Radiotherapy
Most side effects gradually go away in the weeks or months after treatment. But some side effects can continue. Or you might notice some that begin months or years later.
Most of these side effects are rare. There are things you can do to deal with any effects that you have.
Tiredness after radiotherapy might carry on for some months. You might also feel weak and lack energy. Various things can help you to reduce tiredness and cope with it, for example exercise.
Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.
Your bowel movements might be looser or more frequent than before your treatment. And sometimes you might pass some blood from your back passage (rectum).
You might need to take anti diarrhoea medicines, such as loperamide (Imodium). Bulking agents, such as Fybogel, might also help. Your doctor or nurse can prescribe these for you. Talk to your doctor before taking these.
It’s usually best to try to have a healthy balanced diet if you can. Try to eat small meals and snacks regularly. Ask with your healthcare team if you need to make any changes to your diet. Some people find it best to avoid high fibre foods such as beans, nuts, seeds, dried fruit, bran and raw vegetables.
Drink plenty to try and replace the fluid lost. Aim for 8 to 10 glasses per day.
Let your doctor know if you have ongoing problems with frequent bowel movements or bleeding. They can refer you to a specialist team. The team includes:
cancer doctors
digestive system specialists
bowel surgeons
dietitians
specialist nurses
Inflammation of the back passage (rectum) is a long term side effect. Proctitis can cause a feeling of wanting to strain whether or not you actually need to pass a bowel movement. You might also have bleeding from your back passage or a slimy mucous discharge.
Bleeding is usually slight but can be more severe for some people. Talk to your radiographer or nurse if you have proctitis. They might suggest you use treatments such as steroid suppositories for a short time. This might reduce the inflammation.
Some people may have changes to the bladder, causing:
leaking of urine (bladder incontinence)
needing to pass urine more often due to the bladder wall becoming less stretchy
fragile blood vessels in the wall of your bladder that might cause blood in your urine
Many people worry about having access to a toilet when they’re out. There are special keys called radar keys. They give you access to thousands of toilets in the UK.
You can also get a 'Just Can't Wait' card, this gives you peace of mind and access to toilets in a rush.
Find out more about these on the Bladder and Bowel Community website
Radiotherapy can damage the bone cells in the pelvic area, and also lower the blood supply to the bones. The bones can become weaker. This is called avascular necrosis. Damage to the bones can cause pain and sometimes makes it hard to walk or climb stairs.
Your doctor will monitor you carefully, including checking your bone strength with a . They might suggest treatment with painkillers and walking aids to help you get around, such as a stick. You might also need to take medicines to strengthen the bones called bisphosphonates. These drugs can help to control pain and reduce the risk of fractures.
Sometimes, tiny cracks can appear in the pelvic bones some years after treatment. They are called pelvic insufficiency fractures. This is more likely to happen in people who have general weakening of their bones as they get older (osteoporosis). It is also more likely in people who are taking hormone therapies or steroids.
The pain, in this case, can be quite bad. It usually gets worse if you move around or do exercise and gets better when you sit still or rest. This type of pain normally goes away overnight. It doesn't stop you from sleeping well. Your doctor might ask you to have x-rays, a CT scan or an MRI scan (or a combination of these) to see if there are any fractures in the bones.
You can have some changes that can affect your sex life. These changes may continue some time after treatment.
Men can experience a lower sex drive, difficulty in getting an erection or problems with ejaculation.
Women may have dryness and shrinkage of the vagina, making sex painful. Some women also experience an early menopause.
Both men and women might lose their fertility.
There are ways of reducing and managing them. Sometimes other conditions can cause similar symptoms to the long term side effects of rectal cancer radiotherapy.
You might have low after radiotherapy to the pelvis (the area between your hip bones). This is called a vitamin B12 deficiency.
Radiotherapy can stop your from taking in (absorbing) vitamin B12 from the food you eat. This is called malabsorption. This means you can have a B12 deficiency even if you eat a balanced diet.
A B12 deficiency can be a cause of . This can lead to weakness, diarrhoea, numbness and tingling.
It’s important that you go to your doctor if you’re experiencing these symptoms so that they can help you.
Last reviewed: 12 May 2025
Next review due: 12 May 2028
Radiotherapy uses high energy waves similar to x-rays to kill bowel cancer cells. It is a treatment for cancer of the back passage (rectal cancer).
Side effects tend to start a week after the radiotherapy begins. They can include feeling tired, sore skin, diarrhoea and passing urine more often.
Coping with cancer can be difficult. You might need emotional, practical and financial support. There is support available from your hospital team.
This section is about treatment for cancer that starts in the back passage (rectal cancer). The main treatments are chemotherapy, surgery, radiotherapy and chemoradiotherapy.
Bowel cancer means cancer that starts in the colon (large bowel) or back passage (rectum). It is also known as colorectal cancer.
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