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Having external radiotherapy treatment

Radiotherapy uses high energy waves similar to x-rays to kill cancer cells.

You might have radiotherapy for cancer of the back passage (rectal cancer). You don't usually have radiotherapy for cancer of the large bowel (colon cancer) unless your cancer has spread. This is called advanced bowel cancer.

External beam radiotherapy directs radiotherapy beams at the cancer from a machine. This is different to internal radiotherapy which means giving radiotherapy to the cancer from inside the body.

This page is about external radiotherapy for rectal cancer that hasn’t spread to another part of the body.

When do you have it?

You might have external radiotherapy:

  • before or after surgery
  • if your rectal cancer has spread (advanced bowel cancer)

You might have radiotherapy at the same time as chemotherapy. This is called chemoradiotherapy.

Before or after surgery

If your doctor thinks you need radiotherapy, you usually have it before surgery. Some people only need a short course of radiotherapy. Doctors call this short course preoperative radiotherapy or SCPRT.

You have daily radiotherapy for 5 days and then have:

  • surgery straight away (within 10 days from starting the radiotherapy)
  • delayed surgery (at least 4 weeks after radiotherapy)

You don't usually have radiotherapy after surgery. But your doctor might suggest this if you were diagnosed with rectal cancer as an emergency and had an emergency operation. Or if your rectal cancer comes back soon after your surgery.

Radiotherapy and chemotherapy together

You might have radiotherapy at the same time as chemotherapy. This is called chemoradiotherapy. Chemotherapy can make the cancer cells more sensitive to radiation.

You are likely to have chemoradiotherapy before your surgery if your doctor thinks you need it. You have radiotherapy every weekday for around 5 weeks. And you have a chemotherapy drug called fluorouracil (5FU) or capecitabine. Doctors call this long course chemoradiotherapy. 

Advanced bowel cancer

You might have radiotherapy if your rectal cancer has spread to another part of your body. This is called advanced bowel cancer. Radiotherapy can shrink the cancer, relieve symptoms and help you feel more comfortable.

Where do you have it?

You have your treatment in the hospital radiotherapy department. You usually have it Monday to Friday. And have a break at the weekend. 

You need to travel to the hospital each time you have treatment. Some hospitals have rooms nearby where you can stay in if you have a long way to travel.

You go to the radiotherapy department from your ward if you are staying in hospital.

The radiotherapy room

Radiotherapy machines are very big. They rotate around you to give you your treatment. The machine doesn't touch you at any point.

Before you start your course of treatment your therapy radiographers Open a glossary item explain what you will see and hear. In some departments the treatment rooms have docks for you to plug in your music player. So you can listen to your own music.

Photo of a linear accelerator

Before each treatment session

The radiographers help you to get onto the treatment couch. You’ll be in the same position as your CT scan.

The radiographers line up the radiotherapy machine using the tattoo marks on your body. Once you are in the right position, they leave the room.

During the treatment

You need to lie very still on your back. Your radiographers might take images (x-rays or scans) before your treatment to make sure that you're in the right position. The machine makes whirring and beeping sounds. You won’t feel anything when you have the treatment.

Your radiographers can see and hear you on a CCTV screen in the next room. They can talk to you over an intercom and might ask you to hold your breath or take shallow breaths at times. You can also talk to them through the intercom or raise your hand if you need to stop or if you're uncomfortable.

You won't be radioactive

This type of radiotherapy won't make you radioactive. It's safe to be around other people, including pregnant women and children.

Travelling to radiotherapy appointments

Tell the radiotherapy department if you prefer treatment at a particular time of day. They can try to arrange this.

Car parking can be difficult at hospitals. It’s worth asking the radiotherapy unit staff:

  • if they can give you a hospital parking permit
  • about discounted parking rates
  • where you can get help with travel fares
  • for tips on free places to park nearby

If you have no other way to get to the hospital, the radiotherapy staff might be able to arrange hospital transport for you. But it might not always be at convenient times. To see if you're eligible they usually work it out based on your earnings or income.

Some hospitals have their own drivers or can arrange ambulances. Some charities offer hospital transport.

Side effects

Radiotherapy for rectal cancer can make you tired. It can also make the skin in the treatment area go red and feel sore.

Last reviewed: 
29 Aug 2018
  • Rectal cancer: ESMO Clinical Practical Guidelines for diagnosis, treatment and follow up
    R Glynne-Jones and others
    Annals of Oncology, 2017. Volume 28, Pages 422-440

  • Association of Coloproctology of Great Britain & Ireland (ACPGBI): Guidelines for the Management of Cancer of the Colon, Rectum and Anus (2017). 
    Colorectal disease Volume 19, issue S1,  Pages 1-97