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External Radiation Therapy


For a person with cancer, radiation therapy is often part of the treatment plan. If you or a loved one needs radiation therapy for cancer treatment, a radiation oncologist will decide whether external or internal beam radiation therapy is the right option.

External radiation therapy, also called external-beam therapy (EBT), refers to a treatment that uses beams of radiation delivered from a machine outside the body to precisely target a tumor. In contrast, internal-beam radiation—also called brachytherapy—uses radioactive implants, such as seed implants, placed inside the body near a tumor to deliver radiation locally.

External radiation therapy is used to treat a wide variety of cancers, including skin lymphoma, breast, colorectal, esophageal, head and neck, lung, brain tumor and prostate cancers. If you are scheduled to have external beam radiation therapy, you might wonder what to expect and want to learn more about what’s involved in the treatment.

“The radiation used in external beam radiation therapy can come from a variety of sources,” says Yale Medicine’s Lynn Wilson, MD, vice chair and clinical director of the Department of Therapeutic Radiology. “Your doctor may choose to use X-rays, an electron beam or cobalt-60 gamma rays.”

At Yale Medicine, we have highly specialized radiation oncologists who focus on treating one kind of cancer. They work alongside highly trained physicists to ensure radiation therapy is delivered precisely where it will be most effective in treating cancer.

How will my radiation oncologist know how much radiation to use?

The choice of which type of radiation to use will be made by your radiation oncologist, depending on what type of cancer you have and on how deep into your body the doctor wants the radiation to penetrate. High-energy radiation is used to treat many types of cancer. Low-energy X-rays are used to treat some kinds of skin diseases.

How does the radiation oncologist know where to deliver radiation therapy?

After a physical exam and a review of your medical history, the radiation oncologist plans treatment to pinpoint exactly where the radiation should be directed. 

In a process called simulation, you will be asked to lie very still on a table while the radiation therapist uses a special X-ray machine to define your treatment port or field. This is the exact place on your body where the treatment will be aimed. You may have more than one treatment port. Simulation may take from a half hour to about 2 hours.

The radiation therapist often will mark the treatment port on your skin with tiny dots of colored, semi-permanent ink to outline the treatment area. The treatment marks need to remain visible until your treatment is complete, so you will need to be careful when you bathe or shower. 

If they start to fade, you will need to tell the therapist who can darken them to ensure they remain visible. Do not try to draw over faded lines at home unless they will be completely gone before your next visit. If you do replace the marks, be sure to tell the therapist at your next visit!

Using the information from the simulation, along with other test results and information about your medical history, your doctor, the radiation physicist and the dosimetrist (all highly trained experts) will collaborate to determine where to precisely deliver treatment.

Your doctor then decides how much radiation is needed, how it will be delivered, and how many treatments you should have. This process often takes several days and results in a personalized treatment plan for you.

How long does treatment take?

Radiation therapy usually is given several days a week for up to seven weeks, depending on the patient's individual treatment plan. When radiation is used for palliative care, the course of treatment can last from one day to three weeks. An advantage of this type of schedule—which uses daily radiation in small amounts instead of fewer, larger doses—is that it helps protect other tissues from the harmful effects of radiation. Weekend rest breaks allow normal cells to recover. 

The total dose of radiation and the number of treatments you need will depend on the size and location of your cancer, type of tumor, your general health, and any other treatments you're receiving.

What happens during each treatment visit?

Before each treatment is given, you may need to change into a hospital gown or robe. It's best to wear clothing that is easy to take off and put on again.

In the treatment room, the radiation therapist will use the marks on your skin to locate the treatment area. You will sit in a special chair or lie down on a treatment table. For each external radiation therapy session, you will be in the treatment room about 15 to 30 minutes, but you will be getting your dose of radiation for only about one to five minutes of that time. Receiving external radiation treatments is painless, just like having an x-ray taken.

The radiation therapist may put special shields (or blocks) between the machine and certain parts of your body to help protect normal tissues and organs. There might also be plastic or plaster forms to help you stay in exactly the right place. 

You will need to remain very still during the treatment so that the radiation reaches only the area where it's needed. The same area is treated each time. You don't have to hold your breath; just breathe normally.

The machine is controlled from a small area that is nearby, so the radiation therapist will leave your treatment room before turning the machine on.  You will be watched on a television screen or through a window in the control room. Although you may feel alone, keep in mind that you can be seen and heard at all times by the therapist, who can talk with you through a speaker.

The machines used for radiation treatments are very large, and they make noises as they move around to aim at the treatment area from different angles. Their size and motion may be frightening at first, so remember that the machines are being moved and controlled by your radiation therapist. They are checked constantly to be sure they're working right.

If you are concerned about anything that happens in the treatment room, ask your therapist to explain.

You will not see or hear the radiation, and most likely, you won't feel anything. If you do feel ill or very uncomfortable during the treatment, tell your therapist at once. The machine can be stopped at any time. 

What are the side effects of radiation treatment?

External radiation therapy does not cause your body to become radioactive. There is no need to avoid being with other people because of your treatment. Even hugging, kissing or having sexual relations poses no radiation exposure risk for others.

Side effects of radiation therapy most often are related to the area that is being treated. Your doctor and nurse will tell you about the possible side effects and how you should deal with them. You should contact your doctor or nurse if you have any unusual symptoms during your treatment, such as coughing, sweating, fever, or unusual pain. Many patients experience no side effects at all from radiation treatment. 

If side effects do occur, it may be helpful to realize that they typically are not serious and can be controlled with medication or diet. They usually go away within a few weeks after treatment ends. However, some side effects can last longer.

Throughout your treatment, your radiation oncologist will regularly check on the effects of the treatment. You may not be aware of changes in the cancer, but if you had symptoms such as pain, bleeding or other discomfort before beginning treatment, you probably will notice decreases, especially after your treatment is completed. You may continue to notice more improvements with time. 

Your doctor probably will recommend some tests to be sure that the radiation is causing as little damage to normal cells as possible. You may have routine blood tests to check the levels of white blood cells and platelets, which may be lower than normal during treatment.

What can I do to take care of myself during therapy?

Each patient's body responds to radiation therapy in its own way. That's why the doctor must plan, and sometimes adjust, your treatment just for you.

Nearly all cancer patients receiving radiation therapy need to take special care of themselves to protect their health and help the treatment succeed. Your doctor or nurse will give you advice on caring for yourself at home that is specific for your treatment. Some general guidelines to remember are given below:

  • Be sure to get plenty of rest. Your body will use a lot of extra energy over the course of your treatment, and you may feel very tired. In fact, fatigue may last for four to six weeks after your treatment is finished. Sleep as often as you feel the need.
  • Good nutrition is a must. Try to eat a balanced diet that will prevent weight loss.
  • Avoid wearing tight clothes, such as shapewear or close-fitting collars over the treatment area. It's best to wear older garments that feel comfortable and that you can wash or throw away if the ink marks rub off on them.
  • Do not use any of these personal-care products in the treatment area without checking first with your doctor: soaps, lotions, deodorants, medicines, perfumes, cosmetics or talcum powder.
  • Do not starch your clothes.
  • Do not rub or scrub treated skin.
  • Do not use adhesive tape on treated skin. If bandaging is necessary, use paper tape. Try to apply the tape outside of the treatment area.
  • Do not apply heat or cold (heating pad, ice pack, etc.) to the treatment area. Even hot water can hurt your skin, so use only lukewarm water for bathing the treated area.
  • Use an electric shaver if you must shave the area, but only after checking with your doctor or nurse.
  • Do not use a pre-shave lotion or hair remover products.
  • Protect the area from the sun. If possible, cover treated skin (with light clothing) before going outside. Ask your doctor if you should use a lotion that contains a sunblock. If so, use a  sunscreen with a sun protection factor (SPF) of at least 15. Reapply the sunscreen often, even after your skin has healed following your treatment. Continue to protect your skin from sunlight after radiation therapy.
  • Be sure your doctor knows about any medicines you are taking before starting treatment. If you need to start taking any new medicines, even aspirin, let your doctor know before you start.

Ask your doctor, nurse, or radiation therapist any questions you have. They are the best experts for advice about your treatment, side effects, at-home care, and any other medical concerns you may have.

How will I know if radiation therapy is working?

After you have started the treatments, your doctor will follow your progress, checking your response to treatment and your overall well-being at least once a week. The treatment plan may be revised by your doctor, if needed.

It's very important that you have all of your scheduled treatments to get the most benefit from your therapy. Unnecessary delays can lessen the effectiveness of your radiation treatment.