(Courtesy of Macmillan Cancer Support) 

Radiotherapy for breast cancer

Radiotherapy treats cancer by using high-energy rays to destroy the cancer cells, while doing as little harm as possible to normal cells. It decreases the risk of breast cancer coming back in the breast or chest area (local recurrence). 

Radiotherapy after surgery to conserve the breast

If you’ve had a lumpectomy or a wide local excision, (insert link) you will be advised to have radiotherapy to the breast afterwards.

If your cancer specialist thinks the risk of local recurrence is high, you may have an extra dose to the area of the breast where the cancer was (booster dose).

You’ll usually start radiotherapy about 6-8 weeks after your surgery unless you’re having chemotherapy. Radiotherapy is usually given after chemotherapy has finished.

Radiotherapy after a mastectomy

If there’s an increased risk of your cancer coming back in the same area after a mastectomy, your cancer specialist will advise you to have radiotherapy to the chest. They may advise this if:

  • you had a large cancer
  • the cancer was high-grade
  • four or more lymph nodes in the armpit contained cancer cells
  • there were cancer cells close to the edge of the removed breast tissue.

Radiotherapy to lymph nodes in the armpit

If the cancer has spread to the lymph nodes but only some were removed, you’ll usually have radiotherapy to the remaining nodes. If you had all the lymph nodes in your armpit removed, you won’t need to have radiotherapy as well.

Radiotherapy can be internal or external. The following section is about external radiotherapy.

External radiotherapy

The treatment is given in the hospital radiotherapy department as a series of short daily sessions. Each treatment takes 10–15 minutes and they are usually given Monday–Friday with a rest at the weekend. Your doctor will discuss the treatment and possible side effects with you.

A course of radiotherapy for breast cancer is usually given for three weeks. Some women may be given radiotherapy in different ways or over a different timescale as part of a clinical trial.
Radiotherapy is normally given to the whole breast area. Depending on the risk of the cancer coming back, it may also be given to areas of lymph nodes close to the breast. This includes the armpit and the area just above the collarbone and by the breastbone (sternum).

External radiotherapy does not make you radioactive and it is safe for you to be with other people, including children, after your treatment.

Planning radiotherapy

To make sure that the radiotherapy is as effective as possible, it has to be carefully planned. Planning ensures the radiotherapy rays are aimed precisely at the cancer and cause the least possible damage to the surrounding healthy tissues. The treatment is planned by a specialist doctor known as a clinical oncologist. Planning is important and may take a few visits.

On your first visit to the radiotherapy department, you’ll have a CT (computerised tomography) scan taken of the area to be treated. A CT scan takes a series of x-rays which build up a three dimensional picture of the area. At the same time therapy radiographers will take measurements from you which are needed for treatment planning. This session will usually take about 45–60 minutes.

Sometimes you may also need to go to the hospital’s scanning department to have an MRI scan. This uses powerful magnetic fields to give a detailed picture of part of your body, which can give additional useful information.

The radiographer’s measurements and the information from the scans are fed into the radiotherapy planning computer to help your doctors plan your treatment more precisely.

Marks may be drawn on your skin to help the radiographer, who gives you your treatment, to position you accurately and to show where the rays are to be directed. These marks must stay visible throughout your treatment, but they can be washed off once your course of treatment is over. At the beginning of your radiotherapy you’ll be told how to look after the skin in the area to be treated.


You’ll need to be able to position your arm so that the radiotherapy machine can give the treatment effectively. Sometimes your muscles and shoulder joint may feel stiff. If you can’t move your shoulder normally, it may be painful or difficult to give the treatment. A physiotherapist may teach you some exercises to make the position for treatment more comfortable.

Treatment sessions

At the beginning of each session of radiotherapy, the radiographer will position you carefully on the couch and make sure you are comfortable. During your treatment you’ll be alone in the room, but you can talk to the radiographer who will watch you from the next room. Radiotherapy is not painful, but you will have to lie still for a few minutes during the treatment.

Positioning the radiotherapy machine.

Side effects of radiotherapy

Radiotherapy to the breast sometimes causes side effects such as:

  • reddening and soreness of the skin (Common towards the end of the treatment only)
  • tiredness (Common but mild)
  • feeling sick (nausea) (Rare and usually mild)

You may develop side effects over the course of your treatment. These usually disappear gradually over a month or so after treatment is finished. Your doctor, nurse or radiographer will discuss this with you so you know what to expect. Let them know about any side effects you have during or after treatment. There are often things that can be done to help.