What is radiotherapy?

Radiotherapy uses high-energy x-rays to destroy cancer cells, while doing as little harm as possible to normal cells.

Normal cells can also be damaged by radiotherapy, which may cause side effects. But careful planning and newer ways of giving radiotherapy have reduced the risk of damage to healthy tissue and nearby organs. Cancer cells cannot repair themselves after radiotherapy, but normal cells usually can.

Radiotherapy reduces the risk of breast cancer coming back in the area it is given to. Some women may have radiotherapy as part of a research trial.

Radiotherapy after breast-conserving surgery

If you have breast-conserving surgery, your cancer doctor will recommend you have radiotherapy to the breast afterwards.

You usually start radiotherapy 4 to 6 weeks after surgery. If you are also having chemotherapy, radiotherapy is given after chemotherapy.

Some women may have a very low risk of the cancer coming back in the breast after surgery. If this happens, your cancer doctor may talk to you about the possibility of not having radiotherapy.

Before you decide if you should not have radiotherapy, talk about it carefully with your cancer doctor and specialist nurse. You need to fully understand the advantages and possible risks involved.

Radiotherapy after a mastectomy

You may still need radiotherapy to the chest after a mastectomy. This will depend on the risk of the cancer coming back in that area. You are more likely to have radiotherapy if:

  • the cancer was large
  • the cancer had spread to the lymph nodes in the armpit
  • there were cancer cells close to the edge of the removed breast tissue.

Radiotherapy to the lymph nodes

If the surgeon removed some lymph nodes from your armpit and they contained cancer cells, you may have radiotherapy to the rest of the lymph nodes.

Some women also have radiotherapy to the lymph nodes above the collarbone and lymph node close to the breastbone.

Having radiotherapy for breast cancer

You will have radiotherapy as an outpatient. It is usually given using equipment that looks like a large x-ray machine. You might hear it called external beam radiotherapy (EBRT).

You usually have radiotherapy as a series of short, daily treatments. These are called sessions. The treatments are given from Monday to Friday, with a rest at the weekend. The person who operates the machine is called a radiographer. They will give you information and support during your treatment.

You usually have radiotherapy for 3 weeks. Women who had breast-conserving surgery may have an extra dose (booster dose) to the area where the cancer was. Sometimes the booster dose is given at the same time as radiotherapy to the rest of the breast. Or it may be given at the end of the 3 weeks. This means you will need a few more treatments. Your doctor will tell you how many treatments you will need.

If you have radiotherapy to your left breast, you may be asked to take a deep breath and hold it briefly. This is called deep inspiration breath hold (DIBH). You do this at each of your planning and treatment sessions. It keeps you still and also moves your heart (which is behind your left breast) away from the treatment area. DIBH helps protect your heart during your treatment and reduces the risk of late effects.

Some women may have intensity-modulated radiotherapy (IMRT). This is another type of external beam radiotherapy. It shapes the radiotherapy beams and allows different doses of radiotherapy to be given to different areas. This means lower doses of radiotherapy are given to healthy tissue surrounding the tumour.

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

Getting support

Macmillan is also here to support you. If you would like to talk, you can:

Radiotherapy to part of the breast

Less commonly, some women are given radiotherapy to part of the breast instead of the whole breast. There are different ways of doing this.

Your cancer doctor or specialist nurse will explain if any of the following treatments are options for you. They will tell you what the possible side effects are and any risks involved.

It is important to have information about all your treatment options. They can explain how these treatments compare with external radiotherapy.

Internal radiotherapy

Some women are given radiotherapy from inside the body instead of to the whole breast. This is called brachytherapy and it is given over a shorter time.

Hollow tubes are put into the area where the cancer was removed from. Radioactive material is placed into the tubes. The radioactive material may be left in place for a few days. This is usually during a stay in hospital or given over a few sessions as an outpatient. The radioactive material is removed each time before you go home.

Intraoperative radiotherapy

This type of radiotherapy is also given from inside the body (internally), but during breast-conserving surgery.

After removing the cancer, your cancer doctor gives a single dose of radiotherapy to the same area. They give the radiotherapy from a special machine.

After intraoperative radiotherapy, you will not usually need any external radiotherapy to the rest of the breast. Some women may need a short course.

This type of radiotherapy (sometimes called intrabeam radiotherapy) is not suitable for everyone and is not widely available on the NHS. The National Institute for Health and Care Excellence (NICE) have approved its use, but not as standard treatment. NICE only covers England and Wales. Intrabeam radiotherapy should only be used in hospitals that already have intrabeam machines.

Planning your radiotherapy treatment

You will have a hospital appointment to plan your treatment. You will usually have a CT scan of the area to be treated. During the scan, you need to lie in the position that you will be in for your radiotherapy treatment.

Your radiotherapy team use information from this scan to plan:

  • the dose of radiotherapy
  • the area to be treated.

You may have some small, permanent markings made on your skin. The marks are about the size of a pinpoint. They help the radiographer make sure you are in the correct position for each session of radiotherapy.

These marks will only be made with your permission. If you are worried about them, talk to your radiographer.

Treatment sessions

Your radiographer will explain what happens during treatment. At the beginning of each session, they make sure you are in the correct position. If your muscles and shoulder feel stiff or painful, a physiotherapist can show you exercises that may help.

When you are in the correct position, your radiographer leaves the room and the treatment starts. The treatment itself is not painful and it only takes a few minutes.

The radiographers can see and hear you from outside the room. There is usually an intercom, so you can talk to them if you need to during your treatment.

During treatment, the radiotherapy machine may stop and move into a new position. This is so you can have radiotherapy from different directions.

Side effects of radiotherapy for breast cancer

Radiotherapy can cause side effects in the area of your body that is being treated. You may also have some general side effects, such as feeling tired.

After treatment finishes, it may be 1 to 2 weeks before side effects start getting better. After this, most side effects usually slowly go away.

Your cancer doctor, specialist nurse or radiographer will tell you what to expect. They will give you advice on what you can do to manage side effects. If you have any new side effects or if side effects get worse, tell them straight away.

Skin irritation

Your skin in the treatment area may get red, dry and itchy. Dark skin may get darker or have a blue or black tinge.

Your specialist nurse or radiographer will give you advice on looking after your skin. If it becomes sore and flaky, your doctor can prescribe creams or dressings to help this.

Skin reactions usually start to improve 2 weeks after radiotherapy finishes.

Here are some tips:

  • Do not put anything on your skin in the treatment area without checking with your specialist or radiographer.
  • Have cool or warm shower rather than a bath if you can. Turn away from the spray to protect the treated area.
  • Pat the area dry gently with a soft towel – do not rub.
  • Wear loose clothing that is less likely to irritate your skin.

You need to avoid exposing the treated area to the sun for at least a year after treatment finishes. Use suncream with a high sun protection factor (a minimum of 30 SPF) to protect your skin if it is exposed.


This is a common side effect that may last for up to 2 months after treatment. Try to get plenty of rest and pace yourself. Balance this with some physical activity, such as going for short walks, which will give you more energy.

Aches and swelling

You may have a dull ache or shooting pains in the treated area that last for a few seconds or minutes. You may also notice that the area becomes swollen. These effects usually improve quickly after treatment. You might still have aches and pains in the area after radiotherapy.

Late effects of radiotherapy for breast cancer

Radiotherapy to the breast may cause side effects that happen months or years after radiotherapy. They are called late effects.

Newer ways of giving radiotherapy are helping reduce the risk of these late effects happening. If you are worried about late effects, talk to your cancer doctor or specialist nurse.

The most common late effect is a change in how the breast looks and feels.

Radiotherapy can damage small blood vessels in the skin. This can cause red, spidery marks (telangiectasia) to show.

After radiotherapy, your breast may feel firmer and shrink slightly in size. If your breast is noticeably smaller, you can have surgery to reduce the size of your other breast.

If you had breast reconstruction, using an implant before radiotherapy, you may need to have the implant replaced.

It is rare for radiotherapy to cause heart or lung problems, or problems with the ribs in the treated area. This usually only happens if you had treatment to your left side.

Tell your cancer doctor if you notice any problems with your breathing, or have any pain in the chest area.

About our information

  • References

    Below is a sample of the sources used in our breast cancer information. If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk

    European Society for Medical Oncology. Primary breast cancer: ESMO clinical practice guidelines for diagnosis, treatment and follow-up. Annals of oncology 26 (supplement 5): v8–v30. 2015.

    Morrow M, et al. Chapter 79: malignant tumors of the breast. DeVita, Hellman and Rosenberg’s cancer: principals and practice of oncology (10th edition). Lippincott Williams and Wilkins. 2014.

    National Institute for Health and Care Excellence (NICE). Early and locally advanced breast cancer: diagnosis and management. July 2018.

    Scottish Intercollegiate Guidelines Network. SIGN 134. Treatment of primary breast cancer: a national clinical guideline. September 2013.

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Rebecca Roylance, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

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