Radiation therapy for breast cancer uses high-energy X-rays, protons or other particles to kill cancer cells. Rapidly growing cells, such as cancer cells, are more susceptible to the effects of radiation therapy than are normal cells.

The X-rays or particles are painless and invisible. You are not radioactive after treatment, so it is safe to be around other people, including children.

Radiation therapy for breast cancer may be delivered in two ways:

  • External radiation. A machine delivers radiation from outside your body to the breast. This is the most common type of radiation therapy used for breast cancer.
  • Internal radiation (brachytherapy). After you have surgery to remove the tumor, your doctor temporarily places a radiation-delivery device in your breast near the tumor site. He or she then places a radioactive source into the device for short periods of time over the course of your treatment.

Radiation therapy may be used to treat breast cancer at almost every stage. Radiation therapy is an effective way to reduce your risk of breast cancer recurring after surgery. In addition, it is commonly used to ease the symptoms caused by cancer that has spread to other parts of the body (metastatic breast cancer).

Mayo Clinic's approach

Why it's done

Radiation therapy kills cancer cells. It is used after surgery to help prevent recurrence. It can also be used to provide relief from pain and other symptoms of advanced breast cancer.

Here are the main ways radiation therapy is used to treat breast cancer. Discuss these treatment options with a doctor who specializes in radiation therapy for cancer (radiation oncologist).

Radiation after lumpectomy

After a lumpectomy for breast cancer, radiation therapy is typically used. Lumpectomy is a surgery that removes only the tumor and a small amount of normal breast tissue around it. Adding radiation after a lumpectomy lowers the risk of cancer recurrence in the affected breast. Recurrences can take place months or years later because of cancer cells left behind after surgery. Radiation helps to destroy remaining cancer cells.

Lumpectomy combined with radiation therapy is often referred to as breast conservation therapy. In clinical trials comparing lumpectomy with and without radiation therapy, the addition of radiation therapy resulted in significantly decreased rates of breast cancer recurrence and proved to be as effective as having the entire breast removed. In special situations if the risk of recurrence is very low, your radiation oncologist may also discuss the option of avoiding radiation after a lumpectomy.

  • External beam radiation of the whole breast. One of the most common types of radiation therapy after a lumpectomy is external beam radiation of the whole breast (whole-breast irradiation). The entire schedule of radiation therapy (course) is divided into daily treatments (fractions).

    For many years, whole-breast irradiation was typically delivered in one radiation treatment a day, five days a week (usually Monday through Friday), for about five to six weeks. Accelerated radiation approaches are now common. For example, with an approach called hypofractionated radiation therapy, you receive slightly larger doses in fewer sessions. This shortens the entire regimen by two weeks, enabling the treatment to be completed in three to four weeks. Clinical trials have shown that these shorter regimens work as well as longer regimens at preventing recurrences of breast cancer and may reduce the risk of some side effects.

  • Partial-breast irradiation. For some women with early-stage breast cancer, partial-breast radiation may be an option. The radiation therapy is directed to the area around where the tumor was removed, which is at highest risk of having any remaining cancer cells. This radiation can be delivered internally with brachytherapy or externally with X-rays (photons) or protons. Because a smaller area is treated, treatment schedules may be shorter, such as one to two treatments a day over three to five days.

Radiation after mastectomy

Removal of the entire breast (mastectomy) does not eliminate the risk of recurrence in the remaining tissues of the chest wall or lymph nodes. In many situations, the risk of recurrence is high enough that radiation is recommended after mastectomy. This type of radiation is called post-mastectomy radiation therapy and is typically administered five days a week for five to six weeks.

Factors that may put you at a high enough risk of breast cancer recurrence in your chest wall or lymph nodes to warrant consideration of radiation after mastectomy include:

  • Lymph nodes with signs of breast cancer. Underarm (axillary) lymph nodes that test positive for cancer cells are an indication that some cancer cells have spread from the primary tumor.
  • Large tumor size. A tumor greater than about 2 inches (5 centimeters) generally carries a higher risk of recurrence than do smaller tumors.
  • Tissue margins with signs of breast cancer. After breast tissue is removed, the margins of the tissue are examined for signs of cancer cells. Very narrow margins or margins that test positive for cancer cells are a risk factor for recurrence.

Radiation for locally advanced breast cancer

Radiation therapy can also be used to treat:

  • Breast tumors that cannot be surgically removed.
  • Inflammatory breast cancer, an aggressive type of cancer that spreads to the lymph channels of the skin covering the breast. People who have this type of cancer typically receive chemotherapy before a mastectomy, followed by radiation, to decrease the chance of recurrence.

Radiation for managing metastatic breast cancer

If breast cancer has spread to other parts of your body (metastasized) and a tumor is causing pain or some other symptom, radiation can be used to shrink the tumor and ease that symptom.

Proton therapy

Proton therapy offers more precise radiation dose delivery to the treatment target and protection of nearby healthy tissue. This is because proton beams, unlike X-rays, do not travel beyond the target. Therefore, researchers hope that proton therapy will decrease the risk of serious long-term complications of radiation therapy. However, proton therapy still carries risk of side effects because the targeted area may contain skin, muscle, nerves and other important tissue.

Proton therapy is being researched in patients with early-stage and locally advanced breast cancer.


Side effects from radiation therapy differ significantly depending on the type of treatment and which tissues are treated. Side effects tend to be most pronounced toward the end of your radiation treatment. After your sessions are complete, it may be several days or weeks before side effects clear up.

Common side effects during treatment may include:

  • Mild to moderate fatigue
  • Skin irritation — such as itchiness, redness, peeling or blistering — similar to what you might experience with a sunburn
  • Breast swelling
  • Changes in skin sensation

Depending on which tissues are exposed, radiation therapy may cause or increase the risk of:

  • Arm swelling (lymphedema) if the lymph nodes under the arm are treated
  • Damage or complications leading to removal of an implant in women who have a mastectomy and undergo breast reconstruction with an implant
  • Rib fracture or chest wall tenderness, rarely
  • Inflamed lung tissue or heart damage, rarely
  • Secondary cancers, such as bone or muscle cancers (sarcomas) or lung cancer, very rarely

How you prepare

A doctor helps a woman prepare for radiation therapy.

A doctor helps a woman prepare for radiation therapy.

You will meet with your radiation therapy team, health care professionals who work together to plan and provide your radiation treatment. Team members usually include:

  • A radiation oncologist, a doctor who specializes in treating cancer with radiation. Your radiation oncologist determines the appropriate therapy for you, follows your progress and adjusts your treatment, if necessary.
  • A radiation oncology medical physicist and a dosimetrist, who make calculations and measurements regarding your radiation dosage and its delivery.
  • A radiation oncology nurse, nurse practitioner or physician assistant, who answers questions about the treatments and side effects and helps you manage your health during treatment.
  • Radiation therapists, who operate the radiation equipment and administer your treatments.

Before you begin treatment, your radiation oncologist will review your medical history with you and give you a physical exam to assess whether you would benefit from radiation therapy. Your oncologist will also discuss the potential benefits and side effects of your radiation therapy.

External radiation therapy

Before your first treatment session, you'll go through a radiation therapy planning session (simulation), in which a radiation oncologist carefully maps your breast area to target the precise location of your treatment. During the simulation:

  • A radiation therapist helps you into a position best suited to target the affected area and avoid damage to surrounding normal tissue. Sometimes pads or other devices are used to help you hold the position.
  • You have a CT scan so that the radiation oncologist can locate the treatment area and normal tissues to avoid. You'll hear noise from the CT equipment as it moves around you. Try to relax and remain as still as possible to help ensure consistent, accurate treatments.
  • A radiation therapist may mark your body with semipermanent ink, or with tiny permanent tattoo dots. These marks will guide the radiation therapist in administering the radiation. You will be asked to avoid scrubbing away the marks.
  • The dosimetrist, radiation physicist and radiation oncologist use computer software to plan the radiation treatment you will receive. Once the simulation and planning are complete and multiple quality assurance checks are done, you can begin treatment.

Internal radiation therapy

Before internal radiation therapy (brachytherapy) is started, a special device for placement of the radioactive material is placed in the area from where the tumor was taken (tumor bed). This may be done during your cancer surgery or as a separate procedure several days later.

What you can expect

Radiation therapy usually begins three to eight weeks after surgery unless chemotherapy is planned. When chemotherapy is planned, radiation usually starts three to four weeks after chemotherapy is finished. You will likely get radiation therapy as an outpatient at a hospital or other treatment facility.

A common treatment schedule (course) includes one radiation treatment a day, five days a week (usually Monday through Friday), for about five to six weeks. Spreading out your sessions helps your healthy cells recover from radiation exposure while cancer cells die.

Whole-breast irradiation can frequently be shortened to three to four weeks. In addition, partial-breast irradiation may be completed in five days or less. Your radiation oncologist can help decide the course that is right for you.

External radiation

A typical external radiation therapy session generally follows this process:

  • When you arrive at the hospital or treatment facility, you're taken to a special room that's used specifically for radiation therapy.
  • You may need to remove your clothes and put on a hospital gown.
  • The radiation therapist helps you into the position you were in during the simulation process.
  • The therapist may take images or X-rays to ensure you are positioned correctly.
  • The therapist leaves the room and turns on the machine that delivers the radiation (linear accelerator).
  • Although the therapist isn't in the room during the treatment, he or she will monitor you from another room on a television screen. Usually you and the therapist can talk through an intercom. If you feel sick or uncomfortable, tell your therapist, who can stop the process if necessary.

Delivery of the radiation may last only a few minutes, but expect to spend 15 to 45 minutes for each session, as it can take several minutes to set you up in the exact same position each day. This step ensures precise radiation therapy delivery.

Radiation therapy is painless. You may feel some discomfort from lying in the required position, but this is generally short-lived.

After the session, you're free to go about your regular activities. Take any self-care steps at home that your doctor or nurse recommends, such as taking care of your skin.

In some cases, once the main radiation therapy sessions have been completed, your doctor may recommend a radiation boost. This commonly means four to five additional days or fractions of radiation directed at the place of highest concern. For example, after whole-breast irradiation is complete, a boost of radiation is commonly given to area where the tumor was removed from (lumpectomy cavity).

Internal radiation

For internal radiation, the radioactive source is inserted once or twice a day for a few minutes in the implanted radiation delivery device. This is usually done on an outpatient basis, and you can leave between sessions.

After the course of treatment, the radiation delivery device is removed. You may be given pain medication before the radiation delivery device is removed. The area may be sore or tender for several days or weeks as the tissue recovers from the surgery and radiation.


After you complete radiation therapy, your radiation oncologist or other medical providers will schedule follow-up visits to monitor your progress, look for late side effects and check for signs of cancer recurrence. Make a list of questions you want to ask your medical providers.

After your radiation therapy is completed, tell your medical providers if you experience:

  • Persistent pain
  • New lumps, bruises, rashes or swelling
  • Unexplained weight loss
  • A fever or cough that doesn't go away
  • Any other bothersome symptoms

Clinical trials

Explore Mayo Clinic studies of tests and procedures to help prevent, detect, treat or manage conditions.

Radiation therapy for breast cancer care at Mayo Clinic

March 24, 2018
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Radiation therapy for breast cancer