Radiation therapy uses high-energy waves, such as x-rays, gamma rays, electron beams to destroy cancer cells. External radiation therapy is usually given with a machine called a linear accelerator (often called a “linac” for short).

Radiation can be given alone or used with other treatments, such as surgery or chemotherapy. In fact, certain drugs are known to be radiosensitizers. This means they can actually make the cancer cells more sensitive to radiation, which helps the radiation to better kill cancer cells.

Radiation therapy uses special equipment to send high doses of radiation to the cancer cells. Most cells in the body grow and divide to form new cells. But cancer cells grow and divide faster than many of the normal cells around them. Radiation works by making small breaks in the DNA inside cells. These breaks keep cancer cells from growing and dividing and often cause them to die. Nearby normal cells can also be affected by radiation, but most recover and go back to working the way they should.

Unlike chemotherapy, which exposes the whole body to cancer-fighting drugs, in most cases, radiation therapy is a local treatment. It’s aimed at and affects only the part of the body being treated. The goal of radiation treatment is to damage cancer cells, with as little harm as possible to nearby healthy cells.

Radiation beams are aimed very precisely. A special mold, mask, or cast of a body part may be made to help you stay still during treatment. These will also help get you in the same position for each treatment.

In most cases, the total dose of radiation needed to kill a tumor can’t be given all at once. This is because a dose of radiation given all at once can cause more damage to nearby normal tissues. This can cause more side effects than giving the same dose over many treatments.

The total dose of external radiation therapy is usually divided into smaller doses called fractions. The most common way to give it is daily, 5 days a week (Monday through Friday) for 5 to 8 weeks. Weekend rest breaks allow time for normal cells to recover.

External radiation is a lot like having a regular x-ray. The treatment itself is painless and takes only a few minutes. But each session can last 15 to 30 minutes because of the time it takes to set up the equipment and put the patient in position.

The patient is asked to lie on a treatment table next to the radiation machine (the linear accelerator or linac). The machine has a wide arm that extends over the table. The radiation comes out of this arm. The machine can move around the table to change the angle of the radiation if needed, but it won’t touch you.

External radiation therapy affects cells in your body only for a moment. Because there’s no radiation source in your body, you are not radioactive at any time during or after treatment.

Newer, more precise ways of giving external radiation therapy can help better focus the radiation and do less damage to normal tissues. This allows doctors to use higher doses of radiation.