External radiotherapy for rectal cancer

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 that 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 and could make you feel nervous when you see them for the first time. The machine might be fixed in one position or able to rotate around your body to give treatment from different directions. The machine doesn't touch you at any point.

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

Photo of a linear accelerator

Before your treatment

Your radiographers will check you have emptied your bowels. They will let you know when to empty your bladder and start drinking water for your bladder prep.

When you are in the treatment room, your radiographers help you get into position on the treatment couch. They line up the radiotherapy machine, using the marks on your skin.

Then they leave you alone in the room for a few minutes for the treatment. This is so they aren't exposed to radiation. 

During the treatment

You need to lie very still. 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

You might have to travel a long way each day for your radiotherapy. This depends on where your nearest cancer centre is. This can make you very tired, especially if you have side effects from the treatment.

You can ask the therapy radiographers Open a glossary item for an appointment time to suit you. They will do their best, but some departments might be very busy. Some radiotherapy departments are open from 7am till 9pm.

Car parking can be difficult at hospitals. Ask the radiotherapy staff if you are able to get free parking or discounted parking. They may be able to give you tips on free places to park nearby.

The radiotherapy staff may be able to arrange transport if you have no other way to get to the hospital. Your radiotherapy doctor would have to agree. This is because it is only for people that would struggle using public transport and have no access to a car. 

Some people are able to claim back a refund for healthcare travel costs. This is based on the type of appointment and whether you claim certain benefits. Ask the radiotherapy staff for more information about this.

Some hospitals have their own drivers and local charities might offer hospital transport. So do ask if any help is available in your area.

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: 
24 Feb 2022
Next review due: 
24 Feb 2025
  • 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

  • Neoadjuvant radiotherapy for rectal cancer management
    G. Feeney and others
    World Journal of Gastroenterology, 2019. Vol 25, (33): pages 4850–4869

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