Radiation Therapy

Radiation Therapy

Also called: X Ray Therapy, Irradiation, External Radiation, Radiotherapy, External Beam Radiation

Reviewed By:
Martin E. Liebling, M.D., FACP
Mark Oren, M.D., FACP


Radiation therapy uses specific types of radiation to kill or shrink cancer cells. Radiation targets cancer cells and disrupts or destroys their genetic material, preventing the cells from continuing to grow and spread throughout the body.

There are several different types of radiation and methods of delivery, but they can be grouped in two categories:

  • External  beam radiation. The most widely used method of targeting cancer cells with radiation, it uses precise radiation beams from a machine located outside the body. These beams are directed at the tumor or targeted site.
  • Internal radiation (brachytherapy). The source of the radiation (e.g., “seeds,” wires) is given intravenously or by injection. Internal radiation methods include:
    • Intracavitary radiotherapy. The radiation is placed inside an organ, such as the uterus.
    • Interstitial radiotherapy. The radiation source is placed directly inside the tumor or tissue.
    • Systemic radiation. Radioactive materials are delivered through the mouth or by injection and travel throughout the body.

Some radiation types penetrate the body deeply, while others can be more precisely controlled to treat a very small or targeted area. Radiation therapy is sometimes used alone to treat cancer. In other instances, it is combined with other cancer treatments, such as chemotherapy or surgery. Radiation may be used before or after surgery, depending on the type of cancer and the patient’s treatment plan.

While radiation therapy often is effective at treating and controlling cancer, it can damage normal cells that – like cancer cells – grow and divide rapidly. While this damage usually is temporary, it can cause serious side effects for some patients. The potential side effects vary with the type and amount of radiation received and the area being treated.

A patient’s radiation therapy plan will depend on the goal of the treatment, such as shrinking a tumor or destroying any remaining cancer cells. The patient’s general health, tolerance for radiation and goals are considered when balancing the risks of radiation therapy with the potential benefits.

About radiation therapy

Radiation therapy uses external beam x-raysand particles, low penetration electron beams and radioactive isotopes to target and kill cancer cells. Radiation occurs as one of two types – ionizing or nonionizing. Examples of nonionizing radiation include visible light (color), microwaves and radio waves. They are weaker forms of radiation that do not affect the structure of atoms.

Ionizing waves include those used in radiation therapy. They are strong enough to change the structure of atomic particles, which can alter the genetic code of a cell. This prevents the cell from growing and dividing. Radiation is most effective in targeting cells that divide quickly, such as cancer cells. Cells are particularly vulnerable to damage when they are dividing.

However, radiation can damage normal cells that are also characterized by quick division. When damage to normal cells occurs, it causes side effects that are usually temporary, but can be significant. For this reason, physicians try to use a plan that will destroy cancer cells while minimizing damage to surrounding healthy cells.

To help modify a cell’s response to radiation, some cancer patients may be given radioprotectors. Also known as radioprotectants, these chemicals help protect and repair healthy cells that are exposed to radiation therapy.

Currently, there is only one drug approved by the U.S. Food and Drug Administration (FDA) for use as a radioprotector. Known as amifostine (Ethyol), the drug helps reduce the dry mouth that can occur when parotid glands (glands that help to produce saliva) receive a large dose of radiation. This may occur during treatment for salivary gland cancer or head and neck cancers. Researchers are studying the drug to determine if it can be used effectively as a radioprotector to treat other types of cancer. Additional studies are testing other chemicals for use as radioprotectors.   

There are two major types of ionizing radiation: photons and particulate radiation. Photons include x-rays and gamma rays.  Particulate radiation includes:

  • Electrons
  • Protons
  • Neutrons
  • Alpha particles
  • Beta particles

Radiation therapy is used to treat virtually every kind of solid tumor cancer. These include cancers of the:

  • Brain
  • Breast
  • Female reproductive organs (cervix, uterus)
  • Head and neck
  • Internal organs and tissues (lung, pancreas, stomach)
  • Prostate
  • Skin
  • Bone

Leukemia and lymphoma also may be treated with radiation therapy.

In some cases, radiation is used in the early stages of cancer to cure or control the disease. Radiation may be used to shrink tumors prior to surgical removal of the tumor and after surgery to kill any remaining malignant cells. In some situations, radiation is used to lessen the pain of cancer patients and improve their quality of life.

Factors that are used by physicians to determine the appropriate dosage level and duration include:

  • Cancer type and stage
  • Tumor size and sensitivity to radiation
  • Treatment goal
  • Nearby tissues and organs that are vulnerable to radiation damage
  • General health of patient and tolerance for treatment

In addition to treating active cancer cells, radiation can be performed for other reasons:

  • Prophylactic radiation therapy. Radiation is applied to areas that have no evidence of cancer as a means of preventing future cancer in the area.

  • Palliative radiation therapy. Given to reduce pain and other symptoms resulting from cancer that has spread to the bones or other parts of the body.

Types and differences of radiation therapy

Radiation can be delivered by two different methods: external beam radiation therapy and internal radiation therapy (brachytherapy). In the former, the radiation is delivered from a machine outside the body, while the latter involves inserting the source of radiation directly into the body.

Some patients have a combination of radiation therapies that take place either consecutively or concurrently. Several factors will determine the type of radiation delivery to be used, including:

  • Cancer type, stage and location
  • How far the radiation needs to penetrate
  • Known effectiveness of radiation for the cancer type
  • Patient’s general health and medical history
  • Other types of cancer treatments for the patient

External beam radiation therapy

This type of radiation is a non-invasive, non-surgical treatment that delivers high energy x-rays or lower energy electrons. It is performed on an outpatient basis, usually five days a week for five to seven weeks. Delivery of external beam radiation is essentially painless and can be delivered in relatively short sessions. It can be used to treat most types of cancers including cancer of the:

  • Bladder
  • Brain
  • Breast
  • Cervix
  • Head and neck
  • Lung
  • Prostate
  • Vagina

External beam radiation therapy is used primarily to destroy cancer cells in a specific area. It also may be used to relieve pain or other problems associated with cancer that has spread from the primary site to other parts of the body.

External beam radiation therapy varies according to the photon energy produced by the machines, the type of beams that are produced (electrons, x-rays or gamma rays), when the treatment is given and the number of beams used in the procedure.

Other uses of external beam radiation therapy include:

  • Intraoperative radiation therapy (IORT). Used to treat localized cancers that cannot be completely removed or those that are at great risk of recurring in nearby tissues. This form of radiation is given in a single, high-intensity dose immediately following surgery to remove a cancer, while the surgical wound is still open. Special shields are used to protect nearby tissues before the radiation is directed at the tumor site. IORT therapy will likely require a hospital stay. It may be used to treat:

    • Thyroid cancer
    • Colorectal cancer
    • Gynecologic cancers
    • Small intestinal cancer
    • Pancreatic cancer
    •   IORT is also being tested in clinical trials on brain tumors and pelvic sarcomas.
  • Prophylactic cranial irradiation (PCI). Radiation directed at the brain when a primary cancer is known to have a high risk of spreading to the brain.

The energy used in external beam radiation therapy comes from any of the following sources:

  • X-rays. A type of photon (packet of energy) that is widely used in medicine for both diagnosis and treatment. Machines called linear accelerators are used to generate x-rays, with lower-energy beams to destroy cancer cells on the body’s surface and higher-energy beams to kill cancer cells deeper in tissues and organs.

  • Gamma rays. Gamma rays are produced when certain isotopes (one of two or more atoms that have the same number of protons but different numbers of neutrons in their nuclei) break down and release radiation energy. Individual elements break down at different rates and give off varying amounts of energy. The amount of energy determines how deeply the radiation penetrates the body.

  • Particle beams. Particle beams consist of fast-moving subatomic particles and are created by linear accelerators, synchrotrons and cyclotrons that produce and accelerate particles. In particle beam therapy, the beam is produced by a variety of methods. Some particle beams penetrate less deeply into tissue than x-rays and gamma rays. As a result, they are often used to treat cancers on the skin surface or just below the skin.

    Proton beam therapy is a type of particle beam radiation in which protons are deposited over a small area known as the Bragg peak. This allows physicians to deliver high-dose treatments to the tumor while minimizing damage to the healthy tissue in front of and behind the tumor. This form of therapy is not commonly available in the United States and is reserved for cancers that are difficult or dangerous to treat with surgery. In some cases, it is combined with other forms of radiation.

Internal radiation therapy (brachytherapy)

The radiation in this form of therapy is inserted directly into or next to the tumor. The source of the radiation can be injected (housed in special applicators) or implanted. These radiation implants are very small and produce little discomfort. They include:

  • Thin wires
  • Catheters
  • Ribbons
  • Capsules
  • Seeds

Brachytherapy has the advantage of allowing a high dose of radiation to be delivered to a small area. This can be especially useful if the tumor requires high doses of radiation that would be likely to damage normal tissues if a more widespread treatment method, such as external radiation, was used. The source of radiation implanted in brachytherapy can be either permanent or temporary. Permanent pellets eventually use up all the radioactive material and are harmless when left in the body.

Brachytherapy is delivered in the following ways:

  • Interstitial radiation therapy. Inserted into tissue at or near the tumor site, it is sometimes used as an additional dose of radiation after women have received external radiation to treat breast cancer. It also is used to treat cancers of the:

    • Head and neck
    • Prostate
    • Cervix
    • Ovary
    • Perianal and pelvic regions

  • Intracavitary (intraluminal) radiation therapy. Inserted into the body with an applicator to treat uterine cancer. Researchers are also testing the effectiveness of using intracavitary radiation therapy to treat cancers of the:

    • Breast
    • Trachea and bronchia
    • Esophagus
    • Gallbladder
    • Head and neck
    • Cervix and vagina
    • Rectum

  • Systemic radiation therapy. Radioactive materials such as iodine 131 or strontium 89 are injected or given by mouth and will concentrate in certain tissues. Systemic radiation therapy is used to treat cancer of the thyroid and adult non-Hodgkin’s lymphoma.

Patients who receive brachytherapy may be treated as outpatients or may be required to stay in the hospital for a period of time.

Before, during and after radiation therapy

After a physician has determined that radiation therapy is appropriate, the patient will be referred to a radiation oncologist for a series of planning sessions. The oncologist will receive vital information about the patient’s condition, including the results from any scans, pathology reports, surgeries or procedures. The oncologist will consult with other professionals involved in the treatment who are a part of the patient’s cancer care team. Radiation therapy is usually performed at a hospital or medical facility, often one that specializes in cancer treatment.

After reviewing the information, the radiation oncologist will decide which method of radiation will be best. The choice to use external radiation therapy will lead to a process called simulation (sometimes called a marking session). During this process, the physician will use a special x-ray machine that resembles the machine that is used in the actual therapy. With the help of a specialized radiation technician, the physician will:

  • Check tumor size (if present)
  • Identify areas where the cancer may have spread
  • Identify normal tissues in the treatment area
  • Take measurements
  • Mark the area to be radiated

After simulation, the physician will determine the amount of radiation to be delivered. A clinical physicist gives advice on technical matters regarding the radiation therapy, and a dosimetrist helps design the treatment plan customized to the patient’s needs.

Radiation dosage is measured by the amount of radiation absorbed by the tissues. Scientists use a unit known as a gray (Gy) to calculate this measurement and different tissues can tolerate different amounts of radiation measured in centigrays (cGy). For example, the liver can tolerate 3,000 cGy, the lungs 2,000 cGy and the kidneys 1,800 cGy.

The physician will use a therapeutic ratio to calculate the most effective dosage level. The therapeutic ratio compares the damage inflicted on cancer cells with the damage likely to occur to normal cells. Once a total dosage amount has been selected, it is divided into smaller amounts that are administered over individual treatment sessions. This is called the fractionation schedule, and it allows the physician to maximize the treatment’s ability to kill cancer cells while minimizing any incidental damage to normal cells by giving the body rest periods to recover.

Prior to beginning treatment, patients also may receive long-lasting, but tiny tattoo marks at the spot where the radiation is to be delivered. This will ensure that the radiation is directed precisely at the appropriate target during each treatment session. The tattoos provide important placement information should any future radiation be necessary. Prior to treatment, the physician may create a mold or device to help keep the patient in the proper place during the sessions. It also helps ensure that only the targeted area is treated.

During an external beam radiation treatment session, the patient is placed in the proper position using predetermined measurements and molds, if necessary. Radiation shields may be placed to protect areas that are not part of the treatment. As the radiation is delivered, the machine being used for the procedure may be rotated around the patient’s body to deliver radiation from different angles. A treatment session typically lasts for 15 to 20 minutes, although the actual radiation exposure time is much less.

External radiation treatments typically are scheduled on a daily basis, five days a week over a period of five to seven weeks. In some cases, patients will be treated twice daily.

Patients who receive internal radiation therapywill likely have the radiation source placement performed in a single session. If the placement is temporary, it will be removed anywhere from several minutes to a few days after it has been inserted.

The dosage and schedule for temporary brachytherapy varies depending on several factors, including the type and location of the cancer. In high-dose rate (HDR) brachytherapy, the patient may receive short, intense sessions that are repeated several times a day. HDR brachytherapy may continue for one to two weeks before the implant device is removed.

Low-dose rate (LDR) brachytherapy provides a continuous dose of radiation over several hours or days. These patients may be required to remain in the hospital during the treatment period until the device is removed.

Radiation therapy is usually performed on an outpatient basis, with most patients returning home after the procedure. However, some patients may be required to remain in the hospital for a short stay. Patients who have internal radiation therapy may be restricted from some degree of exposure to others for a short period of time. This is to prevent others from coming into contact with radiation that may escape from the body.

Potential risks with radiation therapy

Some forms of radiation therapy may make patients radioactive for a certain period of time. External radiation therapy does not pose this risk, but internal radiation therapy does create an area of radioactivity around the implant. In addition, systemic radiation therapy involves radioactive materials circulating throughout the body. In these cases, some of this material leaves the body through saliva, sweat and urine. Certain precautions may be necessary to protect medical staff, visitors and others who come into contact with the patient following systemic radiation and internal radiation therapy.

Patients may be advised to observe the following:

  • Wash hands thoroughly after using the toilet
  • Flush the toilet several times after each use
  • Use eating utensils and towels that are kept separate from others
  • Do laundry separately
  • Drink plenty of fluids to flush radioactive iodine from the body
  • Avoid kissing and sexual contact
  • Avoid prolonged contact with infants, children and pregnant women

While radiation therapy can be highly beneficial to cancer patients, it also can cause significant side effects. These are the result of damage to normal cells incurred during treatment. They usually will disappear once treatment has ended. Some side effects are general while others are likely to occur in the area being treated. Side effects can include:

  • Fatigue. This is a symptom generally associated with radiation, but its cause is unknown. There is no single treatment for fatigue, but physicians can sometimes offer relief by treating the underlying causes of symptoms. Patients may be instructed to take more frequent naps or modify their daily activities. Also if a patient has anemia, blood transfusions or medications may be ordered to stimulate production of red blood cells.
  • Skin problems. Early in treatment, a faint redness may develop at the site, followed by dryness and peeling. The skin may also become darker and itchy. Moisturizers may help relieve these symptoms. In some patients, extreme weeping and peeling may eventually develop, or thinning or hardening of the skin. A physician can best address how to treat these developments.
  • Mouth problems. Inflammation of the mouth lining (mucositis) may occur with radiation in the head and neck area. Dryness and loss of taste in the mouth also can occur, and can be permanent in the worst cases. Some patients may develope dysphagia (swallowing problems) during the treatment period. These individuals may be referred to a speech-language pathologist for therapy or to a dietitian for nutritional support.

    Head and neck cancer patients may be given a radioprotector to help protect healthy tissues from radiation damage. Medications also can be prescribed to improve saliva production. Patients should be careful to keep their mouths clean to reduce the chance of infection. Finally, radiation can sometimes increase the chance of dental problems, such as cavities or loss of teeth. A dentist should be consulted about preventative care prior to radiation treatments of the head and neck.
  • Cognitive problems. Significant changes in brain function can sometimes occur when the radiation is for primary or metastatic brain cancers. These problems can include memory loss, diminished sexual desire and poor tolerance of cold temperatures. In some cases, a large area of dead cells collects in the brain, a condition known as radiation necrosis. This occurs months to years after radiation treatments. In rare cases it can be fatal.   
  • Lung problems. Radiation treatments of the chest area can cause a decrease in surfactant, the substance that keeps the air passages open. This may result in coughing and shortness of breath. Steroids are sometimes prescribed to reduce inflammation. Fibrosis (stiffening and scarring) can occur later, significantly reducing breathing capacity.
  • Cardiac problems. Radiation therapy to the chest has been associated with eventual development of heart disease, including heart attacks. Such problems have occurred many years after radiation treatment and in many cases, the treatment involved much stronger doses of radiation than are currently used for most cancers.
  • Gastrointestinal tract. Radiation in the abdomen may result in swelling or inflammation of the esophagus or intestines. This can cause nausea, vomiting or diarrhea. Antacids can help, as can a diet low in spicy, fried or high-fiber foods. For patients who develop severe nausea and vomiting, certain prescription drugs may help reduce these side effects. In severe cases, dehydration may require administration of intravenous fluids.
  • Reproductive organs. Radiation of the testicles can cause permanent loss of sperm production, while radiation of the abdomen in women can damage the ovaries. In most cases, only one ovary will be involved in radiation therapy, which lessens the likelihood of infertility.

    Pelvic radiation can cause the vagina to become tender and inflamed for weeks following radiation. Scarring can narrow the vagina, making intercourse difficult. Pelvic radiation can also damage the arteries that carry blood to the penis, making it difficult to maintain erections.
  • Secondary cancers. Radiation therapy now targets cancers mores precisely, which makes the development of second cancers less of a problem than in the past. The risk remains, but it is low and should be weighed against the potentially life-saving benefits of radiation therapy.

Ongoing research regarding radiation therapy

Currently, researchers are working on a number of refinements to external radiation therapy. These include:

  • Three-dimensional (3-D) conformal radiation therapy. This builds on the traditional two-dimensional planning of radiation treatments, which has involved just width and height. Computer technology creates three-dimensional images that also add depth. This allows physicians to more precisely target tumors with beams of radiation that actually conform to the shape of the tumor. The 3-D image of the tumor can be generated using computed axial tomography (CAT), magnetic resonance imaging (MRI), positron emission tomography (PET) or single photon emission computed tomography (SPECT). 
  • Intensity-modulated radiation therapy (IMRT). A new type of three-dimensional conformal radiation therapy that uses radiation beams of varying intensities to deliver different doses of radiation to small areas of tissue at the same time. This results in even greater precision, allowing the physician to deliver higher doses of radiation inside the tumor and lower doses to nearby healthy tissue. A linear accelerator delivers the radiation, and the equipment can be rotated around the patient to ensure that radiation beams are sent from optimal angles. The technology has been used to treat cancers of the brain, head and neck, nasopharynx, breast, liver, lung, prostate, and uterus. Additional research is being conducted on using a combination of this technology with mixed beam radiation therapy (MBRT) to deliver more precise beams to the targeted sites.
  • Stereotatic radiation therapy. Delivers a large dose of radiation precisely to a small tumor area. This is most often used in cancers of the brain, but is also being tried on other types of cancer. Linear accelerators or other machines called gamma knives are used to deliver this treatment. The treatments do not remove the tumors but disrupt the DNA of the tumor cells. The cells are no longer able to reproduce and as a result, the tumors shrink over a period of time. These non-surgical procedures are being used in various medical centers to treat many types of brain tumors.
  • Proton beam radiation therapy.Protons are positively-charged atoms that can be used in beams to radiate tumors. The proton beam may be better for destroying cancer cells while causing less damage to nearby healthy tissues. This type of radiation requires expensive equipment and a specialized staff. For those reasons, there are very few treatment centers in the United States that offer proton beam therapy. In addition, more studies are needed to determine which cancers are best suited for this type of radiation as well as its long-term effectiveness.
  • Intraoperative radiation therapy (IORT). This therapy involves the use of radiation to treat the cancer during surgery. It may be combined with external or internal radiation that is given before or after surgery. Researchers have found IORT to be beneficial to cancers of the abdomen or pelvic region. During IORT, physicians are able to protect nearby normal tissues by moving them out of the targeted radiation beam. IORT is performed in a specialized operating room – one that has been fitted with radiation shields on the surrounding walls.

There are other new approaches to radiation therapy that are being tested. Among the most promising is hyperthermia, which is the use of heat. It is being studied in conjunction with radiation therapy and the combination of treatments appears to increase the effectiveness of radiation on certain tumors.

The use of radiolabeled antibodies also appears to be another promising avenue for radiation treatments. Antibodies are proteins made by the body in response to antigens, which are substances that the immune system recognizes as foreign. Some cancer cells have specific antigens that trigger the production of antibodies specific to tumors. Researchers are developing antibodies and attaching them to radioactive substances that are then injected into the body. Once inside the body, the antibodies seek out the cancer cells, which are then destroyed by the attached radiation. Scientists are also working to develop new radiosensitizers and radioprotectors to increase the effectiveness of radiation and chemotherapy while protecting normal tissues. Some of these drugs are being used in clinical trials for various cancers.

Research is also being conducted on the optimal scheduling and dosages for cancers. For examle, a recent study has found that using intensity-modulated radiation therpay for breast cancer patients may reduce radiation treatment time from six to seven weeks to four weeks.

Studies continue to examine the effectiveness of radiation therapy in conjunction with other treatments, such as biological therapy and surgery. In addition, researchers continue to evaluate the success of radiation therapy in preventing recurrence of cancers and extending survival.

Questions for your doctor on radiation therapy

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor or healthcare professional the following questions about radiation therapy:

  1. Is radiation therapy necessary for my type and stage of cancer?
  2. What type of radiation therapy will I receive?
  3. If I receive internal radiation therapy, will the radiation implants be permanent or temporary?
  4. Where will I go for radiation therapy and who will administer it?
  5. When will I begin radiation and what will be my schedule?
  6. How long does each session last?
  7. What side effects can I expect?
  8. What can I do to lessen the side effects?
  9. Will these side effects stop after I finish radiation therapy?
  10. Are there precautions I should take while receiving radiation therapy?
  11. How will you determine if the radiation treatments are successful?
  12. What are the chances that my cancer will recur?
  13. If the radiation therapy does not work, will it be repeated?
  14. Will I need other cancer treatments?
  15. How will radiation affect the timing of these treatments?
  16. Are the markings on my skin permanent?
  17. Will radiation treatment increase my risk for other cancers?
  18. How will radiation treatments affect my fertility?
  19. Can I do anything to prevent damage to my reproductive organs?
  20. Am I a candidate for any clinical trials?
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