Prophylactic cranial radiotherapy (PCR)

Prophylactic cranial radiotherapy (PCR) is a treatment used to prevent or delay the spread of a cancer to the brain (secondary brain cancer). PCR aims high-energy x-rays at the head and is given by a radiotherapy machine as a series of short, daily treatments. It is usually given to treat small cell lung cancer (SCLC). It may occasionally be given to treat acute lymphoblastic leukaemia (ALL).

Your radiotherapy is carefully planned. As radiotherapy must treat exactly the right area, it’s important to keep that part of the body as still as possible. You’ll be asked to lie back with your head on a firm headrest. A soft clamp may be fitted to your head or a specially made radiotherapy mask may be used to help you to keep still.

Some people have very few side effects from PCR, while others have more. Usually they are mild. They may include:

  • hair loss
  • tiredness
  • drowsiness
  • loss of appetite and taste changes
  • skin changes.

Your doctor, radiotherapy staff or nurse can give you advice and treatment to help you cope with any side effects.

What is prophylactic cranial radiotherapy?

Prophylactic cranial radiotherapy (PCR) is a treatment used to prevent or delay the spread of a cancer to the brain (secondary brain cancer). Prophylactic means preventative and cranial refers to the head.

It is sometimes called PCI, which stands for prophylactic cranial irradiation.

When PCR is given

PCR is usually given to people who have a type of lung cancer called small cell lung cancer (SCLC). It may occasionally be given to people who have acute lymphoblastic leukaemia (ALL). PCR may also help reduce the risk of secondary brain tumours in people who have non-small cell lung cancer (NSCLC), but this is still being researched.

People with SCLC may have PCR when the cancer has not spread to other parts of the body, and has responded well to previous treatments. With SCLC, there is a risk that tiny numbers of cancer cells may spread from the lung to the brain. These would be too small to be seen by scans but in time would grow to form secondary cancers in the brain. Your specialist may recommend PCR to prevent this happening. PCR treats the whole brain.

PCR may be more effective than chemotherapy at treating cancer cells that may have spread to the brain. This is because the brain is protected by a membrane called the 'blood-brain barrier' that stops a lot of chemotherapy drugs from getting to the brain.

PCR may also be useful for people with SCLC who have more advanced disease. Your specialist can advise you whether PCR is an appropriate treatment for you.

Studies show that when PCR is given to people who are in complete remission from SCLC, and who have no signs of the cancer, it can help them to live longer. It reduces the chance of developing a secondary cancer in the brain.

PCR may occasionally be given to people with ALL, if it’s thought that they may be at risk of the leukaemia affecting the brain.

How PCR is given

Radiotherapy treats cancer by using high-energy x-rays that destroy cancer cells while doing as little harm as possible to normal cells. PCR aims these high-energy x-rays at the head and is given by a radiotherapy machine. This is known as external beam radiotherapy. The treatment is given in the hospital radiotherapy department.

Your radiotherapy is carefully planned to make sure that you get the maximum benefit. This may involve a few visits to the radiotherapy department before treatment starts. As radiotherapy is planned very precisely to treat exactly the right area, it’s important to keep that part of the body as still as possible. You’ll be asked to lie back with your head on a firm headrest. A soft clamp may be fitted to each side of your head to hold it steady during treatment.

Alternatively, a see-through perspex device or a plastic mesh may be used to make a mould that fits around your head. The mould is used to help you stay in position during radiotherapy.

PCR is given as a series of short daily treatments (sometimes called fractions) in the radiotherapy department, using equipment similar to a large x-ray machine. Each treatment lasts for only a few minutes. The treatments are usually given from Monday–Friday, with a rest at weekends. The number of sessions will vary depending on your situation.

Side effects of PCR

Each person’s reaction to radiotherapy is different. Some people have very few side effects while others may experience more. Usually the side effects of PCR are mild. If you notice any side effects that you think may be due to PCR but are not listed below, let your doctor, nurses or radiographers know.

Hair loss

Your hair may start to fall out about three weeks after your first treatment. Most hair loss is temporary. Hair usually starts to grow back 2−3 months after you finish treatment. Sometimes it grows back with a slightly different colour and texture, and it may not be as thick as before.


You may find that you feel very tired during treatment. This can often be made worse by having to travel to hospital each day. Listen to your body and allow yourself extra time for a nap during the day. Tiredness may continue for about three months after treatment has finished.


This can occur throughout your radiotherapy and for a time after the treatment has finished. It is usually mild. Drowsiness is at its worst about two weeks after treatment starts, but will then gradually begin to improve. It can sometimes get worse again around 4−6 weeks after treatment finishes, but it will get better a week or so later.


Occasionally, some people experience headaches during treatment. This usually happens in the first few days after starting PCR. It's important to let the staff looking after you know if you have a headache. Your doctor may prescribe painkillers and, sometimes, steroid tablets.

Feeling sick

You may feel sick (nausea), but this is uncommon and can usually be treated with anti-sickness drugs (anti-emetics). Your doctor can prescribe these. If your sickness isn't controlled, or if it continues, tell your doctor. They can prescribe other anti-sickness drugs that may be more effective.

Loss of appetite and taste changes

You may find that food tastes different. If you don’t feel like eating, you can replace meals with nutritious, high-calorie drinks. These are available from most chemists and can also be prescribed by your GP. A dietitian or specialist nurse at your hospital can give you advice.

Skin changes

You may have a skin reaction while having external radiotherapy. With PCR, any skin changes are usually mild, but your skin may become sore behind the ears. People with pale skin may find that the treatment area becomes red, hot, sore or itchy. People with dark skin may find that their skin becomes darker. The degree of any skin reaction depends on the area being treated and your skin type. Staff in the radiotherapy department will be checking for any reaction, but let them know if you notice any changes or feel any soreness.

The staff will also be able to give you advice on skincare. This may vary from one hospital to another and depend on the dose of radiotherapy you are given. They may advise you not to wash the treatment area at all while you are having treatment. Or they may tell you that it's best to use only tepid water and to dry yourself by patting gently with a soft towel and not rubbing.

Because your skin will be sensitive during and after treatment, it's best not to overexpose it to the sun or cold winds. Try wearing soft cotton or silk scarf, or a hat to cover your head when you go outside. It’s also important to cover the treated area if you go out in strong sunshine for at least the first year after radiotherapy.

Your feelings

You may find the idea of radiotherapy to the head worrying. You may have many different emotions, including anger, resentment, guilt, anxiety and fear. These are all normal reactions, and are part of the process many people go through in trying to come to terms with their condition.

People often worry that PCR may affect their memory or their ability to think clearly, but this is very unlikely with the low doses of radiotherapy used for PCR. It can be useful to discuss any worries you have with your doctors or nurses.

Everyone has their own way of coping with difficult situations. Some people find it helpful to talk to family or friends, while others prefer to seek help from people outside their situation. Some people prefer to keep their feelings to themselves. There is no right or wrong way to cope, but help is there if you need it. Our cancer support specialists can give you information about counselling in your area.

Back to External beam radiotherapy explained

Proton beam therapy

Proton beam therapy is a type of external beam radiotherapy. It is only suitable for a small number of people.