Radiotherapy for anal cancer
Radiotherapy uses high energy waves like x-rays to kill anal cancer cells. This treats the cancer. But it can also damage nearby healthy cells which can cause side effects to the skin, bowel and bladder. You can also get some general side effects from radiotherapy.
It is important to remember that everyone is different, and side effects can vary from person to person. You may not have all the effects mentioned.
Side effects to radiotherapy can be either short term (acute) or long term (chronic).
Acute side effects tend to start 1 to 2 weeks after you start radiotherapy for anal cancer. They can gradually get worse during treatment. And they may continue to get worse after your treatment ends. Side effects usually begin to improve 2 to 3 weeks after treatment finishes. But they may last 2 to 3 months in total.
Radiotherapy combined with chemotherapy is called chemoradiotherapy. It is the main treatment for anal cancer.
Having both treatments together can make it difficult to tell which side effects are caused by the chemotherapy, and which are caused by the radiotherapy. It can also make the side effects worse.
Read more about chemoradiotherapy
You might open your bowels more often and have loose poos (diarrhoea) after radiotherapy to the anus. This is because radiotherapy can cause swelling and irritation of your anus and rectum (back passage).
Having chemoradiotherapy can make the diarrhoea worse.
Your doctor might prescribe medicines to help reduce the swelling and irritation. This can help reduce the number of times you need to open your bowels.
Drinking plenty of fluids and having a low fibre diet may also help. Your radiographer or radiotherapy nurse can tell you about this. They can give you leaflets about what to eat.
A low fibre diet means:
cutting out whole grain cereals and wholemeal bread
avoiding fibrous vegetables, fruit and fruit juice
The irritation and inflammation usually settles down about 2 to 3 weeks after your treatment ends.
The skin around your anus, genitals and groin can get sore during radiotherapy treatment. This can make it painful, especially when you open your bowels or pee. Your doctor or nurse can prescribe painkillers to help until your skin heals.
Your nurse can tell you how to care for your skin. Keeping the area clean is important. Rubbing while washing can make the soreness worse. Discuss any products you'd like to use first with your specialist, radiotherapy nurse or radiographer.
Wash the skin with lukewarm water and simple soaps - don’t use perfumed or medicated soaps or other products.
Pat the skin dry with a soft towel - or you can use a hairdryer on a cool setting.
Ask your doctor, nurse or radiographer for creams to protect your skin and help it heal quickly.
Try using a soft cushion if you have difficulty sitting comfortably.
Wearing loose, comfortable underwear and clothing can also help.
The soreness should start to improve a few weeks after you finish treatment.
The bladder is close to the anus and rectum. Radiotherapy to the anus often irritates the bladder. And you might get symptoms such as:
feeling like you need to pee often
not being able to pee when you get to the toilet
a burning pain when you pee
needing to pee urgently
Try to drink plenty of fluids.
Avoid drinks that can irritate your bladder - this includes tea, coffee and fizzy drinks.
Some people find that drinking cranberry juice helps their symptoms - speak to your doctor or pharmacist before you try this as it can affect how some medicines such as warfarin work.
Bladder irritation usually settles down after the treatment is over. Let your doctor or nurse know if bladder symptoms continue. You may need to have a tube into your bladder (a urinary catheter) for a short time.
You might also have an infection that needs treatment with antibiotics. This can be difficult to diagnose as some of the symptoms of a urine infection are the same as those caused by radiotherapy. But you might also have:
cloudy pee
blood in your pee
pain in your lower tummy (abdomen) or back
a high temperature - you may also feel hot, cold or shivery
a low temperature
Radiotherapy for anal cancer may cause your pubic hair to fall out. The hair can grow back, but it may be thinner than before treatment.
Radiotherapy can also cause general side effects such as tiredness and weakness and emotional changes.
This video shows people affected by cancer talking about the general side effects of radiotherapy. The video is around 7 and a half minutes long
Last reviewed: 30 Jul 2025
Next review due: 30 Jul 2028
Anal cancer is when abnormal cells in the anus divide in an uncontrolled way. It can start in different parts of the anus and different types of cell.
Radiotherapy is a treatment for cancer. It can be used to try to cure cancer, reduce the chance of cancer coming back or to help relieve symptoms.
Chemotherapy combined with radiotherapy is called chemoradiotherapy. It is the most common treatment for anal cancer that hasn't spread to other parts of your body.
External radiotherapy is normally used to treat anal cancer. You have a planning appointment and a CT scan beforehand and will be told how to prepare for each treatment.
Radiotherapy for anal cancer can cause long term side effects. Some can start months or years after treatment. They are rare but your doctor or specialist nurse can help you manage them.
Anal cancer is cancer that starts in the anus. The anus is also called the anal canal.
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