Radiotherapy
Side effects tend to start a week after the radiotherapy begins. They gradually get worse during the treatment and for a couple of weeks after the treatment ends. But they usually begin to improve after around 2 weeks.
The side effects vary from person to person. You might not have all of the following side effects.
You might feel tired during your treatment. It tends to get worse as the treatment goes on. You might also feel weak and lack energy. Rest when you need to.
Tiredness can carry on for some weeks after the treatment has ended. But it usually improves gradually.
Various things can help you to reduce tiredness and cope with it, such as exercise. Some research has shown that taking gentle exercise can give you more energy. It's important to balance exercise with resting.
The skin around your anus and back passage (rectum) is very sensitive. Radiotherapy can make it red and sore.
Wash your skin with tepid water and simple soaps.
Pat your skin dry with a soft towel.
Ask your doctor, nurse or radiographer for creams to protect your skin and help it heal quickly.
Don't use perfumed or medicated soaps and lotions.
Try using a soft cushion if you have difficulty sitting comfortably for a while.
After your treatment is over, the soreness should gradually get better over a few weeks.
Tell your doctor, nurse or radiographer if you have diarrhoea. They can prescribe medicine to help you.
Drink plenty of fluids. This helps to keep you hydrated.
Ask your nurse about soothing creams to apply around your back passage (rectum). The skin in that area can get very sore and even break if you have severe diarrhoea.
For a while after having the treatment you might feel that you have to pass urine more often than usual. And you may have a burning feeling when you do. Or you might feel that you can’t wait then you need to go. This is called cystitis.
The treatment temporarily inflames the lining of your bladder. It helps to drink plenty of fluids. You might find that some drinks increase the soreness, such as tea and coffee. You can experiment for yourself and see what works for you.
Tell your doctor or nurse if you have bladder soreness. They can prescribe medicines to help.
You can get a card to show to staff in shops or pubs. It allows you to use their toilets without them asking awkward questions. You can get the cards from Disability Rights UK or the Bladder and Bowel Community. They also have a map of all the public toilets in the UK.
Disability Rights UK can also give you a key for disabled access toilets so that you don't have to ask for a key when you are out.
This video shows a woman affected by cancer talking about the possible side effects of radiotherapy to the or . This treatment is for a number of cancer types. So not all the side effects might be relevant for you.
The video is around 5 and a half minutes long.
This video shows a man affected by cancer talking about the possible side effects of radiotherapy to the pelvis or abdomen. This treatment is for a number of cancer types. So not all the side effects might be relevant for you.
The video is around 5 and a half minutes long.
Most side effects gradually go away in the weeks or months after treatment. But some side effects can continue or might start some months or years later.
Long term side effects of radiotherapy
Chemotherapy combined with radiotherapy can make some side effects worse. Combining these treatments is called chemoradiotherapy.
Last reviewed: 25 Apr 2025
Next review due: 25 Apr 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).
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.
This section is about treatment for cancer that starts in the back passage (rectal cancer). The main treatments are chemotherapy, surgery, radiotherapy and chemoradiotherapy.
Living with bowel (colorectal) cancer may mean you have changes to your diet, sex life or body image. There is support to help you cope.
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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