Chemoradiotherapy for rectal cancer

Treatment with chemotherapy and radiotherapy together is called chemoradiotherapy. You might have this treatment for cancer of the back passage (rectal cancer). 

Radiotherapy uses radiation, usually x-rays, to destroy cancer cells. It is targeted at the pelvis only and treats the cancer and nearby tissues. 

Chemotherapy uses anti cancer (cytotoxic) drugs to destroy cancer cells. The drugs circulate throughout the body in the bloodstream. Chemotherapy makes the body more sensitive to the effects of radiotherapy. 

Giving these treatments together before surgery can reduce the size of the rectal cancer and lower the chance of your cancer coming back.

When do you have chemoradiotherapy?

You usually have chemoradiotherapy before surgery. Doctors also call this long course chemoradiotherapy. Long course means the treatment is given daily over 5 to 5 ½ weeks. 

You might have chemoradiotherapy before surgery if:

  • your rectal cancer has spread to nearby structures and tissues
  • it might be difficult for your surgeon to remove the rectal cancer with a clear border of tissue (margin)

Before your treatment


You have blood tests before and during your treatment. They check how well your liver and kidneys are working and that it is safe to give the treatment.

DPD deficiency 

Between 2 and 8 out of 100 people (2 to 8%) have low levels of an enzyme called dihydropyrimidine dehydrogenase (DPD) in their bodies. A lack of DPD can mean you’re more likely to have severe side effects from the chemotherapy drugs capecitabine or 5-fluorouracil (5FU). These side effects can rarely be life threatening.

Before starting chemoradiotherapy treatment you have a blood test to check levels of DPD. If the test confirms you have this enzyme deficiency, the chemotherapy amount (dose) will be reduced or removed from your treatment. Your doctor or nurse will talk to you about this.

Pregnancy, contraception and fertility

Tell the team looking after you if you think you might be pregnant before treatment starts. Both men and women should use contraception during chemoradiotherapy. This is because these treatments can damage sperm and eggs or harm a developing baby. 

Chemoradiotherapy to the pelvis can cause infertility. If infertility is an issue for you or your partner, talk to the team looking after you. They can refer you to a fertility specialist before starting treatment.

We have more information about radiotherapy and fertility.

We also have information about chemotherapy and fertility and ways to preserve fertility. 

How do you have chemoradiotherapy?


You have treatment in the hospital radiotherapy department as an outpatient.

Before you begin treatment, the radiotherapy team will decide how much radiation you need. They divide it into a number of smaller treatments. They call each treatment a fraction.

Before starting your treatment, you will attend a planning appointment. You will have a CT scan and the radiographers will make pen marks or small tattoos on your skin. These marks or tattoos are used during your treatment to ensure the radiotherapy is accurately targeted at the cancer.

Your treatment starts a few days or up to 3 weeks after the planning session. You have radiotherapy from an external machine called a linear accelerator.

It is a daily treatment, five days a week for around 5 weeks.


The most common chemotherapy is a tablet called capecitabine (Xeloda). Another treatment is the chemotherapy drug 5 fluorouracil (5FU) given into a vein (intravenously). But this is less common. 

Capecitabine (Xeloda) is a tablet taken twice a day. You start taking capecitabine on the 1st day of your radiotherapy and stop taking it on the last day of radiotherapy. 

You must take tablets according to the instructions your doctor or pharmacist gives you. Whether you have a full or empty stomach can affect how much of a drug gets into your bloodstream.

You should take the right dose, not more or less. Never stop taking a cancer drug without talking to your specialist first.

You can read more about the different chemotherapy drugs and how they are given on our A to Z cancer drugs list.

Side effects of the radiotherapy

Everyone is different and the side effects vary from person to person. This treatment may cause more severe side effects than having radiotherapy or chemotherapy on its own. 

The team looking after you will check your wellbeing. They can make adjustments to your treatment or medication if needed. 

Radiotherapy side effects can be early or late side effects. Early side effects happen in the few weeks following treatment. Late side effects happen many months or years after treatment has finished.

Your specialist team will discuss these with you before starting treatment.

Early side effects

The early side effects gradually develop and can get worse during the treatment. They may continue to get worse after your treatment ends but most of the effects begin to improve after 1 or 2 weeks.

Some common side effects of chemoradiotherapy for rectal cancer include:

  • inflammation of your bowel causing diarrhoea

  • inflammation of your bladder causing stinging and burning (cystitis) when you pass urine

  • tiredness and weakness

  • feeling or being sick

  • itchy, dry, red or sore skin around the back passage (anus)

Late side effects

These may happen many weeks, months or years after treatment finishes. Not everyone will have these side effects.

There are things you can do to deal with any late side effects that you have. Speak to your specialist if they are a problem for you.

  • bowel changes such as needing to go for a poo more often or more urgently

  • bladder changes such as needing to pee more often

  • bone pain in your pelvis

  • fertility problems and changes to your sex life

  • a small risk of a second cancer developing in the pelvis many years later. Speak to your specialist if you are worried

Side effects of the chemotherapy

These side effects can occur during the period you are receiving chemotherapy. They usually get better within a few days of completing the treatment.

  • an increased risk of infection

  • bleeding and bruising easily

  • a drop in the number of red blood cells making you pale and breathless (anaemia)

  • feeling very tired and weak

  • feeling or being sick

  • chest pain or a stroke - this is rare but go straight to A and E if you have these symptoms

  • a sore mouth or mouth ulcers

  • sore, red, peeling skin on the palms of your hands or soles of feet

  • 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                                                                                                                                                                     

  • Colorectal cancer 
    The National Institute for Health and Care Excellence (NICE), 2020. Updated December 2021

  • Colorectal cancer
    British Medical Journal (BMJ) Best Practice Online (Accessed February 2022)


Last reviewed: 
21 Feb 2022
Next review due: 
21 Feb 2025

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