Radiation therapy is one of several options available to those diagnosed with cancer. Otherwise known as radiotherapy or irradiation, the technique is often used by doctors to reduce the size of tumors prior to surgery, but can also be used post-surgery to reduce the probability of relapse. Radiation therapy is considered a local treatment since it can be focused on a specific area, such as a cancerous growth in the lung or breast. However, since it is so precise, cancerous cells outside of the treatment area can be missed.

The treatment works by applying radiation to a location in the body. The radiation reacts with the cells in that location causing damage to their DNA. Cancerous cells consequently die because they lack the ability to repair the radiation damage. The damage results in permanent errors in the genetic code that cause the cells to destroy themselves rather than replicate. Healthy cells, on the other hand, maintain their ability to repair the radiation damage, and therefore are more often able to survive the bouts of radiation therapy.

There are two forms of radiation therapy used by doctors in the treatment of cancers: external and internal. External radiation therapy consists of high energy rays of radiation that are focused on the area receiving treatment. Internal radiation therapy is also known as brachytherapy. In this method, radioactive substances are placed inside the body at the site of the tumor. A radiation oncologist will determine the exact course of therapy to be used in a person’s treatment based upon the type of cancer, its location, and the patient’s personal medical history.

There are several methods of external radiation therapy available today. Most commonly, a machine called a linear accelerator is used to create high energy rays of sub-atomic particles. High doses of x-rays, electron beams, or gamma rays from radioactive cobalt are also regularly used in treatment. Newer treatments are also becoming more widely available.

Research has led to the development of radiation treatments that are much more accurate than older methods, affecting only the tumor and not healthy surrounding tissues. Among the newest techniques are Three-dimensional Conformal Radiation Therapy, Stereotactic Radiotherapy, Cyberknife, the Peacock System, and Precision Therapy. Most of these methods rely on imaging of the tumor area and specifically delivered doses of radiation coming from many different angles of attack.

External radiation therapy only affects the person receiving the radiation. However, the patient will not become radioactive from receiving radiotherapy! Patients of radiotherapy can have close contact with other people without worrying about transferring radiation. Side effects are usually minimal, but can include fatigue, decreases in blood cell counts, and irritation of the skin at the point of radiation. The side effects experienced are usually specific to the areas being treated. For example, if the abdomen or stomach receives radiation, nausea and vomiting should be expected.

Internal radiation therapy is preferred by doctors if they wish to deliver a high dose of radiation in a short period of time, and can be used in conjunction with external radiation. The implants are often referred to as seeds or capsules. They can be placed directly into the tumor or near a tumor in a body cavity. This procedure is surgical in nature, and must therefore be performed under some form of anesthesia in a hospital. In addition, the radiation being implanted can be released from the body. So, patients receiving internal radiation therapy are often isolated in their hospital room, and allowed visitors on a limited basis for the duration of treatment. As with external radiation therapy the side effects are minimal, and depend generally on the location of the radioactive implant.

Kirsten Sanford is a science journalist & PhD candidate in the Molecular, Cellular and Integrative Physiology Graduate Group at the University of California, Davis. In addition to developing patient health education materials she also hosts a weekly science radio show (This Week in Science) dedicated to bringing current scientific news and research to the public.