Side effects of radiotherapy

Side effects tend to start a few days after you start radiotherapy. They gradually get worse over the days and weeks of your treatment. They can continue to get worse after your treatment ends. But they usually start to get better after 2 or 3 weeks.

Getting over a long course of treatment completely can take quite a few months. If you had chemotherapy at the same time as radiotherapy, it can take a few months for the side effects to settle. 

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.

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. This may start after your radiotherapy treatment is completed. Your radiographers may 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.

Your throat might get sore. It may be painful to swallow drinks or food.

You can have painkillers to reduce the soreness and you may need strong painkillers, such as morphine as you go through the treatment. Take them half an hour before meals to make eating easier.

Tell your doctor or nurse if your throat is sore.

During and after treatment, you might have a feeling of a lump in the throat when you swallow. This can make it difficult to swallow solid foods.

This problem is often at its worst about 10 days to 2 weeks after you finish treatment.

Speech and language therapists play an important role during your treatment. They will help you with swallowing difficulties (dysphagia) and help you eat and drink safely. They can give information to your family or carer on how to support you with swallowing difficulties. A dietitian can also give advice on what to eat when you have swallowing problems.
Tips for eating and drinking
  • Drink about 3 litres of water a day while having treatment.
  • Eat soft foods.
  • Eat slowly and avoid eating late in the day.
  • Drink plenty during and after meals to soften your food.
  • Eat small amounts often rather than big meals.
  • Try different foods to find out which are easiest to swallow.
  • You can have high calorie drinks to boost your calorie intake if you need them.

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

Your mouth might get very dry, which can be uncomfortable. Various things can help.


  • Try to drink at least 3 pints (one and a half litres) of fluid a day.
  • Choose meals that are moist.
  • Use gravies and sauces to make swallowing easier.
  • Take regular sips of water with your meal to help you chew and swallow your food.
  • Suck small amounts of ice chips to refresh your mouth.
  • Chew sugar free chewing gum.
  • Try eating fresh pineapple.
  • Get your doctor or nurse to give you medicines to stimulate your salivary glands.
  • Ask your doctor about artificial saliva products, such as tablets, mouthwashes, gum, pastilles, and toothpaste.
  • It is very important to have regular check ups with your dentist.

Your voice might become hoarse as you go through your radiotherapy. Depending on the area being treated your voice may disappear altogether. It will come back, but may sound different afterwards. 

After radiotherapy to treat a head and neck cancer, you are at risk of getting swelling called lymphoedema in your neck or face. Lymphoedema is pronounced lim-fo-dee-ma.

Lymph fluid is in all body tissues. It comes from the tiny blood vessels into the body tissues. Usually, it drains back into the bloodstream through channels called lymph vessels. These are part of the lymphatic system.

A build up of lymph fluid in an area of the body can happen if lymph drainage channels or lymph nodes are blocked, removed, or damaged.

Lymphoedema in the head or neck can also cause symptoms inside your mouth and throat. For example, swelling of your tongue and other parts of your mouth.

Tell your doctor or nurse straight away if you:

  • have any swelling in the head or neck area or a feeling of fullness or pressure
  • find it difficult to swallow
  • have changes in your voice

Lymphoedema is easier to control if treated early. It's important that you are referred to a lymphoedema specialist if you have signs of swelling. This is usually a nurse or physiotherapist.

Radiotherapy to the larynx might affect the thyroid gland. It may become underactive. This can happen many years after treatment.

If you are at risk of an underactive thyroid your GP will do regular tests to check your thyroid hormones.

Many people feel low in mood during or after radiotherapy treatment for the larynx. If you feel like this, make sure you get support early. Speak to your specialist nurse, members of your healthcare team or GP.

Side effects if you have chemotherapy with radiotherapy

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

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    National Cancer Action Team, August 2012

  • Radiotherapy Services in England 2012

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    S Ahmed and others. British Medical Journal, 2012. Vol. 345

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    B Smith and others
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  • Glottic Cancer

    A Williamson and S Bondje

    StatPearls Publishing; 2021 January

  • Evaluation of Thyroid Cancer Risk After Laryngeal and Nasopharyngeal Radiotherapy

    H Ghaznavi

    Reports of Radiotherapy and Oncology, 2020; 7(1) :e111991

Last reviewed: 
06 Dec 2021
Next review due: 
06 Dec 2024

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