Radiotherapy treats cancer by using high-energy rays to destroy the cancer cells, while doing as little harm as possible to normal cells.

Radiotherapy is often used after surgery for breast cancer. It may occasionally be used before, or instead of, surgery.

If part of the breast has been removed (lumpectomy or segmental excision), radiotherapy is usually given to the remaining breast tissue, to reduce the risk of the cancer coming back in that area.

After a mastectomy, radiotherapy to the chest wall may be given if your doctor thinks there is a risk that any cancer cells have been left behind.

If a few lymph glands have been removed and these contained cancer cells, or if no lymph glands have been removed, radiotherapy may be given to the armpit to treat the remaining lymph glands. If all the lymph glands have been removed from under the arm, radiotherapy to the armpit is not usually needed.

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

A course of radiotherapy for breast cancer may last from 3–6 weeks. It is usually given as an outpatient.

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

Planning is a very important part of radiotherapy, and makes sure that it is as effective as possible. It may take a few visits. On your first visit to the radiotherapy department, you will be asked to have a CT scan or lie under a machine called a simulator, which takes x-rays of the area to be treated. The treatment is planned by a cancer specialist (clinical oncologist). Marks are usually drawn on your skin to help the radiographer (who gives you your treatment) to position you accurately and to show where the rays will be directed. These marks must stay throughout your treatment, and permanent marks (like tattoos) may be used. These are tiny, and will only be done with your permission. It may be a little uncomfortable while being done.

The radiotherapy is normally given to the whole breast area. Some women may have an extra dose given to the area of the breast where the cancer was. This is known as a booster dose.

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 will be left alone in the room but you will be able to talk to the radiographer who will be watching you from the next room. Radiotherapy is not painful but you do have to lie still for a few minutes while the treatment is being given.

If you are going to have radiotherapy, you will need to be able to get your arm into position 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 feel easier.

Radiotherapy to the breast sometimes causes side effects such as reddening and soreness of the skin, feeling sick (nausea) and tiredness. These side effects gradually disappear once your course of treatment has finished. The tiredness may continue for some months.

Perfumed soaps, creams or deodorants may irritate the skin and should not be used during the treatment. At the beginning of your treatment you will be given advice on how to look after the skin in the area being treated.

Radiotherapy may make the breast tissue feel firmer. Over a few months or years the breast may shrink slightly. The radiotherapy may also, rarely, leave small red marks on the skin, which are due to tiny broken blood vessels. For many women, however, the appearance of the breast is very good.

Radiotherapy to the breast can sometimes lead to long-term side effects, such as nerve pain, tingling, and weakness or numbness in the arm and hand (peripheral neuropathy). Other rare side effects can include breathlessness (due to the effect of radiotherapy on the lung), and weakening of the ribs in the treatment area. However, these long-term effects are very rare.

If you are worried about the risk of developing particular side effects from radiotherapy, you can speak to your clinical oncologist (radiotherapist).

After your radiotherapy treatment, let your doctor know straight away if you have any arm or rib pain, or breathlessness.

We have information about the possible long-term side effects of radiotherapy for breast cancer.