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Partial breast radiation therapy - external beam

Partial breast radiation therapy uses high-powered x-rays to kill breast cancer cells. This type of treatment does not target the entire breast, rather just the area around where the original cancer was located, sparing some normal tissue. It is also called accelerated partial breast radiation (APBI).

A standard course of whole breast directed external beam breast treatment takes 3 to 6 weeks. APBI can be accomplished in as little as 1 to 2 weeks. APBI targets a high dose of radiation only on or near the area where the breast tumor was removed. It avoids exposing the surrounding tissue to radiation.

There are three common approaches for APBI:

  • External beam, the topic of this article
  • Brachytherapy (inserting radioactive sources into the breast)
  • Intraoperative radiation (delivering radiation at the time of surgery in the operating room)


Radiation therapy is usually delivered on an outpatient basis, except for intraoperative radiation therapy.

Two common techniques are used for partial breast external beam radiation treatment:

  • Three dimensional conformal external beam radiation (3DCRT)
  • Intensity-modulated radiation therapy (IMRT)

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

  • The doctor will put small marks on your skin. These marks ensure that you are correctly positioned during your treatments.
  • These marks will either be ink marks or a permanent tattoo. Do not wash ink marks off until your treatment is finished. They will fade over time.

The treatment is usually given 5 days a week for anywhere from 2 to 6 weeks. It may sometimes be given twice a day (usually with 4 to 6 hours between sessions).

  • During each treatment session you will lie on a special table, either on your back or your stomach.
  • The technicians will position you so the radiation targets the treatment area.
  • You may be asked to hold your breath while the radiation is being delivered. This helps limit how much radiation your heart receives.
  • Most often, you will receive radiation treatment for between 1 and 5 minutes. You will be in and out of the cancer center within 15 to 20 minutes on average.

You are not radioactive after these radiation treatments. It is safe to be around others, including babies and children.

Why the Procedure is Performed

Experts learned that certain cancers are most likely to return the location of the original cancer. Therefore, in some cases, the whole breast may not need to receive radiation. Partial breast irradiation only treats some but not all of the breast, focusing on the area where the cancer is most likely to return, usually around the surgical cavity.

This accelerated partial breast radiation speeds up the process.

APBI is used to prevent breast cancer from coming back. When radiation therapy is given after breast-conserving surgery, it is called adjuvant (additional) radiation therapy.

APBI may be given after lumpectomy or partial mastectomy (called breast-conserving surgery) for:

  • Ductal carcinoma in situ (DCIS)
  • Stage I or II breast cancer

Before the Procedure

Tell your health care provider what medicines you are taking.

Wear loose fitting clothes to the treatments.

After the Procedure

Radiation 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. Radiation can have short-term (acute) or long-term (later) side effects.

Short-term side effects can begin within days or weeks after treatment begins. Most side effects of this type go away within 4 to 6 weeks after treatment ends. Most common short-term effects include:

  • Breast redness, tenderness, sensitivity
  • Breast swelling or edema
  • Breast infection (rare)

Long-term side effects may begin months or years after treatment and may include:

  • Decreased breast size
  • Increased firmness of breast
  • Skin redness and discoloration
  • In rare cases, rib fractures, heart problems (more likely for left breast radiation), or lung inflammation (called pneumonitis) or scar tissue affecting breathing
  • The development of second cancer in the breast or chest years or even decades later
  • Arm swelling (edema) -- more common if lymph nodes were surgically removed and if the armpit area was treated with radiation

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

Outlook (Prognosis)

Partial breast radiation following breast conservation therapy reduces the risk of cancer coming back, and possibly even death from breast cancer.

Alternative Names

Carcinoma of the breast - partial radiation therapy; Partial external beam radiation - breast; Intensity-modulated radiation therapy - breast cancer; IMRT - breast cancer WBRT; Adjuvant partial breast - IMRT; APBI - IMRT; Accelerated partial breast irradiation - IMRT; Conformal external beam radiation - breast


National Cancer Institute website. Breast cancer treatment (PDQ) - health professional version. Updated February 9, 2023. Accessed February 28, 2023.

National Cancer Institute website. Radiation therapy and you: support for people who have cancer. Updated April, 2021. Accessed November 18, 2022.

Shah C, Harris EE, Holmes D, Vicini FA. Partial breast irradiation: accelerated and intraoperative. In: Bland KI, Copeland EM, Klimberg VS, Gradishar WJ, eds. The Breast: Comprehensive Management of Benign and Malignant Diseases. 5th ed. Philadelphia, PA: Elsevier; 2018:chap 51.

Review Date 7/23/2022

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 02/28/2023.

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