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 sometimes used to treat people who have:

Chemotherapy may not always be effective at treating cancer cells that 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 radiotherapy in a hospital radiotherapy department. Each treatment session lasts for a few minutes. Your doctor or nurse will tell you how many treatment sessions 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 to help keep your head still. You can breathe through it and it should not be uncomfortable.

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.

Plastic mesh radiotherapy mask 

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. It 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. You may feel tired for several months after treatment has finished.

Some people get somnolence after radiotherapy to the brain. This is extreme tiredness that happens about 4 to 8 weeks after treatment finishes. If you get somnolence, 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. You may get headaches 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. Sickness can usually be treated with anti-sickness drugs (anti-emetics). Your doctor can prescribe these. Tell your doctor if your sickness does not get better. 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

Your healthcare team 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 hairdryer.

You may have a mild skin reaction after PCR. Your skin may become red and itchy and sore behind the ears. It may also become darker. Staff in the radiotherapy department will check your skin for a reaction. 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 1 year afterwards. Cover your head or use suncream with a sun protection factor (SPF) of at least 30.

Effects on memory and thinking

Radiotherapy to the brain may affect your memory and ability to think or reason (cognitive function). After treatment, you may have memory loss or difficulty concentrating.

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

Your feelings about PCR

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 that many people go through when trying to come to terms with their condition.

You may also worry that PCR may affect your memory or ability to think clearly. This is unlikely with the low doses of radiotherapy used for PCR. But it can be useful to discuss any worries you have with your healthcare team.

Getting support

Everyone has their own way of coping with difficult situations. You may find it helpful to talk to family or friends. Or you may prefer to seek help from people outside your 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.

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

About our information

  • References

    Below is a sample of the sources used in our prophylactic cranial radiotherapy information. If you would like more information about the sources we use, please contact us at

    National Institute for Health and Care Excellence (NICE). Lung cancer – Diagnosis and management. Clinical guideline 2019.

    European Society for Medical Oncology (ESMO). Acute lymphoblastic leukaemia in adult patients: ESMO clinical practice guidelines for diagnosis, treatment and follow-up. 2016. European Society for Medical Oncology (ESMO).

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr David Gilligan, Consultant Clinical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 November 2020
Next review: 01 November 2023

This content is currently being reviewed. New information will be coming soon.

Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.