Development of MRI-guided radiation therapy

Lead Research Organisation: Institute of Cancer Research

Abstract

Radiation therapy involves delivering high-energy X-ray beams to tumours in order to kill cancer cells. For many people with cancer, radiation therapy is very effective and frequently cures their disease. Unfortunately, when treating tumours, nearby normal tissues will inevitably receive some of the radiation and this is associated with side effects. These side
effects can vary from mild, temporary changes that disappear completely to severe, life-threatening, permanent effects that chronically affect a patient's quality of life. Therefore, when treating patients with radiotherapy, there is a clear need to
ensure that the treatment is delivered as accurately as possible in order to avoid unnecessary treatment of normal tissues.
In most cases, radiotherapy is planned using a CT scan to show the position of the tumour, but this is usually only done once before the treatment starts.
One of the major problems with accurate delivery of radiation lies in the fact that it can be very difficult to determine precisely where the tumour is, because it can be difficult to see on standard CT scans. The problem is compounded by the fact that radiation therapy is usually given as a series of doses (called fractions) divided over a period of weeks and the tumour may be in a slightly different position each day or may shrink during the course of treatment. To make matters even
more difficult, tumours often occur in tissues that move. For example, lung tumours can move quite significantly as a patient breathes in and out. Therefore, when planning a course of radiation therapy, it is necessary to include a large
margin around the tumour to make sure that the radiation beams do not miss their target. As a result, large volumes of normal tissues may receive unnecessarily high radiation doses.
In this research project, we aim to revolutionise the technique for delivering radiation therapy by developing a new type of machine called an MR Linac (or magnetic resonance imaging-guided linear accelerator). This machine combines a state-of-the-art radiation machine (called a linear accelerator) with a magnetic resonance imaging (MRI) scanner. MRI scanning is better than CT scanning at being able to tell the difference between tumour and normal tissues and does not expose patients to additional radiation doses. Therefore, such a machine will allow us to see very accurately where the tumour is at the time of each fraction of radiation therapy and it will also be able to track the movements of a tumour as they occur in real-time within a patient during a dose of radiation. With these improvements, we aim to be able to reduce the margins we place around tumours before we start a course of radiation therapy and yet still be confident that we are hitting the tumour target all of the time. For patients, this will have a number of benefits including greater confidence that the treatment will be effective against their disease with fewer side effects. The greater level of accuracy and the avoidance of normal tissues also means that we may be able to prescribe higher radiation doses to the tumour. For clinicians and scientists, the diagnostic power of MRI scanning will allow them to use the MR Linac to develop new approaches to modify the pattern of radiation delivery such that extra dose can be deposited in tumour areas that pose the greatest threat to the patient. Such areas can be identified using so-called functional imaging techniques on an MRI scanner."

Technical Summary

Effective conformal radiotherapy requires identification of the tumour's extent and dose delivery that is precise in space and time throughout the treatment course. Current state-of-the-art technology used to achieve this goal comprises treatment integrated X-ray imaging (eg cone-beam CT, X-ray fluoroscopy) allowing 3D-imaging immediately before treatment, or acquisition of 2D-X-ray projections of moving targets during treatment. The treatment-integrated X-ray imaging strategy
suffers from disadvantages of relatively low contrast between different soft tissues, and the delivery of additional radiation dose to the patient. At ICR/RM we aim to develop the next generation of image-guided radiotherapy by replacing conventional X-ray-guidance with treatment-integrated magnetic resonance image (MRI)-guided therapy (MRIgRT). The ability to use the superior soft-tissue contrast of MRI in real-time during treatment will revolutionize current clinical radiotherapy practice.
This research proposal focuses on developing MRIgRT using an MR Linac. This will permit clinical exploitation of the three major physical advantages of MRIgRT: excellent soft tissue contrast; avoidance of any additional imaging-dose; realtime/on-line MR guidance of the radiation beam. In order to do this, the physics-related research will optimise geometrical
accuracy and imaging sequences for the MR component of the technology, establish dosimetry and treatment verification methodologies, develop MRI-based treatment planning for a range of different tumour sites and solve the problem of realtime
MRI guidance of radiotherapy. Thereafter, we will conduct early-phase clinical studies to include safety and efficacy endpoints in different tumour sites. Specifically, we will study the benefits of enhanced soft tissue contrast in pelvic tumours, organ motion and tissue function management in lung tumours and motion management and avoidance of
imaging dose in paediatric tumours.

Publications

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Guerreiro F (2017) Evaluation of a multi-atlas CT synthesis approach for MRI-only radiotherapy treatment planning. in Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)

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Panek R (2017) Noninvasive Imaging of Cycling Hypoxia in Head and Neck Cancer Using Intrinsic Susceptibility MRI. in Clinical cancer research : an official journal of the American Association for Cancer Research