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Side effects of radiotherapy

Radiotherapy to the brain can cause short term side effects such as tiredness and sickness. These side effects usually improve a few weeks after treatment. You may also have long term side effects which can continue for a lot longer and sometimes might be permanent.

Your treatment team will discuss the side effects of radiotherapy with you before you start treatment. They will help you manage any side effects you might have. 

These side effects vary from person to person. They also depend on what other treatment you are having. For example, your side effects could be worse if you are also having chemotherapy.  

You may not have all of the effects mentioned. Side effects can include:

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.

Somnolence syndrome

In a few people, tiredness can become very severe within 5 to 6 weeks after the treatment finishes. This is called somnolence syndrome. You might also have other symptoms such as loss of appetite. 

Somnolence syndrome is more common in children, but can also happen in adults. It doesn't need treatment and gets better on its own over a few weeks.

Radiotherapy to the brain can cause hair loss or thinning. If you are having treatment to a particular part of the head, your hair usually falls out in that area. You might also have some hair loss on the opposite side of the head, where the radiotherapy beams pass through. This area is called the exit site.

Whether or not your hair grows back depends on the type of radiotherapy you're having. For example, if you're having radiotherapy to treat your symptoms, it's likely that your hair will grow back. Whereas treatment to try to cure your cancer uses a high dose of radiation and so permanent hair loss is much more common. 

You might like to cover your head with a soft hat, scarf or wig until your hair grows back. 

You might feel sick during treatment and for a few weeks after the treatment has finished. Sickness is usually well controlled with medicines. Your treatment team can give you anti sickness tablets. Some people find that it helps to take them 20 to 60 minutes before having treatment.

Your doctor might also give you steroids. Radiotherapy to the brain can cause swelling which can lead to nausea. Steroids can help to reduce swelling and sickness.  

Radiotherapy for brain tumours can sometimes make symptoms worse before they get better. This is because the treatment can cause swelling in the brain. The swelling increases the pressure in the head and makes the symptoms worse.

This can be frightening because you might think the radiotherapy isn't working. Increased pressure in the brain might cause:

  • headaches
  • feeling sick
  • fits (seizures)

You usually take steroids during treatment to help with this. 

Side effects of stereotactic radiotherapy and radiosurgery

Stereotactic radiotherapy and radiosurgery target the radiation very precisely at the tumour. This means that the tumour receives a high dose of radiation and the tissues around it receive a much lower dose. So the treatment tends to have fewer or milder side effects, than regular radiotherapy to the brain.

Side effects include: 

  • tiredness
  • feeling sick
  • headaches
  • a patch of hair loss

There is also a small risk of fits (seizures) after radiosurgery. Because of this, the Driver and Vehicle Licensing Authority (DVLA) don't allow you to drive for at least a month after treatment. You must also notify the DVLA. 

Long term side effects

Most side effects gradually go away in the weeks or months after treatment. But some can continue, or start some months or years later.  

Long term side effects won't happen to everyone. It's important to remember that the benefits of the radiotherapy usually far outweigh the risks.

Radiotherapy machines have improved a lot recently. So long term side effects are less common now than they were a few years ago. Side effects can include:

Radiation can cause changes in the brain tissue. Blood vessels may slowly become scarred and blocked, reducing the blood supply to some areas of the brain. This can have an effect on your brain function. Symptoms of this include: 

  • problems thinking clearly
  • difficulty managing tasks that you previously found easy
  • poor memory
  • confusion
  • headaches similar to migraines that come and go (the SMART syndrome)

You might also have symptoms similar to those you had when you were first diagnosed.

Your doctor may suggest that you have an MRI scan or a PET scan to find out whether your symptoms are caused by changes in the brain tissue or by tumour cells. 

Over a period of time, the treated area might develop a small area of dead cells. This is called radiation necrosis.

Radiation necrosis usually happens 1 to 3 years after the treatment finishes. It is more common in people who have had a high dose of radiation to a small area of the brain (radiosurgery). 

Most people don't have symptoms and do not need treatment. A small number of people might develop symptoms that depend on the area of the brain affected. If this is the case, you may have treatment with steroids or an operation to remove the affected area. 

You might have changes in the levels of certain hormones if you have had treatment near your pituitary gland. 

Diagram showing the pineal and pituitary glands

For example, you might have thyroid problems or low levels of steroids. You usually have blood tests to check for this. Your doctor can give you replacement hormones to take if you have changes in the levels of hormones.

In very rare cases, you may develop another brain tumour many years after you were first treated. This is because, although radiation kills cancer cells, it is also a risk factor for developing them. 

Unfortunately, tumours caused by previous radiotherapy tend not to respond very well to treatment. The tumours might be high grade and grow more quickly.

Talk to your treatment team if you are worried about developing a second cancer in the future.

Last reviewed: 
08 Aug 2019
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    VT Devita, TS Lawrence and SA Rosenberg
    Wolters Kluwer Health, 2019

  • Delayed complications of cranial irradiation
    J Dietrich, V Gondi and M Mehta
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  • Stereotactic Radiosurgery and Stereotactic Body Radiation Therapy (SBRT)
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