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Radiotherapy for rectal cancer

Radiotherapy uses high energy rays to kill cancer cells. Doctors often use it to treat cancer in the back passage (rectum). You may have external radiotherapy before or after surgery, to lower the risk of the cancer coming back later. Before surgery radiotherapy may also shrink tumours and make them easier to remove. Usually, you have radiotherapy at the same time as chemotherapy. 5FU (fluorouracil) or capecitabine chemotherapy makes cancer cells more sensitive to radiation. You usually have external radiotherapy every Monday to Friday for 1 to 5 weeks, depending on the size and type of cancer and the hospital treating you.

A newer treatment for some rectal cancers is high dose rate (HDR) internal radiotherapy (called brachytherapy). You have a tube containing radioactive material put into your rectum, close to the tumour and left in place for a short time to deliver the radiation dose. You usually have a sedative before this treatment to help you relax. You can normally go home afterwards. You then have surgery a few weeks after this treatment.

There is more information in our radiotherapy section.

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About bowel cancer radiotherapy

Radiotherapy uses high energy rays to kill cancer cells. Doctors don't often use it to treat cancer in the large bowel (colon cancer). But they often use it to treat cancer that started in the back passage (rectum). Usually, you have this treatment at the same time as 5FU (fluorouracil) or capecitabine chemotherapy. The chemotherapy makes the cancer cells more sensitive to radiation.

To treat rectal cancer, you may have radiotherapy

Another page in this section tells you about radiotherapy to treat the symptoms of advanced bowel cancer.


External radiotherapy before surgery

Doctors use radiotherapy before surgery to

  • Lower the risk of the cancer coming back after surgery
  • Shrink tumours and make them easier to remove completely

If your tumour can be operated on, you are likely to have a short course of 5 radiotherapy treatments in the week before surgery. This will kill many of the cancer cells. And the treatment also makes it less likely that any cancer cells will spread at the time of your surgery. You may have 5FU (fluorouracil) or capecitabine chemotherapy at the same time as the radiotherapy. Doctors call chemotherapy and radiotherapy given together chemoradiation.

If you have a large tumour, you may need a longer course of treatment before surgery. The treatment may last up to 5 weeks. You may have chemotherapy at the same time. You usually have surgery a few weeks after this sort of radiotherapy, to give the tumour time to shrink.


Internal radiotherapy before surgery

A newer treatment for some cancers in the middle or lower third of the rectum is high dose rate (HDR) internal radiotherapy. This treatment is called brachytherapy. You usually have it before surgery. The aim is to shrink the tumour so that it is easier to completely remove it.

You normally have a sedative before the procedure to help you to relax. The doctor gently pushes a tube through your anus into your rectum and places it close to the tumour. The radiographer may take an X-ray to check the tube is in the right place. The tube is attached to the brachytherapy machine. The radioactive source moves from the machine into the tube by remote control. It is left in place to deliver the correct dose of radiation to the tumour. The staff leave the room during the treatment, which may take about 10 to 15 minutes. They can see you on a TV monitor and talk to you through an intercom. Once the treatment is over, the radioactive source moves back into the machine and the tube is taken out. Then you can usually go home. As you have had sedation you will need a friend or relative with you. You normally have surgery a few weeks later.

Results from studies seem to show that people who have internal radiotherapy are less likely to need a colostomy than people who have external radiotherapy. But it is not clear whether internal radiotherapy helps people to live any longer. The National Institute for Health and Care Excellence (NICE) guidelines say the procedure is safe and works well enough to be used for rectal cancer. But we need further research to see how well it works in the long term. 

Everyone who has internal radiotherapy for rectal cancer treatment must be closely monitored afterwards. Possible side effects of the procedure include making a hole in the rectum or bladder, tightening (stenosis) of the back passage, or a hole (fistula) developing between the rectum and the bladder or vagina.


Radiotherapy after surgery

If you haven't had radiotherapy before your operation, your surgeon and cancer specialist may want you to have some external radiotherapy afterwards if

  • Your cancer was difficult to remove
  • Your surgeon thinks some cancer cells may be left behind
  • Your cancer had grown through the bowel wall or spread to nearby lymph nodes

Radiotherapy after surgery is called adjuvant radiotherapy (pronounced ad-joo-vant). You usually have this type of radiotherapy treatment over 4 to 5 weeks. You have treatment from Monday to Friday, so you have 20 to 25 treatments in total. Each individual treatment is called a fraction. Giving the treatment in small fractions reduces the side effects to healthy tissues. You may have chemotherapy with radiotherapy. Doctors call this chemoradiation.


Planning treatment

Radiotherapy treatment is carefully planned. During your planning appointment, you lie under a specialised CT scanning machine. The doctor uses the machine to see the cancer from all sides (3 dimensionally or 3D).

Picture of a simulator

Using information from the machine and other scans, your treatment team work out exactly where to give the treatment to

  • Target all of the tumour and a border of tissue around it, where there are most likely to be cancer cells
  • Avoid as much of the surrounding healthy body tissue as possible

For external radiotherapy, you may have marks made on your skin during the planning session. The radiographer uses these skin marks to line up the radiotherapy machine every day when you have your treatment. Don't worry if they wear off a bit. Your radiographer can draw them again. They need to be very accurate so don't try to draw them on again yourself. Sometimes the radiographer replaces the skin marks with a few pin prick tattoos.


Having external radiotherapy

You have radiotherapy in the hospital radiotherapy department.

For external radiotherapy, you usually have treatment once a day from Monday to Friday. You then have a rest over the weekend. The treatment before surgery for rectal cancer lasts from 1 to 5 weeks, depending on the size and type of your cancer and the hospital treating you.

If you are having radiotherapy after surgery, the course of treatment is usually 4 to 5 weeks, but may be up to 6 or 7 weeks long.

With external radiotherapy, the actual treatment only takes a few minutes. The radiographer positions you on the treatment table and makes sure you are comfortable. You will be left alone while you have your treatment but the radiographers can hear you through an intercom. You can talk to them or ask them questions.

Radiotherapy doesn't hurt. You won't be able to feel it but you need to lie very still for the few minutes that you have your treatment.

External radiotherapy doesn't make you radioactive. It is perfectly safe to be with other people, including children, throughout your course of treatment.


More information about radiotherapy

To find out more about radiotherapy, look at our main radiotherapy section. It tells you about

There are books and booklets about radiotherapy, some of which are free. Look in the treatment reading list for details.

We also have information about the latest research into radiotherapy for rectal cancer.

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Updated: 9 December 2011