Magnetic resonance guided radiotherapy (MRgRT) shows great potential for the further improvement of cancer treatment. It offers increased accuracy in defining the target and organs at risk as well as real-time imaging for online verification of dose delivery, online adaptation and treatment optimisation.
However, MRgRT requires measurement of dose and dose distributions in the presence of a magnetic field, which currently decreases dosimetrical accuracy considerably. In MRgRT, the role of CT images in conventional radiotherapy will be replaced by MRI, which poses other and higher demands on the geometrical accuracy of MR images. Both these factors are still holding back the wide-scale clinical implementation of this promising technique.
To allow for the widespread clinical implementation of MR guided radiotherapy for cancer treatment, capabilities to measure both the influence of the magnetic field on the detectors and the radiation beam dose distribution must be developed. Geometrical accuracy of the images used in treatment planning is essential in delivering dose distributions to the patient as intended.
In this Joint Research Project experts and practitioners from various disciplines in medical physics and metrology are working together on the metrological framework and methodologies for accurate dose delivery and MR imaging.
The evolution of MRgRT has only just started in the context of academic centres. The impact of this project on this evolution the coming years and on European healthcare in general will be high. More specifically, it will impact the following developments:
- A harmonised metrological framework will be in place for quality assurance to enhance consistency in multi-centre clinical trials organised to investigate the clinical benefits of MRgRT.
- Ultimately, 0.7 – 1.2 million European cancer patients annually will have access to MRgRT and will potentially benefit from increased life expectancy and enhanced quality of life.
- MRgRT is a potential non-invasive treatment for a range of cancers, for which conventional radiotherapy, to date, has proved inadequate due to organ movements. The eligibility of these tumour sites for MRgRT will be investigated.
- The competitiveness of European manufacturers of MRgRT facilities and detector equipment will increase.
Metrological and scientific impact
On a metrological and scientific level, this project will lead to:
- Traceability of clinical reference dosimetry for MRgRT to primary standards.
- Fundamental dosimetrical concepts to validate MC codes for radiation transport in the presence of magnetic fields.
- Novel concepts of QA using MR compatible phantoms and methods to determine treatment safety margins for MR based dose delivery.
The ultimate goal of this Joint Research Project is the safe clinical implementation and support of future innovations in MR guided radiotherapy (MRgRT) by developing the metrological capacity in dosimetry and imaging.
The specific scientific and technical objectives of this project are:
- To develop a metrological framework of primary and secondary standards for traceable dosimetry under reference conditions for MR guided radiotherapy, which will form the basis of future dosimetry protocols (CoPs). This will include determining input data and establishing a formalism for reference dosimetry.
- To develop methodologies for measuring treatment planning system (TPS) input data for MR guided radiotherapy. This should include the determination of detector characteristics for commercially available detector systems and secondary standards in hybrid fields. It also includes characterisation of the radiation field based on measurements and Monte Carlo modelling.
- To develop methodologies to assess the accuracy of the Monte Carlo based radiation transport algorithms in external magnetic fields.
- To evaluate MR based dose delivery under static and dynamic conditions.
- To facilitate the uptake up of recommendations for dosimetry and MR related quality assurance of MR guided radiotherapy developed in the project by clinicians and industry in order to enable hospitals to perform quality assurance based on traceable measurements and support improvements for dosimetry in MRgRT.
To achieve the goals, the following work packages have been determined: