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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.

Internal radiotherapy

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. The tube is 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 later.

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 for rectal cancer 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. Chemotherapy and radiotherapy given together are called 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 so that it is close to the tumour. The radiographer may take an X-ray to check that 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 compared to external radiotherapy. 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
  • Narrowing (stenosis) of the back passage
  • A hole (fistula) developing between the rectum and the bladder or vagina

Radiotherapy after surgery

If you haven't had radiotherapy before your operation for rectal cancer, your surgeon and cancer specialist may want you to have some external radiotherapy afterwards. This may be because

  • 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 (chemoradiation).


Planning treatment

Before you begin your treatment, the radiotherapy team carefully plan your external beam radiotherapy. This means working out how much radiation you need to treat the cancer and exactly where you need it. Your planning appointment may take from 15 minutes up to a couple of hours. You will have a planning CT scan. The scan shows the cancer and the structures around it.

The 360° photo is of a CT scanner. You can use the arrows to look around the room.

You lie on the scanner couch with the treatment area exposed. The radiographers will put some markers on your skin. You need to lie very still. Once you are in position the radiographers move the couch up and through the scanner. The scanner is a doughnut shape. The radiographers leave the room and the scan starts. It takes up to 5 minutes. You won't feel anything. The radiographers watch from the next door room.

Before the planning appointment you may also have other scans, such as MRI scans or PET scans. Your treatment team can feed the other scans into the planning scanner.

Ink marks

Once the treatment team has planned your radiotherapy, they may put ink marks on your skin to make sure they treat exactly the same area every day. They may also make pin point sized tattoo marks in these areas. We have information about radiotherapy skin markings.

After your planning session

You may have to wait a few days or up to 2 weeks before you start treatment. During this time the physicists and your radiotherapy doctor decide the final details of your plan. Your doctor will plan the areas that need treatment and outline areas to limit the dose to or avoid completely. They call this contouring. Then the physicists and staff called dosimetrists plan the treatment very precisely using advanced computers.


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.

Radiotherapy machines are very big. The machine may be fixed in one position or able to rotate around your body to give treatment from different directions. Before your first treatment your radiographers will explain what you will see and hear. The treatment rooms usually have docks for you to plug in music players. So you can listen to your own music.

You can't feel radiotherapy when you actually have the treatment. It takes anything from 1 minute to several minutes. It is important to lie in the same position each time, so the radiographers may take a little while to get you ready.

A photo of a linear accelerator, which gives radiotherapy

Once you are in the right position the staff leave you alone in the room for a few minutes. They watch you carefully through a window or on a closed circuit television screen. They may ask you to hold your breath or take shallow breaths during the treatment.

Our page about having external radiotherapy has a video about having radiotherapy that you may want to watch.

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 in general, look at our main radiotherapy section. It tells you about

We have information about the side effects of rectal radiotherapy.

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.

You can phone the Cancer Research UK nurses on freephone 0808 800 4040. The lines are open from 9am to 5pm, Monday to Friday. They will be happy to answer any questions that you have.

Our general organisations page gives details of people who can provide information about radiotherapy. Some organisations can put you in touch with a cancer support group. Our cancer and treatments reading list has information about books, leaflets and other resources about radiotherapy treatment.

If you want to find people to share experiences with online, you could use Cancer Chat, our online forum.

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Updated: 20 August 2014