapy uses specific types of radiation to kill or shrink cancer cells. Radiation targets cancer cells and disrupts or destroys their genetic material, preventing the cells from continuing to grow and spread throughout the body.

There are several different types of radiation and methods of delivery, but they can be grouped in two categories:

• External  beam radiation. The most widely used method of targeting cancer cells with radiation, it uses precise radiation beams from a machine located outside the body. These beams are directed at the tumor or targeted site.
  
  
• Internal radiation (brachytherapy). The source of the radiation (e.g., “seeds,” wires) is given intravenously or by injection. Internal radiation methods include:
  
  
• Intracavitary radiotherapy. The radiation is placed inside an organ, such as the uterus.
  
  
• Interstitial radiotherapy. The radiation source is placed directly inside the tumor or tissue.
  
  
• Systemic radiation. Radioactive materials are delivered through the mouth or by injection and travel throughout the body.

Some radiation types penetrate the body deeply, while others can be more precisely controlled to treat a very small or targeted area. Radiation therapy is sometimes used alone to treat cancer. In other instances, it is combined with other cancer treatments, such as chemotherapy or surgery. Radiation may be used before or after surgery, depending on the type of cancer and the patient’s treatment plan.

While radiation therapy often is effective at treating and controlling cancer, it can damage normal cells that – like cancer cells – grow and divide rapidly. While this damage usually is temporary, it can cause serious side effects for some patients. The potential side effects vary with the type and amount of radiation received and the area being treated.

A patient’s radiation therapy plan will depend on the goal of the treatment, such as shrinking a tumor or destroying any remaining cancer cells. The patient’s general health, tolerance for radiation and goals are considered when balancing the risks of radiation therapy with the potential benefits.