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Radiation therapy is treatment with high-energy rays (such as x-rays) or particles to kill cancer cells. Radiation therapy may be used to kill cancer cells remaining in the breast, chest wall, or underarm area after surgery or, less often, to shrink a tumor before surgery. Radiation to the breast is often needed after breast-conserving surgery. It is usually given after any chemotherapy. Radiation is also used to treat cancer that has spread to other areas, for example to the bones or brain.

Radiation therapy can be given in 2 main ways.

External beam radiation

In external beam radiation, the radiation is focused on the area being treated from a machine outside the body. This is the most common type of radiation used for treating breast cancer. It is much like getting a regular x-ray but the radiation is more intense.

For women getting radiation after breast conserving surgery or mastectomy, treatment is usually given 5 days a week (Monday through Friday) in an outpatient center. It lasts about 5 to 6 weeks. With some newer methods, treatments may only go over a few weeks or even less time. This is called accelerated breast irradiation.

Each treatment lasts a few minutes. The treatment itself is painless. Ink marks or small tattoos may be put on your skin. These will be used as a guide to focus radiation on the right area, which includes the breast or chest and the area under the arm. Check with your health care team if the marks they use will be permanent.

Possible side effects of external beam radiation: The main short-term side effects of radiation to the breast are:

  • Swelling and heaviness in the breast
  • Skin changes over the treated area, ranging from mild redness to blistering and peeling
  • Feeling very tired
  • The breast may feel hard for a time

Most skin changes get better within a few months. Changes to the breast tissue take longer to go away.

Radiation can lead to problems with breast reconstruction.

Radiation to the breast or lymph nodes under the arm also lead to some long-term side effects, such as damage to some of the nerves to the arm and long-term arm swelling (called lymphedema). More information about side effects of radiation to treat breast cancer can be found in the Breast Cancer detailed guide. You can get more information on lymphedema in Lymphedema: What Every Women With Breast Cancer Should Know.


Another way to give radiation to the breast is to place radioactive seeds (pellets) into the breast tissue. This may be given along with external beam radiation to add an extra “boost” of radiation to the tumor for women who have had breast conserving surgery. Some women may get brachytherapy as the only source of radiation (instead of radiation to the whole breast). So far the results have been good, but it may not be as good as external beam radiation long-term.

There are different types of brachytherapy. The most common type used to treat breast cancer is called intracavitary brachytherapy. A device is put into the space left from breast-conserving surgery, and then a source of radiation is put in the device for a short time and then removed. Treatments are given twice a day for 5 days.

Possible side effects of brachytherapy include redness, bruising, breast pain, infection, and a breakdown of an area of fat tissue inside the breast. As with whole breast radiation, weakness and fracture of the ribs can also occur.

Last Medical Review: 09/09/2014
Last Revised: 01/14/2016