Side effects of radiotherapy

The side effects of radiotherapy for advanced cancer depend on the area that your cancer has spread to. They can include feeling or being sick. 

These side effects usually start a few days after the radiotherapy begins. They might gradually get worse during your treatment or after treatment ends. You usually start to get better 1 to 2 weeks after you finish treatment.

Everyone is different and the side effects will vary from person to person. You might not have all of the side effects we mention.

General side effects

Tiredness and weakness

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.

Reddening or darkening of your skin in the treatment area

Your skin might go red or darker in the treatment area. You might also get slight redness or darkening on the other side of your body. This is where the radiotherapy beams leave the body. 

The red or darker areas can feel sore. Your radiographers will give you creams to soothe your skin. The soreness usually goes away within 2 to 4 weeks of ending the treatment. But your skin might always be slightly darker in that area.

Tell the radiotherapy staff if you notice any skin changes.

Loss of hair in the treatment area

Your hair might fall out in the treatment area, but this does not always happen. Whether you have hair loss depends on:

  • the dose of radiotherapy
  • where on your body you have the radiotherapy

Hair usually grows back for most people. Ask your doctor whether your treatment is likely to cause hair loss.

Radiotherapy to the stomach area

You might have radiotherapy over a few weeks to shrink your tumour.

Radiotherapy to control bleeding from your stomach may can be a shorter treatment. How many treatments you need varies. The side effects are usually less severe if the treatment is for a few days and more if your treatment is for a few weeks.

Feeling or being sick

Radiothearpy to the stomach area can make you feel sick or be sick. This can start a few hours after treatment and last for a few days. Anti sickness injections and tablets can control it. Tell your doctor or nurse if you feel sick. You might need to try different anti sickness medicines to find one that works.

Contact your doctor or nurse straight away if you’ve been sick more than once in a day.


  • Avoid eating or preparing food when you feel sick.
  • Avoid foods that are fried, fatty, or have a strong smell.
  • Drink plenty of liquid to stop you from getting dehydrated.
  • Relaxation techniques help control sickness for some people.
  • Ginger can help – try it as crystallised stem ginger, ginger tea or ginger ale.
  • Fizzy drinks help some people when they’re feeling sick.


Radiotherapy to the stomach area might cause diarrhoea. Your poo (stool) may be very watery and have a strong smell. And you might need to poo more often or need to go the toilet more urgently.

Drink at least 2.5 litres of fluid a day to help keep you hydrated. Let your doctor or nurse know straight away if the diarrhoea is severe or getting worse.

Ask your nurse about soothing creams to apply around your back passage (anus). The skin in that area can get very sore.

Loss of appetite

Radiotherapy to your stomach can damage the cells of the stomach lining for a short time. This makes eating more difficult. Ask to see a dietitian if you have problems with eating and drinking.

Tips for eating and drinking

  • Drink about 3 litres of water a day while having treatment. Eating soft foods can be easier.
  • Make sure that you eat slowly and avoid eating late in the day.
  • Eat small amounts often, rather than big meals.
  • Try different foods. You can have high calorie drinks to boost your calorie intake if you need them.

You might need to have liquid food into your vein or through a tube into your nose or stomach if you can’t eat enough.

Side effects of chemotherapy with radiotherapy

Chemotherapy combined with radiotherapy can make some side effects worse. Combining these treatments is called chemoradiotherapy.

Radiotherapy to other areas of the body

You might have radiotherapy to treat cancer that has spread elsewhere in the body. So your side effects will depend on the part of the body you have treatment to.

For example, some people have radiotherapy to treat cancer that has spread to their lungs. The aim of radiotherapy is usually to control cancer growth and relieve symptoms. But it might cause breathlessness at first.

Last reviewed: 
29 Aug 2019
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