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First UK proton beam therapy trial for breast cancer launches

Published: 03 January 2023

A new trial is testing the benefits of proton beam therapy for certain patients with breast cancer for the first time in the UK.

The PARABLE trial is funded by a Medical Research Council (MRC) and NIHR partnership. It is being led by researchers at The University of Cambridge, The Institute of Cancer Research (ICR) and The Royal Marsden NHS Foundation Trust. Researchers will compare proton beam therapy with standard radiotherapy for patients who are at greater risk of long-term heart problems after radiotherapy treatment.

The trial will help find out whether proton beam therapy can help to deliver adequate doses of radiotherapy to breast tissue, while minimising off-target radiation delivered to the heart.

Every year in the UK over 30,000 people with breast cancer receive radiotherapy following surgery as part of their treatment. Standard breast cancer radiotherapy uses high energy x-rays to kill cancer cells. As well as lowering the risk of cancer coming back, radiotherapy can increase survival rates.

Standard breast cancer radiotherapy is very effective for the vast majority of people and the benefits far outweigh small side effects. Yet, there can be a very small risk of radiotherapy leading to heart problems much later in life (less than 1% of people treated).

The risk of heart problems later in life due to breast radiotherapy may be higher than 1% for a very small group of people. This is usually because their breast tissue and the lymph nodes, which need radiotherapy treatment, are close to the heart, and/or because they have an increased underlying risk of developing heart problems later in life.

Proton beam therapy uses charged particles instead of x-rays to target tumours more precisely. Researchers hope it will allow doctors to deliver the required dose of radiotherapy where it is needed. Alongside minimising the dose of radiation delivered to the heart. Without increasing the risk of early side effects such as skin redness and changes in breast appearance.

The average radiotherapy dose that the heart is likely to receive from the radiotherapy planning scan is estimated together with age and other medical history. This information is used to predict the potential small lifetime risk of heart problems.

People predicted to have at least a 2% or more potential lifetime risk of heart problems from radiotherapy will be invited to take part.

Around 500 out of every 30,000 people who receive radiotherapy for breast cancer fall into this category. People who enter the trial will either receive standard radiotherapy or proton beam therapy.

The trial will enrol 192 people across 22 UK sites managed by The Institute of Cancer Research.

The trial will measure radiation dose delivered to the heart as an early predictor of possible heart problems. This is to avoid unnecessary lengthy follow up for many years before results are available.

Participants will record their experiences using questionnaires so that researchers can assess side-effects including skin reactions, breast pain and swelling, and other symptoms.

Proton beam therapy has been trialled in other countries to treat breast cancer, but numbers of participants in these trials are small. There are no reported trials that directly compare proton beam therapy with standard radiotherapy.

Researchers stress the importance of evaluating the benefits of proton beam therapy – which is expensive and only available in certain locations across the UK – thoroughly in a clinical trial.

Professor Jonathan Wadsley, National Specialty Lead for Radiotherapy and Imaging at the NIHR, which funded the trial, said: "The UK is currently leading the way in developing the evidence base to demonstrate when proton beam radiotherapy can provide significant clinical benefit to some patients over conventional radiotherapy.

"It is exciting to see the launch of the first trial aiming to demonstrate the benefit of this treatment for a subset of patients with breast cancer."


More information about the study can found on the NIHR Funding & Awards Website.

The trial was funded by the NIHR Efficacy and Mechanism Evaluation Programme.

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