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Important step towards MR Linac radiotherapy for lung cancer

MR Linac scanner with Ross Lydall inside

Ross Lydall, Health Editor of the London Evening Standard (pictured above), becoming the first healthy volunteer to be scanned by the MR Linac.

Researchers working with the MR Linac – a pioneering radiotherapy machine – have successfully developed treatment plans for patients with an advanced form of lung cancer.

The plans suggest that treating patients with locally advanced non-small cell lung cancer using the MR Linac system would be at least as effective as using conventional linac radiotherapy.

The study represents a key step towards bringing MR Linac radiotherapy to these patients in the clinic.

How it works

MR Linac systems use magnetic resonance imaging (MRI) to tailor the shape of the radiotherapy beam in real time, and can accurately deliver doses of radiation even to moving tumours.

However, the addition of the magnetic field can affect the way the beam works, so traditional treatment plans – which detail the areas to be targeted by the beam – need to be adapted accordingly.

Using patient MRIs and computer modelling, the researchers found that in every case it was possible to design an MR Linac treatment plan that gave an adequate dose of radiation to the tumour tissue, while avoiding giving too much to the surrounding organs.

The research was supported by Cancer Research UK and NHS funding to the NIHR Biomedical Research Centre at The Institute of Cancer Research, London, and The Royal Marsden NHS Foundation Trust.

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Accurate targeting

Writing in the journal Radiotherapy and Oncology, the researchers from the ICR and The Royal Marsden explained how they prepared the treatment plans.

By analysing MRI scans of 10 patients currently undergoing radiotherapy on conventional linac systems – which deliver pre-planned shapes and volumes of X-rays to areas of the body – the researchers first calculated the volume of the tumours, and included a margin for where the disease may have spread at the microscopic level.

The researchers then added a further margin to allow for patient movement during treatment, simulated for treatment with both linac and MR Linac systems. In standard treatment planning, this margin is usually 7 millimetres.

For the conventional radiotherapy calculation, they used a 7mm plan, but for the MR Linac, they created two plans – one with 7 mm margins and another with estimated 3 mm margins – to allow for the system’s ability to adapt to movement in real time.

For each of the three scenarios, the researchers were able to design a plan to give a high enough dose to the tumour – but using the narrower margin on the MR Linac led to significantly lower doses of radiation affecting the surrounding tissues.

Tailored approach

The research team also designed a second set of treatment plans for an approach called isotoxic intensity modulated radiotherapy (IMRT).

Rather than give every patient a standard dose of radiation, isotoxic IMRT irradiates tumours until one of the surrounding organs reaches an exposure limit. This means that some patients can be given higher doses than they are currently, which can improve their prognosis.

By developing narrow-margin IMRT treatment plans for the MR Linac, the researchers established that it should be possible to target these patients’ tumours with higher doses of radiation than is currently possible, while avoiding more tissue from the surrounding organs.

Study co-leader Professor Uwe Oelfke, Head of the Joint Department of Physics at the ICR and The Royal Marsden, said:

“Current survival rates for patients with locally advanced non-small cell lung cancer are poor, making improvements in disease control essential.

“Our research shows that it is possible to develop treatment plans for these patients using MRI-guided radiotherapy machines, such as our new MR Linac.

“This state-of-the-art technology should enable us to deliver more personalised treatments to patients – increasing the dose to the tumour, while reducing the effect on surrounding tissues.”


radiotherapy Uwe Oelfke lung cancer MR Linac
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