Understanding Radiation Therapy 

More than half of all people with cancer are treated with radiation therapy, a type of cancer treatment that is used to shrink tumors and stop the growth of cancer cells. Radiation therapy uses ionizing radiation to kill cancer cells and shrink tumors. Radiation therapy may be external or internal. External radiation, the type most often used, comes from a machine outside the body, and is usually given on an outpatient basis. Internal radiation is implanted into or near the tumor in small capsules or other containers. It may require a hospital stay.

What is Radiation Therapy?

Radiation therapy is the use of a certain type of energy – called ionizing radiation – to attack and kill cancer cells and ultimately shrink tumors. Radiation therapy injures or destroys cells in the area being treated, also know as the “target tissue”, by damaging their genetic material, impeding the cancer cell’s ability to continue to grow and divide.

Although radiation damages both cancer cells and normal cells, typically most normal cells can recover from the effects of radiation and function properly. The goal of radiation therapy is to damage as many cancer cells as possible, while limiting harm to nearby healthy tissue.

How Does Radiation Therapy Work?

There are different types of radiation and different ways to deliver the radiation. For example, certain types of radiation can penetrate more deeply into the body than can others. In addition, some types of radiation can be very finely controlled to treat only a small area (an inch of tissue, for example) without damaging nearby tissues and organs. Other types of radiation are better for treating larger areas.

In some cases, the goal of radiation treatment is the complete destruction of an entire tumor. In other cases, the aim is to shrink a tumor and relieve symptoms. In either case, doctors plan treatment to spare as much healthy tissue as possible.

About half of all cancer patients receive some type of radiation therapy. Radiation therapy may be used alone or in combination with other cancer treatments, such as chemotherapy or surgery. In some cases, a patient may receive more than one type of radiation therapy.

Radiation therapy uses a special kind of high-energy beam to damage cancer cells. (Other types of energy beams include light and X-rays.) These high-energy beams, which are invisible to the human eye, damage a cell’s DNA, the material that cells use to divide.

Over time, the radiation damages cells that are in the path of its beam — normal cells as well as cancer cells. But radiation affects cancer cells more than normal cells. Cancer cells are very busy growing and multiplying — two activities that can be slowed or stopped by radiation damage. And because cancer cells are less organized than healthy cells, it's harder for them to repair the damage done by radiation. So cancer cells are more easily destroyed by radiation, while healthy, normal cells are better able to repair themselves and survive the treatment.

There are two different ways to deliver radiation to the tissues to be treated:

• a machine called a linear accelerator that delivers radiation from outside the body
• pellets, or seeds, of material that give off radiation beams from inside the body

Some people may fear radiation therapy. They may worry that therapeutic radiation may be dangerous like an atomic bomb or nuclear power plant. Stories about radiation side effects, some of them exaggerated, can circulate around hospital waiting rooms. It's important for you to know that there is NO connection between therapeutic radiation and the types of radiation in bombs and nuclear reactors. The radiation used in cancer treatment is highly focused, controllable, and generally safe.

What Are Possible Side Effects of Radiation Therapy?

Normal body tissues vary in their response to radiation. As with tumors, normal tissues in which cells are quickly dividing may be affected. This causes some of the side effects of radiation treatment. Since radiation is a local treatment, many side effects depend on the area of the body being treated. The early effects of radiation may be seen a few days or weeks after treatments have started and may go on for several weeks after treatments have ended. Other effects may not show up until months, or even years, later.

The major side effects are:

• Fatigue
• Skin changes
• Mouth and throat problems

There is the potential for additional side effects based on where you are receiving the radiation therapy.