Prophylactic cranial radiotherapy (PCR)

Prophylactic cranial radiotherapy (PCR) is treatment to prevent or reduce the risk of cancer cells spreading to the brain.

What is prophylactic cranial radiotherapy (PCR)?

PCR is also sometimes called prophylactic cranial irradiation (PCI).

It is used to prevent or reduce the risk of cancer cells spreading to the brain. Prophylactic means preventive, and cranial means the head.

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 sometimes be given to people who have acute lymphoblastic leukaemia (ALL) and lymphoblastic lymphoma, if their doctor thinks there is a risk of the leukaemia affecting the brain.

PCR may help reduce the risk of secondary brain tumours in people who have non-small cell lung cancer (NSCLC), but research suggests there is no overall benefit, so it is not usually given.

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 over time, they would grow into secondary cancers in the brain. Your specialist may recommend PCR to stop this happening. It can help people with SCLC live longer.

If chemotherapy has worked well, people with SCLC may have PCR in these situations:

PCR treats the whole brain. It is given because chemotherapy is not good 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. This stops a lot of chemotherapy drugs from getting to the brain.

How PCR is given

Radiotherapy uses high-energy x-rays to destroy cancer cells, while doing as little harm as possible to normal cells.

You have the treatment in the hospital radiotherapy department. Each treatment lasts for a few minutes. You usually have treatment every day from Monday to Friday, with a rest at weekends. Your doctor or nurse will tell you how many treatments you will have.

Your radiotherapy is carefully planned to make sure it works as well as possible. You may have a mask made from a plastic mesh. You wear this during your treatment. It helps keep your head still so the treatment is effective. You can breathe through it and it should not be uncomfortable.

Plastic mesh radiotherapy mask 

At the beginning of each session of radiotherapy, the radiographer positions you carefully on the couch and makes sure you are comfortable.

You are alone in the room during treatment. But you can talk to the radiographer, who is watching from the next room.

Possible side effects of PCR

Each person’s reaction to radiotherapy is different. Some people have very few side effects, and other people have more. Usually the side effects of PCR are mild.

Hair loss

You will lose your hair when you have PCR, but this is usually temporary. Your hair may start to fall out about 3 weeks after your first treatment. Hair usually starts to grow back 2 to 3 months after you finish treatment. Sometimes it grows back a slightly different colour and texture than it was before, and it may not be as thick.


Radiotherapy can make you tired, especially if you have to travel a long way for treatment each day. Tiredness can continue for several months after treatment has finished.

Somnolence is an extreme tiredness some people get after radiotherapy to the brain. It happens about 4 to 8 weeks after treatment finishes. You may:

  • have very little energy
  • feel sleepy
  • spend a lot of time sleeping.

This slowly gets better over a few weeks.


Some people have headaches during treatment. This can happen in the first few days after starting PCR. It is important to tell the staff looking after you if you have a headache. Your doctor may prescribe painkillers, or sometimes steroids.

Feeling sick

You may feel sick (nauseous), but this is not common. It can usually be treated with anti-sickness drugs (anti-emetics). Your doctor can prescribe these. Tell your doctor if your sickness:

  • is not controlled
  • continues.

They can prescribe other anti-sickness drugs that may be more effective, or steroids.

Loss of appetite and taste changes

You may find that food tastes different. If you do not want to eat, you can replace meals with nutritious, high-calorie drinks. These are available from most chemists. Your GP can also prescribe them. A dietitian or specialist nurse at your hospital can give you advice.

Skin changes

The hospital staff will advise you on how to look after your skin. Do not put anything on the treated area of your skin before checking with your nurse or radiographer.

Wash your hair or scalp gently with lukewarm or cool water. Gently pat your hair or scalp dry with a soft towel. Do not rub it, and do not use a hair-dryer.

You may have a mild skin reaction after PCR. Your skin may become red and itchy and sore behind the ears. After treatment, your skin may become darker. Staff in the radiotherapy department will check you for a reaction but tell them if you notice any changes or feel any soreness.

If you have a skin reaction, wear a scarf or hat to protect your head from the sun or cold until it gets better. Avoid exposing your head to the sun during treatment and for at least a year afterwards. Cover your head or use sun-cream with a sun protection factor (SPF) of at least 30.

Effects on memory and thinking

Radiotherapy to the brain may affect a person’s memory and their ability to think or reason (cognitive function). After treatment, they may have short-term memory loss or difficulty concentrating.

Your doctors can explain more about this. They will think about the risk of this happening compared to the benefit of PCR. The effects on memory are more likely to happen in older people who have PCR.

Getting support

Macmillan is here to support you. If you would like to talk, you can do the following: