Radiotherapy for anal cancer

Radiotherapy is the use of high-energy rays to treat cancer. It can be given on its own or with chemotherapy to treat anal cancer.

Anal cancer radiotherapy

Radiotherapy uses high-energy rays to treat cancer. It destroys cancer cells in the area where treatment is given, while doing as little harm as possible to normal cells.

Anal cancer is usually treated with radiotherapy, in combination with chemotherapy (chemoradiation). You can also have radiotherapy on its own if your doctors think you are not well enough to have chemoradiation.

Radiotherapy may also be used to relieve symptoms if the cancer has spread to other parts of the body.

Getting support

We understand that having treatment can be a difficult time for people. We're here to support you. If you want to talk, you can:

External beam radiotherapy

External beam radiotherapy is given from a radiotherapy machine outside the body.

This treatment is normally given as a number of short, daily treatments in a radiotherapy department. These are called treatment sessions or fractions. It is given using a machine that looks like a large x-ray machine or CT scanner.

Each treatment takes 10 to 15 minutes. The treatments are usually given Monday to Friday, with a rest at the weekend. Your doctor will talk with you about the treatment and possible side effects.

Intensity-modulated radiotherapy (IMRT)

A type of radiotherapy called IMRT is usually used for anal cancer.

IMRT shapes the radiotherapy beams. This allows different doses of radiotherapy to be given to different areas. It means that lower doses can be given to healthy tissue – especially tissue that’s more easily damaged by radiotherapy. This lowers the chance of immediate and long-term side effects. For example, it can reduce the risk of long-term bowel problems.

Your doctor can tell you more about IMRT and whether it’s a suitable treatment for you.

Conformal radiotherapy

Conformal radiotherapy is another way of giving radiotherapy.

The radiotherapy beams are specially shaped to fit the treatment area. This can reduce the side effects of the radiotherapy

Planning your radiotherapy treatment

You will have a hospital appointment to plan your treatment. You will usually have a CT scan of the area to be treated. During the scan, you need to lie in the position that you will be in for your radiotherapy treatment.

Your radiotherapy team use information from this scan to plan:

  • the dose of radiotherapy
  • the area to be treated.

You may have some small, permanent markings made on your skin. The marks are about the size of a pinpoint. They help the radiographer make sure you are in the correct position for each session of radiotherapy.

These marks will only be made with your permission. If you are worried about them, talk to your radiographer.

The doctor may place a small metal marker on the skin around your anus. The marker shows up on the scan so the doctor can see the exact area to be treated.

Treatment sessions

The radiographer will explain what will happen. At the start of each treatment session (called a fraction), they make sure you are in the correct position on the couch and that you are comfortable.

When everything is ready, they leave the room so you can have the radiotherapy. The treatment only takes a few minutes. You can talk to the radiographers through an intercom or signal to them during the treatment. They can see and hear you from the next room.

During treatment, the radiotherapy machine may automatically stop and move into a new position. This is so the radiotherapy can be given from different directions.

Side effects of radiotherapy

You may have side effects during your treatment. Side effects build up slowly when you start treatment. They usually get better slowly over a few weeks or months after treatment finishes.

Your doctor, nurse or radiographer will discuss this with you so you know what to expect. Tell them about any side effects you have during or after treatment. There are often things they can do to help.

We have more information about managing side effects of pelvic radiotherapy.

Side effects caused by smoking

The side effects of radiotherapy are made worse by smoking. Smoking will also make your treatment less effective. Your cancer doctor or nurse will advise you to try to stop smoking. They can give you support and advice.

NHS Smokefree can offer advice and support. You can find out more by visiting


Tiredness (fatigue) can continue for weeks or a few months after your treatment has finished. You might be more tired if you have to travel to hospital each day. If you are also having other treatment such as chemotherapy, this can make you even more tired.

Try to get as much rest as you can, especially if you have to travel a long way for treatment. Balance this with some physical activity, such as short walks, which will give you more energy.

Diarrhoea and passing wind

Radiotherapy is likely to cause changes in how your bowel works. This can cause problems such as diarrhoea or passing more wind than usual. Your doctor can prescribe medicines to help.

Your nurse, radiographer or a hospital dietitian may give you advice about avoiding certain foods. We have more information about coping with problems such as diarrhoea and wind.


You may have some stinging or pain when you pass stools (poo). Your doctor can prescribe local anaesthetic creams to help with this. Tell your doctor or nurse if you have any pain.

Skin reaction

It is likely that your skin will be sore in the area being treated.

This usually happens 2 to 3 weeks after treatment starts. You may have soreness around the anus and in the groin. Men may have soreness in the scrotum. Women may have soreness in the vulva. If you have IMRT, your doctor may be able to avoid these areas. This means that skin reactions are usually milder.

The radiographer or nurse will check the area and tell you how to look after your skin. It is important to follow the advice they give you and only use products they recommend.

Sometimes the skin may become blistered and sore, which can be painful. Your doctor can prescribe painkillers, creams and dressings to help with this. The skin reaction may get worse towards the end of treatment and for up to 6 weeks afterwards. It usually heals quickly after that.

If your skin reaction makes passing urine (pee) painful, your doctor may suggest you have a fine tube (catheter) put into your bladder to drain the urine. They will remove this when your skin has healed.

Inflammation of the bladder (cystitis)

Radiotherapy to the anal area may cause inflammation of the lining of the bladder. This can make you feel you want to pass urine more often. It also gives you a burning feeling when you pass urine.

It helps to drink plenty of water and other fluids. Your doctor can prescribe medicine to make passing urine more comfortable.

Feeling sick

Radiotherapy may make you feel sick (nausea) or be sick (vomit). Sickness can usually be well controlled and stops when treatment finishes. Your healthcare team may give you anti-sickness (anti-emetic) drugs to prevent nausea or vomiting.

Hair loss

Most people lose their pubic hair. It should grow back after your treatment finishes, although the hair loss may be permanent.

Possible late effects of radiotherapy

You may still have side effects months after treatment finishes. Or you may develop new side effects months or years later. These are called long-term side effects or late effects. Newer ways of giving radiotherapy aim to reduce the risk of getting late effects.

There is slightly more risk of developing late effects when you have radiotherapy and chemotherapy together (chemoradiation). Your doctor or nurse will talk to you about this.

We have more information about the late effects of pelvic radiotherapy.

About our information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Chief Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Date reviewed

Reviewed: 30 April 2020
Next review: 30 April 2023

This content is currently being reviewed. New information will be coming soon.

Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

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