Radiation Therapy for Breast Cancer

April 10, 2025

This page was reviewed under our medical and editorial policy by Susan Yost, Ph.D., staff scientist, Department of Medical Oncology & Therapeutics Research, City of Hope^® Cancer Center Duarte

Radiation therapy is a common treatment for women diagnosed with breast cancer. It is sometimes called radiotherapy or irradiation, and it may be used to treat:

• Early-stage breast cancer (including ductal carcinoma in situ or DCIS, the earliest stage of breast cancer)
• Locally advanced breast cancer
• The symptoms of advanced-stage (metastatic) breast cancer, such as chest, breast or bone pain
• Inflammatory breast cancer (IBC)
• Recurrent breast cancer (breast cancer that returned)

An expert called a radiation oncologist works with each patient, her cancer care doctors and surgical team to help optimize her radiation therapy treatment plan.

What Is Radiation for Breast Cancer?

Radiation is a form of therapy that uses high-energy particles to destroy breast cancer cells and reduce the size of breast tumors.

Radiation therapy treatments are typically pain-free and rely on energy from tiny particles, such as:

• X-rays
• Protons
• Gamma rays
• Neutrons

These high-energy particles work by damaging breast cancer cell DNA, the genetic instructions for cell development, so cells are no longer able to divide and eventually die. These particles tend to harm fast-growing cells like cancer cells more than they do normal cells that grow at a slower rate.

There are two main types of radiation therapy for breast cancer:

• External beam radiation therapy (EBRT), which uses a machine that directs radiation particles from outside the body to the breast tissue or lymph nodes
• Brachytherapy (internal radiation), which uses a device containing radioactive pellets (seeds) placed into breast tissue

For breast cancer, both EBRT and brachytherapy are largely local treatments, meaning they target and treat the region where the breast tumor is present rather than the whole body (systemic radiation therapy) through means such as an intravenous (IV) line. The aim of local treatment is to help reduce radiation damage to nearby cells so they will continue to function normally.

External Beam Radiation Therapy (EBRT)

EBRT is the most common type of radiation therapy used to treat breast cancer. It focuses radiation from a machine onto the breast and includes:

• Whole breast radiation to treat the entire breast, including the chest wall and axillary (armpit) lymph nodes
• Accelerated partial breast irradiation to treat only the tumor bed (cavity where the cancer was removed) with higher-dose radiation delivered over a shorter period of time
• Chest wall radiation to treat the mastectomy (whole breast removal) surgery area and scar
• Lymph node radiation to treat cancer in the lymph nodes under the arm (axillary), above the collarbone (supraclavicular) or behind the center chest breast bone (internal mammary)

For patients undergoing whole breast radiation, radiation mapping for breast cancer is performed. This is sometimes called simulation or sim. During sim, the radiation oncologist may go over the patient’s medical history, perform a physical exam and scans such as magnetic resonance imaging (MRI) to clearly identify and sometimes mark with tattoos (ink or other markers) the precise location of the cancer and normal tissues. This allows for more targeted radiation delivery.

Sometimes whole breast radiation is delivered as hypofractionated radiation therapy. Patients may receive higher doses of radiation five days a week over about three to four weeks, as opposed to the smaller doses delivered five days a week over six to seven weeks with standard whole breast radiation. Benefits to the patient may include fewer side effects and a shorter therapy schedule.

Patients may also receive one of three types of accelerated partial breast irradiation.

Intraoperative radiation therapy (IORT): During breast cancer surgery, one large dose of radiation is delivered to the tumor bed right before the procedure ends.

3D conformal radiotherapy (3D-CRT): Radiation beams are aimed from multiple directions to match the tumor’s shape and help accelerate cancer cell damage while reducing harm to surrounding tissues.

Intensity-modulated radiotherapy (IMRT): This is similar to 3D-CRT, except beam strengths may be altered as they hit different parts of the tumor.

Proton Therapy

Protons are tiny particles with a positive charge. As its name suggests, proton radiation therapy delivers beams of protons to the breast tumor, via special machines called particle accelerators. The beams are administered without being seen or felt by the patient, making it a pain-free experience.

Proton therapy differs from X-ray radiation in that the beam stops at the tumor, rather than extending beyond it. This allows for delivery of more radiation while reducing treatment side effects and the risk of damage to nearby healthy tissues.

Stereotactic Radiation Therapy

Stereotactic radiation therapy or radiosurgery is a type of photon (X-ray or gamma ray) therapy that relies on specialized equipment — such as a machine that delivers highly focused gamma rays — to direct precise radiation to the cancer cells. It is typically used for smaller tumors and given either in one session or in smaller doses over several days, making the length of treatment shorter than with whole breast therapy.

Like proton therapy, stereotactic radiation therapy may limit damage to surrounding tissues. However, due to its focus on a small spot, it is not as appropriate for use on larger tumors or cancer that has spread into lymph nodes.

Intraoperative Radiation Therapy (IORT)

While a patient is still under anesthesia during a breast cancer operation, the care team may opt to give one large dose of photon or particle beam (electron) radiation to the spot where the tumor(s) was before removal. This is known as intraoperative radiation therapy or IORT. It is typically used during a lumpectomy (also known as breast-conserving surgery, or BCS). The surgical team may use a balloon, cone or other technology to deliver the treatment directly to the tumor bed.

IORT may replace traditional whole breast radiation therapy for women with early-stage breast cancer whose cancer has not spread to lymph nodes or beyond the tumor edges. This type of breast radiation therapy offers several advantages, including:

• Optimal views of the cancer edges to reduce the risk of missing treating certain areas
• Greater convenience for women whose schedule makes it difficult to keep up with postsurgical radiation treatments
• Eliminating the risk of missing scheduled radiation treatments when weighing the pros and cons of breast-conserving surgery and mastectomy

One disadvantage of IORT is that the final pathology report about the cancer is not complete at the time of the treatment. This means the cancer may have unknown factors that make postsurgical whole breast radiation therapy necessary.

Brachytherapy or Internal Radiation

Brachytherapy is a type of internal accelerated partial breast irradiation. With this type of radiation therapy, a device containing pellets of radioactive material is placed inside the breast tissue where cancer cells are located. The pellets or seeds irradiate the cells over a short period.

The procedure is done after lumpectomy for smaller tumors less than an inch in size. There are two types of brachytherapy.

Intracavitary brachytherapy: A catheter containing a balloon and a tube with channels is placed into the breast, either under general anesthesia (the patient is unconscious) or local anesthesia (the area is numbed). The balloon is situated in the tumor bed and expanded to keep it securely in place. Radioactive pellets are then placed through the channels into the balloon. The treatment usually takes place in an outpatient setting twice a day for five days (or sometimes up to two weeks), and when it is finished, the device is removed and the patient is stitched up if necessary.

Interstitial brachytherapy: About one to two weeks after surgery, small hollow catheters are placed into the breast tissue around the tumor site using imaging guidance. Radioactive pellets are placed into the tubes for short times each day. This is typically done twice a day for five days.

The course of brachytherapy treatment is shorter than most EBRT treatment plans, making it a more convenient option. Initial research into intracavitary brachytherapy as the only radiation therapy after BCS, which is used more commonly than interstitial brachytherapy, shows comparable treatment outcomes to conventional whole-breast radiation treatments.

Since brachytherapy only treats a small area rather than the whole breast, it is not an appropriate treatment if cancer has spread beyond the tumor edges to surrounding tissue or into the lymph nodes. The treatment also requires leaving the delivery device or tubes in the breast during the course of the treatment, making it a more invasive procedure than EBRT.

How Is Radiation Therapy Used?

Women may receive radiation therapy at different stages as part of a treatment plan for various types of breast cancer, including DCIS, IBC and recurrent breast cancer. Doctors may use radiation:

• After lumpectomy (BCS) surgery to lower the risk of cancer returning
• After mastectomy surgery, particularly if cancer is present in a number of lymph nodes, the tumor is large (more than 2 inches) or if the chest wall muscles or skin contain cancer cells
• If cancer has spread (metastasized) into distant areas of the body
• If the cancer has recurred (returned) and radiation treatment was not given to treat the original malignancy

Radiation After Lumpectomy

Radiation after lumpectomy is used for early-stage breast cancer. It is generally a choice for women who want to conserve part of their breast and are willing to undergo the necessary postsurgery radiation treatments — although patients diagnosed with certain early-stage cancers may be candidates for one dose of IORT during surgery.

Doctors may recommend accelerated partial breast irradiation after a lumpectomy for patients with smaller malignancies that have not spread. However, most women who have a lumpectomy undergo whole breast radiation therapy in the weeks afterward. Boost radiation (one session of high-dose radiation) may also be given after lumpectomy if the risk of cancer recurrence is high.

Radiation After Mastectomy

Although radiation therapy is not used as often after mastectomy procedures as it is after lumpectomies, whole chest wall irradiation may be given to the scar region and entire chest wall if the tumor is large or the cancer has spread into nearby lymph nodes, muscle or skin. Sometimes, just chest wall (muscle, skin and mastectomy scar) radiation is administered if no lymph nodes are affected.

For women diagnosed with inflammatory breast cancer (IBC), radiation therapy after mastectomy is typically recommended as part of a multifaceted treatment plan, which has been shown to improve outcomes for this type of breast cancer. If a woman is also having breast reconstruction surgery, it is typically delayed until after radiation therapy is complete.

Radiation for Locally Advanced Breast Cancer

Radiation therapy is used after surgery to treat locally advanced breast cancer, including IBC, which tends to be a more aggressive form of cancer that is not typically diagnosed until the locally advanced stage.

Sometimes with IBC, the tumor does not shrink in response to breast cancer chemotherapy given before surgery. In this case, radiation therapy is also given before surgery to try to help shrink the tumor.

Since accelerated partial breast irradiation is typically only administered when breast cancer is in its early stages, women will likely receive whole breast radiation therapy for locally advanced breast cancer.

Radiation for Metastatic Breast Cancer

When cancer has spread to other organs, like the brain and spinal cord, it may cause symptoms that affect a patient’s quality of life. Radiation therapy is most commonly used alongside other treatments during this stage of cancer to help shrink tumors and relieve pain or other symptoms, such as headaches and dizziness. It may be administered to the bones, brain, spinal cord and chest wall.

Radiation for Breast Cancer Recurrence

Radiation therapy is only used for breast cancer recurrence if it was not part of the original cancer treatment plan. This is because patients who have already received the maximum recommended dose to the area may be at greater risk of side effects. If radiation was used to treat the original tumor, the doctor will recommend other treatment options like chemotherapy and immunotherapy instead of radiation.

If radiation was not used in the past, and the breast cancer returns:

• Near the spot of the original tumor, it is treated with mastectomy surgery if this was not already performed, followed by radiation therapy
• If mastectomy surgery was already performed, it is treated with the removal of the tumor if possible, followed by radiation therapy
• Regionally in nearby lymph nodes, it is treated by removing them and then radiation therapy
• In distant parts of the body, it is treated like metastatic breast cancer

Side Effects

Some women may experience mild, moderate or (less commonly) more severe side effects after radiation treatment for breast cancer. Others may have no side effects afterward.

Each person is different, and the extent and type of the side effects depend on a variety of factors, including the radiation type and dose, treatment length, the type of breast cancer being treated, combination therapies being given and the patient’s overall health.

Common side effects of radiation therapy for breast cancer may include:

• Breast soreness or pain
• Breast fluid buildup that causes swelling, called lymphedema
• Skin redness, irritation, peeling or darkening
• Fatigue
• Fluid collecting at the site (after brachytherapy) that causes a lump, called a seroma
• Breast tissue damage, bruising or infection after brachytherapy

Long-term side effects of radiation therapy for breast cancer may include:

• Breast skin that is either more or less sensitive and darker, firmer and thicker
• Larger breast skin pores
• Scar tissue that makes the breast smaller or lymphedema that makes the breast larger
• Rib fractures due to a weakened rib cage (which is rare)
• Arm and shoulder nerve damage
• Heart problems, such as irregular heartbeat, hardening of the arteries (arteriosclerosis) and heart valve injury
• Lung inflammation, called radiation pneumonitis

It is important for patients to tell their doctor right away if they experience these or other side effects so that the appropriate treatments may be given. Also, women who notice new breast changes a year or more after radiation treatment should immediately inform their doctor so that testing may be done to pinpoint the cause of these changes.

Will I Lose My Hair With Radiation Therapy for Breast Cancer?

If the doctor recommends radiation therapy to the breast, the patient will not lose hair on her head. This is because radiation therapy is a local treatment, meaning it will only cause hair loss from the body area being treated. In this case, small hairs on the breast, nipple or under the arms (for lymph node radiation) may fall out.

For women treated with radiation therapy for metastatic breast cancer that has spread to the brain, loss of hair on the head may be one of the side effects. Generally speaking, hair grows back after radiation, usually three to six months after treatment is complete. Sometimes a woman’s hair texture and color change after regrowth.

Hair loss is sometimes a difficult experience for women, and it is helpful to know what to expect and how to prepare. Talking to the care team about strategies to manage hair loss and regrowth often helps women navigate the mental, emotional and physical impacts of losing hair during cancer treatment.

Left Breast Cancer Radiation Effects on the Heart and Lungs

Although it is rare, radiation therapy may cause damage to lung tissue or heart issues. Women who have radiation therapy on the left breast (the side where the heart is located) are at a higher risk of developing heart problems than those receiving radiation on the right side.

A number of strategies may help reduce heart and lung problems after radiation therapy. Doctors administering radiation therapy may use proton therapy or intensity-modulated radiation therapy (IMRT) to reduce surrounding tissue damage. A technique called deep inspiration breath-hold (DIBH) also helps decrease the risks to the heart. Here, the woman lies on her back and takes a deep breath to fill up her lungs before the radiation treatment is administered. This moves the chest cavity farther from the heart to lower the chances of organ damage.

According to researchers in the Journal of Clinical Oncology, patients may also have some control over radiation therapy outcomes. Researchers analyzed results from several other studies and found that smokers who quit using tobacco significantly decreased the radiation therapy risks to their heart and lungs.

Radiation Therapy Versus Chemotherapy

In comparing radiation therapy and chemotherapy for breast cancer treatment:

• Chemotherapy uses anticancer drugs to destroy breast cancer cells, while radiation therapy uses high-energy particles
• Chemotherapy is not typically given for Stage 0 breast cancer (DCIS), while radiation therapy is almost always given after lumpectomy surgery at this stage
• Chemotherapy is typically given after lumpectomy for Stage 1 breast cancer only for larger tumors, while radiation therapy is almost always given after lumpectomy at this stage
• Chemotherapy may be given before and after surgery for Stage 2 breast cancer if the tumor is large, the cancer cells do not have an excess of a protein called HER2 or the cancer cells are positive for certain hormone receptors. Radiation therapy is almost always given after lumpectomy at this stage
• Chemotherapy is typically given before surgery for Stage 3 breast cancer (and sometimes after surgery), while radiation therapy is almost always given after surgery at this stage
• Chemotherapy is the first treatment given for inflammatory breast cancer before mastectomy surgery to help shrink the tumor, and it may also be given after surgery to destroy any remaining cancer. Radiation therapy is given after the surgery (although it may also be given before, if chemotherapy did not shrink the tumor)
• Chemotherapy may be used as the primary treatment for metastatic breast cancer, while radiation therapy is typically used to help manage symptoms at this stage

Both chemotherapy and radiation therapy may be used after breast cancer surgery for recurrent breast cancer that has come back.

Radiation Therapy Versus Hormone Therapy

Hormone receptor-positive (HR+) breast cancer has estrogen or progesterone receptors (or both) on the cells, which help the cancer cells grow. Hormone therapy for breast cancer uses drugs that block these receptors or lower levels of these hormones in the body to curb cancer cell growth.

Radiation therapy is used to treat several types and symptoms of breast cancer at every stage of the disease. Hormone therapy is also used to treat these same types of cancer at every stage of the disease, but only if those breast cancers are HR+.

City of Hope offers an array of state-of-the-art radiation therapy treatments to target different breast cancer types and stages, as well as taking patient goals into account. Women at the cancer treatment center are offered advanced treatment plans put together by world-class radiation oncologists, who aim to optimize treatment results while reducing healing times.