A trial looking at proton beam therapy for breast cancer (PARABLE)

Cancer type:

Breast cancer




Phase 3

This trial is looking at proton beam therapy Open a glossary item for people with breast cancer. It is for people who have an increased risk of developing long term heart problems years after radiotherapy.

More about this trial

After having surgery to remove your cancer, you might have radiotherapy to the breast, chest or armpit. This is to lower the risk of the cancer coming back.

There are short term and long term side effects of radiotherapy for breast cancer. Short term side effects include skin changes and tiredness. Long term side effects include changes to the breast or chest tissues. One long term side effect for a very small number of people is heart problems.

Health care practitioners can estimate who might develop these heart problems. To do this they look at your radiotherapy planning scan together with other factors such as your age and medical history. They then work out your potential lifetime risk. You are able to take part in this trial if your lifetime risk is likely to be increased. It’s important to point out that this possible risk is still very small. 

The standard radiotherapy treatment Open a glossary item for breast cancer uses x-rays. This is the most targeted radiotherapy available for this cancer type.

Proton beam therapy is a type of radiotherapy that uses high energy protons. The radiotherapy team can plan this treatment to a specific depth.

Researchers think proton beam might be better at targeting the breast, chest and armpit, as well as reducing the dose of radiotherapy to your heart. They also want to make sure that there are no more shorter term side effects to the breast and chest, such as skin changes.

In this trial half the people will have standard radiotherapy and the other half will have proton beam therapy. The researchers will compare the 2 groups.

The aims of the trial are to:

  • find out whether proton beam therapy can give a lower dose of treatment to the heart and so lower the risk of long term heart problems
  • check that the risk of other side effects, such as skin and breast changes, is not increased in those who have proton beam therapy
  • compare the short term and longer term side effects of these treatments
  • find out if people are willing to be part of a trial comparing these 2 treatments

Who can enter

The following bullet points are a summary of the entry conditions for this trial. Talk to your doctor or the trial team if you are unsure about any of these. They will be able to advise you. 

Who can take part

You may be able to join this trial if all of the following apply. You:

  • have invasive breast cancer
  • have had surgery to remove the cancer
  • are due to have radiotherapy to the breast, chest or armpit
  • have a predicted increased risk of heart problems due to radiotherapy. Your radiotherapy health care practitioner will talk to you about this.
  • are at least 18 years old

Who can’t take part

You cannot join this trial if any of these apply. You:

  • have cancer that has spread to another part of the body
  • have already had radiotherapy on the same side as this breast cancer was
  • have a medical condition that affects the connective tissue Open a glossary item such as bone, cartilage or muscles. Some people with a connective tissue condition might be able to take part. The trial team can explain more about this if it applies to you.
  • are having trastuzumab emtansine (TDM1) or capecitabine or both with your radiotherapy. You may be able to join the trial if you have these before or after radiotherapy.
  • have a breast tissue expander implant that has metal injection ports

Trial design

This is a phase 3 trial. The trial team need 192 people to take part. 

It is a randomised trial. A computer will put you into 1 of 2 treatment groups. The 2 groups are:

  • radiotherapy – standard treatment
  • proton beam therapy

Everyone has a planning appointment before starting treatment. This appointment includes a scan. This is to work out your dose of radiotherapy and the exact treatment area. 

Both groups have treatment every day Monday to Friday for 3 weeks. 

Standard radiotherapy 
You have treatment at your local radiotherapy centre. 

Proton beam therapy group
You have treatment at either The Christie NHS Foundation Trust in Manchester or the University College Hospital in London. The NHS can arrange accommodation for you and your partner or carer during your treatment. A member of the team will tell you more about this when you join the trial. 

You do not have to stay in the accommodation if, for example, you live close to the NHS proton centre. You might prefer to return home every day following your treatment.

Before proton beam therapy, you have a CT scan Open a glossary item to plan your treatment area.

Samples for research
You can give a blood sample during the trial. Where possible your team take this when you have blood taken as part of your routine care.   

The team ask for a piece of the tissue sample (biopsy Open a glossary item) taken when you were first diagnosed or from your surgery. 

These samples are optional. You don’t have to agree to either of these if you don’t want to. 

Researchers use these samples to find out more about breast cancer.

Quality of life
You fill in questionnaires:

  • before starting treatment
  • once a week during treatment and for 9 weeks after treatment
  • then at 6 months
  • 1 year
  • 2 years
  • 5 years

The questions ask about:

  • your general health and wellbeing
  • what you are able to do
  • side effects
  • using other health services such as your GP 

These are quality of life questionnaires.

Hospital visits

You see the doctor before taking part. This is to: 

  • ask you about your medical history Open a glossary item
  • check your height and weight
  • fill in the first set of questionnaires 

You see a member of the healthcare team once a week during treatment. This is to see how you are and to ask about side effects.

After treatment you see someone at 2 weeks and 3 weeks. If you still have side effects, you continue to see the doctor until you have only 1 side effect or none.

Depending on your hospital these may be face to face or by phone or video.

You then see them at:

  • 3 months
  • 6 months
  • 1 year
  • 2 years
  • then once a year for 3 years

At 2 years you have a CT scan as part of the trial.

Side effects

The trial team monitor you during treatment and afterwards. Contact your advice line or tell your radiotherapy healthcare team if any side effects are bad or not getting better. 
We have information about:



Recruitment start:

Recruitment end:

How to join a clinical trial

Please note: In order to join a trial you will need to discuss it with your doctor, unless otherwise specified.

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Chief Investigator

Professor Charlotte Coles

Supported by

Institute of Cancer Research (ICR)
NIHR Efficacy and Mechanism Evaluation (EME) Programme

If you have questions about the trial please contact our cancer information nurses

Freephone 0808 800 4040

Last review date

CRUK internal database number:


Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Last reviewed:

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