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Future of Imaging 2020

Image-guided Radiotherapy

Trina Herbert

MR Radiotherapy Operational Superintendent, The Royal Marsden NHS Foundation Trust

Continual advancement of technology in medical imaging directly benefits cancer patients having radiotherapy treatment.

Medical imaging is intrinsic to all aspects of the modern radiotherapy (RT) pathway. A patient’s cancer treatment pathway starts with imaging for diagnosis and staging of their disease. The use of medical imaging continues to be an integral part of their journey into and beyond treatment.

CT scanners

Radiotherapy requires some form of medical imaging, from which a treatment plan can be computed. Imaging information needs to provide both the anatomical and tissue-density information necessary to design a personalised digital plan that will deliver specific doses of radiation to specifically identified anatomy. This includes both the tumour volume and any normal organs that function close to the tumour that might be affected by radiation dose.

Over two decades ago radiotherapy departments began installing dedicated CT scanners for radiotherapy planning, and training their own radiographers to operate them. This is now standard practice, that has been followed by increasing interest in incorporating MR imaging into radiotherapy planning and most recently treatment delivery.

As the use of MRI increased within radiotherapy, so did the need for extra education and training for therapeutic radiographers. Initially, this was met by attending specific external programmes and working with diagnostic radiography colleagues.

Integrating MRI in RT planning

The improved soft-tissue visibility provided by MRI scans is recognised as a benefit by oncologists who provide radiotherapy treatment. It improves treatment planning, particularly in anatomical areas where definition of tissue borders is challenging on CT images alone.

Therapeutic radiographers have begun to collaborate closely with their counterparts in MRI departments to incorporate MRI into the radiotherapy planning pathway. Therapeutic radiographers have involved themselves in the scanning of patients for radiotherapy planning purposes. This has included becoming educated in MRI safety and training in scanner operation.

This integration also informs diagnostic radiographers of particular radiotherapy requirements such as patient preparation, for example, bladder filling, reproducibility of position, immobilisation and optimisation of MRI sequences for accurate treatment planning and calculation.

The manufacturers of MRI scanning systems have recognised the increasing demand for MRI in RT. This has resulted in the development of MR-simulators. Echoing the adoption of CT by radiotherapy departments solely for RT planning, dedicated MR-simulators are now being installed to meet the increasing demand for higher quality soft-tissue imaging. Therapeutic radiographers are expanding their knowledge base in order to effectively operate these systems within radiotherapy departments.

Image-guided radiotherapy

Medical imaging has long been used to verify the accuracy of patient positioning prior to delivering radiotherapy treatments. Plain X-ray films were superseded by electronic portal imaging using megavoltage X-rays that could be registered with digitally reconstructed radiographs to assess and correct displacements in patient positioning.

As imaging techniques developed, so did their use in radiotherapy treatment verification. Modern Linear Accelerators are designed to include cone beam CT scanners that acquire three dimensional images, used by therapeutic radiographers to confirm and adjust patient positioning. They are also used to assess physiological parameters, such as appropriate bladder filling, monitoring weight loss, evaluating tumour response and considering appropriate action to clinical situation, for example lung collapse. Therapeutic radiographers are involved with the interpretation of medical imaging as an intrinsic part of the radiotherapy pathway.

MRI-guided radiotherapy (MRIgRT)

The introduction of MR-Linac technology has expanded the therapeutic radiographers role further. This hybrid technology combines a high-field MR scanner with high-energy X-ray treatment. Therapeutic radiographers are being trained to acquire diagnostic-quality MRI scans for the purposes of re-planning patient’s treatments in a real-time scenario. The technology allows for target organs and organs at risk to be contoured to enable daily adaptation of treatment plans. The superior soft-tissue definition results in reduced inter-observer variability in contouring and may lead to a reduction of treatment margins.

With training, therapeutic radiographers working on this novel technology will be able expand their role by performing this task – a role that has previously been the domain of the oncologist. The incorporation of MRI technology into image-guided radiotherapy is the most recent example of improvements in medical imaging technology being adopted and adapted by the radiotherapy community.

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