Help us to stop bowel cancer


Radiotherapy is a possible treatment for rectal cancer, where there is a risk of the cancer coming back after surgery. It is not usually used to treat bowel cancer.

You may have radiotherapy to try to cure your cancer, either alone or together with surgery or chemotherapy (chemoradiation). If your cancer cannot be cured, you may have radiotherapy to relieve your symptoms. This is called palliative radiotherapy.

There are two main ways of having radiotherapy – externally and internally.

Doctors also use radiotherapy to treat bowel cancer that has spread to other parts of the body. There are two specialised types of treatment - stereotactic radiotherapy and selective internal radiotherapy (SIRT). 

External radiotherapy

External radiotherapy uses high energy X-ray beams to kill cancer cells. Your healthcare team may offer you radiotherapy before surgery if there is a risk of the cancer coming back in the same place.

You may have a short course of five radiotherapy sessions in the week before your operation.

If you have a tumour that has grown through the bowel wall and may not be completely removed with surgery alone,  you may need a longer course of radiotherapy. This is often combined with chemotherapy (chemoradiation) and takes five to six weeks. In this case, you would have a few week breaks between radiotherapy and surgery, to give the tumour time to shrink.

Doctors sometimes use radiotherapy to treat rectal cancer that cannot be cured. This is called palliative radiotherapy. The treatment shrinks the cancer and relives symptoms such as pain.


Radiotherapy together with chemotherapy (chemoradiation) shrinks the tumour, making it easier to remove. It also reduces the risk of cancer coming back in the same place, compared with radiotherapy alone. But chemoradiation causes more short-term side effects, like loose and runny poo (diarrhoea). 

If you didn’t have radiotherapy or chemotherapy before surgery, your specialist may offer you chemoradiation after surgery if there is a high risk of the cancer coming back.

Recently, researchers have suggested that up to one in five people treated with chemoradiation can be cured of their cancer without surgery. This is not standard treatment yet and needs more research.  Specialists aren’t yet able to tell who will benefit from this treatment and who will not.

Internal radiotherapy

Your healthcare team may offer you internal radiotherapy (brachytherapy), depending on the size of the cancer and where it is in the rectum.

Brachytherapy involves placing a source of radiation inside the rectum for a few minutes. There are two types of brachytherapy used to treat rectal cancer – low-energy contact X-ray brachytherapy and high dose rate brachytherapy.

Low-energy contact X-ray brachytherapy (Papillon technique) uses X-rays to cure early rectal cancer or stop it spreading. This treatment may be an option for people who cannot have surgery. There isn’t much evidence to show how well it works for people who can have surgery but have chosen not to. Your healthcare team can give you more information about the benefits and risks of this treatment.

The aim of high dose rate (HDR) brachytherapy is to shrink the cancer before surgery. There isn’t enough evidence to show how well it works, either alone or together with external radiotherapy. If this is a treatment option for you, your healthcare team will explain the benefits and risks.

Side effects

All treatments carry a risk of side effects. Your healthcare team should give you written information about the possible side effects. But they won’t be able to tell you in advance which side effects you will get or how long they will last.

If you are having two or more treatments together, the side effects may be worse.

At your hospital appointments, your healthcare team will ask you about the side effects you’re getting. You might want to keep a diary to help you remember the details.

Possible short-term side effects of radiotherapy include:

  • Sore skin
  • Bowel problems
  • Bladder problems
  • Sexual problems
  • Tiredness
  • Difficulty sleeping.

These side effects often get better in the first few months after you finish treatment. But some people have long-term or new side effects that do not get better without support from the healthcare team.

You may have new or long-term changes to the way your bowel works, such as loose and runny poo (diarrhoea), having to open your bowels more or less often than before, being woken from sleep to poo, having less warning to get to a toilet in time or being unable to control the bowel and having accidents.

Tell your healthcare team as soon as possible if you have any new or ongoing side effects. You may need to have some tests to find out what is causing them. Your healthcare team can give you treatments that can improve these side effects.

Radiotherapy may damage the bones in your pelvis (the area between your hips) and can lead to fractures. Tell your healthcare tea if you have any pain or stiffness in your pelvis or back.

Radiotherapy can also irritate your bladder and can affect your sexual function

Radiotherapy usually causes infertility. But you should still use contraception during treatment and for about a year afterwards in case there is any chance of pregnancy. Radiotherapy can damage sperm and eggs and harm a developing baby.

Many people living with bowel cancer worry about the cancer coming back and about returning to normal life after treatment. Your healthcare team can offer you support. Read our page on worries about the future for more information. 

If you have any new symptoms or have any worries, speak to your healthcare team who can advise you where to find further information or support.

More information

Macmillan Cancer Support has information on radiotherapy for rectal cancer and its side effects. Also for information on late effects of pelvic radiotherapy.

Cancer Research UK provides information on internal and external radiotherapy for rectal cancer.

National Institute for Health and Care Excellence (NICE) provides patient information on high dose rate brachytherapy and low-energy contact X-ray brachytherapy.

Pelvic Radiation Disease Association is a patient-run charity providing support and information for people who have had pelvic radiotherapy.


Updated March 2016. Due for review March 2018