This type of radiation is delivered by an x-ray machine that delivers a precise area of radiation either to the whole breast, or the chest wall (if done after mastectomy). Sometimes, radiation will also target the lymph nodes in the armpit or neck area or under the breast bone.

You may receive radiation treatment either in a hospital or in a private outpatient radiation center. You will go home after each treatment. A typical course of treatment is given 5 days a week for 3 to 6 weeks. During treatment, the treatment beam is on for only a few minutes. Often each treatment is scheduled the same time each day for your convenience. You are not radioactive after treatment.

Before you have any radiation treatment, you will meet with the radiation oncologist. This is a doctor who specializes in radiation therapy.

Before radiation is delivered there is a planning process called a "simulation" where the cancer and normal tissues are mapped. Sometimes the doctor will recommend small skin marks called "tattoos" to help line you up and improve the accuracy of the radiation therapy.

• Some centers use ink tattoos. These marks are permanent, but are most often smaller than a mole. These cannot be washed off, and you can bathe and shower normally. After treatment, if you want the marks removed, laser or surgery can be used.
• Some centers use marks that can be washed off. You may be asked not to wash the area during treatment and the marks may need to be touched up before each treatment session.

During each treatment session:

• You will lie on a special table, either on your back or your stomach and the machine will rotate around you.
• The technicians will position you so the radiation targets the treatment area.
• Sometimes alignment x-rays or scans are taken before treatment to make sure you are lined up in the right treatment position.
• Some centers use a machine that delivers radiation at certain points of your breathing cycle. This can help limit radiation to the heart and lungs. You may be asked to hold your breath while the radiation is being delivered. You may have a mouthpiece to help regulate your breathing.
• Most often, you will receive radiation treatment for between 1 and 5 minutes. Each day you will be in and out of the treatment center in less than 20 minutes on average.

After surgery, cancer cells may remain in the breast tissue or lymph nodes. Radiation can help kill the remaining cancer cells. When radiation is delivered after surgery is performed, it is called adjuvant (additional) treatment.

Adding radiation therapy can kill the remaining cancer cells and lower the risk of the cancer growing back.

Whole breast radiation therapy may be given for several different cancer types:

• For ductal carcinoma in situ (DCIS)
• For stage I or II breast cancer, after lumpectomy or partial mastectomy (breast-conserving surgery)
• For more advanced breast cancer, sometimes even after full mastectomy to reduce risk of recurrence
• For cancer that has spread to local lymph nodes (in the neck or armpit or chest)
• For widespread breast cancer, as a palliative treatment to relieve symptoms

Tell your health care provider what medicines you are taking.

Wear loose-fitting clothes to the treatments. You may be asked to wear a special bra.

You are not radioactive after radiation treatments. It is safe to be around others, including babies or children. As soon as the machine stops, there is no more radiation in the room.

Radiation therapy, like any cancer therapy, can also damage or kill healthy cells. The death of healthy cells can lead to side effects. These side effects depend on the dose of radiation and how often you have the therapy.

Side effects can develop early during treatment (within a few weeks) and be short-lived, or they may be more lasting long-term side effects. Late side effects can happen months or years later.

Early side effects that can begin 1 to 3 weeks after your first treatment may include:

• You may develop some breast swelling, tenderness, and sensitivity.
• Your skin over the treated area may turn red or darker in color, peel, or itch (much like a sunburn).

Most of these changes should go away about 4 to 6 weeks after the radiation treatment is over.

Your provider will explain care at home during and after radiation treatment.

Late (long-term) side effects may include:

• Decreased breast size
• Increased firmness of breast
• Skin redness and discoloration
• Swelling in the arm (lymphedema) in women who have had nearby lymph nodes removed
• In rare cases, rib fractures, heart problems (more likely for left breast radiation) or damage to underlying lung tissue
• Development of a second cancer in the treatment area (the breast, ribs, or muscles of the chest or arm)

Whole breast radiation therapy following breast-conserving surgery reduces the risk of cancer coming back and reduces the risk of death from breast cancer.

Breast cancer - radiation therapy; Carcinoma of the breast - radiation therapy; External beam radiation therapy (EBRT) - breast; Intensity-modulated radiation therapy - breast cancer; Radiation - whole breast; WBRT; Breast radiation - adjuvant; Breast radiation

Bazan JG, Alex Y, Jhawar SR. Postmastectomy radiation therapy. In: Klimberg VS, Gradishar WJ, Bland KI, Korourian S, White J, Copeland EM, eds. Bland and Copeland’s The Breast. 6th ed. Philadelphia, PA: Elsevier; 2024:chap 46.

Davidson NE. Breast cancer and benign breast disorders. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 183.

National Cancer Institute website. Breast cancer treatment (PDQ) - health professional version. www.cancer.gov/types/breast/hp/breast-treatment-pdq. December 6, 2024. Accessed January 3, 2025.

National Cancer Institute website. Radiation therapy and you: support for people who have cancer. www.cancer.gov/publications/patient-education/radiation-therapy-and-you. Updated April 2021. Accessed October 25, 2024.

Updated by: David Herold, MD, Radiation Oncologist in Jupiter, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. Editorial update 1/3/2025.