Radiotherapy for rectal cancer | Cancer Research UK
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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 might have external radiotherapy before or after surgery, to lower the risk of the cancer coming back. Before surgery, radiotherapy may also shrink tumours and make them easier to remove. Usually, you have radiotherapy at the same time as chemotherapy. Fluorouracil (5FU) 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). Your doctor puts a tube put into your rectum, close to the tumour. They connect the tube is to the brachytherapy machine which gives 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.

Another type of internal radiotherapy is called contact radiotherapy or papillon treatment. It uses low dose X-rays to treat the cancer. It is only used for small, early cancers and if you are unable to have surgery. At the moment this treatment is only available in a few hospitals.

There is more information about having radiotherapy in our main 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 do often use it to treat cancer that started in the back passage (rectum). 

Usually, you have this treatment at the same time as fluorouracil (5FU) or capecitabine chemotherapy. The chemotherapy makes the cancer cells more sensitive to radiation.

To treat rectal cancer, you might have radiotherapy

  • Before surgery (pre op radiotherapy)
  • After surgery (post op radiotherapy)

Whether you have radiotherapy before or after surgery depends on the size and type of tumour you have.


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 kills 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 might have 5FU (fluorouracil) or capecitabine chemotherapy at the same time as the radiotherapy. Chemotherapy and radiotherapy given together is called chemoradiotherapy.

If you have a large tumour, you might need a longer course of treatment before surgery. The treatment may last up to 5 weeks. You might 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

This type of radiotherapy means having a radioactive source put next to the tumour inside your rectum. It is also called brachytherapy and there are 2 types.

High dose rate (HDR) internal radiotherapy

This treatment gives radiotherapy directly to the tumour. You might have this if you have a cancer in the middle or lower third of the rectum. You usually have it before surgery. The aim is to shrink the tumour so that it is easier to completely remove it. It can also be used to treat patients who have already had radiotherapy in the past. 

You might 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. They attach the tube 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 doctor takes the tube out. Then you can go home. If you 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. 

Contact radiotherapy

Contact radiotherapy uses low dose X-rays to treat the cancer. It is called Papillon treatment. This type of radiotherapy only goes a few millimetres into the tissue. Your doctor will only offer you this if you have a small, early cancer that is less than 3cm and you can't have surgery because of other medical conditions. You might also be offered it if you don’t want surgery and a stoma.

This treatment is only available in a few hospitals, so you might need to travel quite far to have it.

Before the treatment you have a low fibre diet for 3 days. Immediately before you have treatment you have a small enema to empty your rectum. The doctor then puts some local anaesthetic gel around your anus to numb the area. You also have cream put around the area to relax the muscles.

During the treatment your doctor examines your rectum using a small tube called a sigmoidoscope. They then gently put an applicator into your rectum close to the tumour and put the treatment tube through the applicator. This is attached to a machine. It delivers the radiation to the tumour. Treatment takes about a minute but you will be in the department for about half an hour.

You have the next treatment 2 weeks later. If the tumour has shrunk after the second treatment you have more treatments two weeks apart. The number of treatments you need depends on your cancer. If it is not working you might have external radiotherapy with or without chemotherapy. Or you might need surgery.

Results from studies show there is a slightly higher risk of the cancer coming back after this treatment compared to surgery. About 10 in 100 people (10%) have a recurrence with contact radiotherapy compared with 1 to 4 in 100 people (1 to 4%)  with other treatments. 

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
  • Bowels becoming blocked

Radiotherapy after surgery

If you haven't had radiotherapy before your operation for rectal cancer, your surgeon and cancer specialist might 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 between 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 might have chemotherapy with radiotherapy (chemoradiotherapy).


Planning treatment

Before you begin your treatment, the radiotherapy team carefully plans 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 might take from 15 minutes up to a couple of hours. You have a planning CT scan. The scan shows the cancer and the structures around it.

CT scanner

You lie on the scanner couch with the treatment area exposed. The radiographers 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 might 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 might also make pin point sized tattoo marks in these areas.

After your planning session

You might 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 might be fixed in one position or able to rotate around your body to give treatment from different directions. 

Before your first treatment your radiographers 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 on a closed circuit television screen.

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

Find out about

Side effects of rectal radiotherapy

Latest research into radiotherapy for rectal cancer

Radiotherapy to treat advanced bowel cancer

Chemoradiotherapy for rectal cancer

Bowel cancer tests

Skin markings

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Updated: 11 April 2016