Radiation therapy: Using radioactivity to kill cancer cells

You may have heard that radiation is hazardous to your health. But when it comes to cancer treatment, the use of carefully targeted and regulated doses of high-energy radiation — radiation therapy — can be lifesaving.

More than half of all people with cancer receive some type of radiation therapy to kill cancer cells. Radiation therapy may be your only cancer treatment, or it may be used in conjunction with other cancer treatments, such as surgery and chemotherapy. If your doctor recommends radiation therapy to treat your cancer, you may have concerns about what it means for you.

How radiation therapy works

Radiation therapy — also called radiotherapy or X-ray therapy — involves treating cancer with beams of high-energy particles, or waves (radiation), such as gamma rays or X-rays. You may be familiar with the use of radiation in the form of diagnostic chest X-rays, computerized tomography (CT) scans or dental X-rays. But radiation therapy relies on much higher X-ray energy delivered at many more times that dose in order to treat cancer.

Radiation therapy damages cells by destroying the genetic material that controls how cells grow and divide. And while both healthy and cancerous cells are damaged by radiation, the goal of treatment is to hurt as few normal, healthy cells as possible.

You may be worried about radiation destroying healthy cells as well as the cancerous cells. But radiation is much more harmful to cancer cells than it is to normal cells. This is because cancer cells divide more rapidly than do healthy cells. Cells are more vulnerable to damage when they're dividing, making cancer cells more susceptible to radiation than normal cells are. In addition, normal cells can recover from the effects of radiation more easily than cancer cells can.

How radiation therapy is used in your cancer treatment

Your doctor may suggest radiation therapy as an option at different times during your cancer treatment and for different reasons, including:

• Before surgery, to shrink a cancerous tumor (neoadjuvant therapy)
• During surgery, to direct large doses of radiation directly at a tumor
• After surgery, to stop the growth of any remaining cancer cells (adjuvant therapy)
• In combination with other treatments, such as chemotherapy, to destroy cancer cells

In addition, radiation therapy is sometimes used to shrink tumors to decrease the pressure, pain or other symptoms they may cause. This type of treatment is sometimes called palliative care.

Types of radiation therapy

Radiation is useful in treating many types of cancers in many parts of the body. Radiation therapy can be delivered in two ways: externally or internally.

External radiation
In external radiation, treatment comes from a machine outside your body. External beam radiation is the most common radiation treatment method used. This radiation comes from a machine such as a linear accelerator. It allows your doctor to treat large areas of your body and multiple areas if your cancer has spread.

External beam radiation is most often used on a specific area of your body, for instance a tumor. In some cases it may be used over your whole body. For example, whole-body radiation is sometimes used before a bone marrow transplant to ready your body to accept the new bone marrow cells.

You typically receive external beam radiation on an outpatient basis about five days a week over a period of one to eight weeks. In some cases, a single treatment may be used to help relieve pain or other symptoms associated with more advanced cancers. During a treatment session, you'll be asked to lie down. You might be positioned with molds to hold you in place and with shields to block radiation from reaching certain parts of your body. The machine may rotate around your body to reach the target from different directions. Treatment sessions last approximately 15 to 30 minutes.

External beam radiation uses a variety of energy sources, including photons, such as X-rays and gamma rays, and particle beams, such as electrons, protons and neutrons. Each differs in the type of energy emitted, the amount of area it can cover and how deeply it can penetrate your body. Depending on your type of cancer, your radiation oncologist — a doctor who specializes in treating cancer with radiation — will choose the type of energy best suited for your treatment.

Beyond external beam radiation, other types of external radiation include:

• Intraoperative radiation therapy (IORT). If your cancer can't be completely removed with surgery, you might receive IORT during surgery. Your surgeon removes as much of the cancer as he or she can, then your radiation oncologist aims a large dose of high-energy radiation at the remaining tumor. IORT is also used in cancers that are localized but have a high risk of recurring.
• Three-dimensional conformal radiation therapy. This type of radiation uses imaging machines, such as the CT scan, to make a three-dimensional map of your cancer. The radiation beams are directed to take the shape of your cancer — to conform to its shape. Conformal radiation better protects the healthy tissue around your cancer than do traditional radiation techniques.
• Intensity-modulated radiation therapy (IMRT). IMRT is a type of conformal radiation. Based on the three-dimensional map of your cancer, IMRT varies the intensity of the radiation beams. For instance, stronger beams can be focused at larger areas of your tumor and weaker beams can be directed to smaller areas closer to healthy tissue.
• Stereotactic radiosurgery. Radiosurgery doesn't actually involve surgery. Instead it focuses high-powered radiation in one large dose to a brain tumor that can't be removed through standard surgery. One type of stereotactic radiosurgery is called gamma-knife radiosurgery.
• Radiation combined with extreme heat (hyperthermia). Microwaves and ultrasound create heat that can kill cancer cells. But using hyperthermia in combination with radiation is proving to be more effective.

Internal radiation
Also known as brachytherapy (brak-e-THER-uh-pee), internal radiation is typically used when your doctor needs to deliver a high dose of radiation to a small area. Rather than coming from machines outside your body, the radiation source is placed inside your body. Most often, the radioactive material — encased in wires, seeds, capsules or tubes (catheters) — is placed inside your tumor or very close to it.

Internal radiation implants containing radioactive material are usually placed during surgery or using a needle. Brachytherapy may include placing implants inside a body cavity, such as the vagina (a technique called intracavitary radiation) or by putting radioactive material directly into body tissue (called interstitial radiation). In both instances placement is usually done once, though it may be done up to several times, and is temporary, lasting from a few minutes to several days. In some cases, such as prostate cancer, interstitial radiation may be permanent, though the radioactivity of the radioactive material diminishes over time.

Internal radiation can also be given systemically, meaning it travels throughout your body. Also called radiopharmaceutical therapy or liquid radiation, systemic radiation uses radioactive material mixed in a solution. This type of radiation can be given intravenously through an IV, by mouth or it can be injected into a body cavity. For instance, if cancer has spread to your bones, it might be inefficient to aim external radiation at every small spot where cancer has spread. But by giving radiation through an IV, the radioactive material can travel through the blood to each cancer site.

Your doctor may restrict how frequently and closely you have contact with people while you're receiving internal radiation. This is because some treatments allow radiation to escape, and it's important to limit unnecessary radiation exposure to others.

Side effects of radiation therapy

Side effects of radiation therapy greatly depend on which part of your body is being radiated and how much radiation is used. You may experience no side effects, or you may experience several. Most side effects are temporary, can be controlled and generally disappear over time once treatment has ended.

Some side effects may develop later. For example, in rare circumstances a new cancer (second primary cancer) that's different from the first one treated with radiation may develop years later. Or, in cases in which radiation is given to the chest area, late effects may include scarring of the lungs (pulmonary fibrosis), which can make breathing more difficult. Ask your doctor about potential side effects, both short and long term, immediate and delayed, that may arise after your treatment.

Radiation research: Evolving therapies

Researchers continue to develop new methods for delivering radiation therapy, always with the goal of directing a high dose of radiation to the tumor while protecting surrounding tissue. Examples of other methods being studied include:

• Drugs that protect healthy cells (radioprotectors). These drugs are designed to protect normal cells from radiation. One example is the intravenous drug amifostine (Ethyol), an antioxidant. Though it's being used successfully to protect salivary glands from damage during radiation to the head and neck, more studies are being conducted to see whether it and other drugs might protect healthy tissue in other areas of the body that receive radiation treatment.
• Drugs that make cancer more sensitive to treatment (radiosensitizers). These drugs modify the cancerous cells to make them more susceptible to the radiation. Several drugs are being studied as sensitizers. Some chemotherapy drugs, including fluorouracil (Adrucil) and cisplatin (Platinol), work as radiation sensitizers.
• Treatment delivered directly to cancer cells (radioimmunotherapy). This treatment targets radiation directly to the cancer. Radioactive substances are attached to special proteins called antibodies. These antibodies are attracted to the cancer cells by signals cancer cells give off. When the antibodies reach the cancer cells, they release the radiation, killing the cancer cells. Radioimmunotherapy is being studied in many types of cancers. Two radioimmunotherapy drugs — ibritumomab tiuxetan (Zevalin) and tositumomab (Bexxar) — have already been approved for use in advanced non-Hodgkin's lymphoma.

Innovations in radiation may be available to you in clinical trials. Talk with your doctor about whether you might qualify for a trial.

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Slide show: Radiation therapy treatment planning