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. Currently, the number of clinical MR-guided X-ray Therapy (MRgXT) facilities (combining X-ray beams and MRI) is increasing rapidly. However, full clinical utilization is hampered by the lack of standards for small field dosimetry. Although not as advanced clinically, future developments are also being made with MR-guided Proton Therapy (MRgPT) which combines proton beams and MRI. To show the feasibility of dose delivery with MRgPT and to prepare for (pre)-clinical investigations, industry and academia need traceable methods for dosimetry.


In this Joint Research Project experts and practitioners from various disciplines in medical physics and metrology are working together on traceable small field dosimetry for MRgRT.

Essential for the development of standards for small field dosimetry are the methodology and data sets of correction factors. Since dosimetry in MRgRT has to be performed in the presence of a strong magnetic field, capabilities will be developed to measure in small radiation fields both the influence of the magnetic field on the detectors and the radiation beam dose distribution.

The evolution of MRgRT has only just started in the context of academic centres. The impact of this project on this evolution and on European healthcare in general will be high. More specifically, this project will impact the following developments in the coming years:

  • Acceleration of the development of standards for small field dosimetry in MRgRT will enable hospitals to perform traceable small field dosimetry in MRgRT.
  • Manufacturers of detectors and measurement equipment will be able to assess the quality of their products for MRgRT.
  • 7M European cancer patients annually (50% of RT patients) will have increased life expectancy and quality of life.
  • Enabling translation of MRgPT prototypes to clinical setting.

Metrological and scientific impact

On a metrological and scientific level, this project will lead to:

  • Traceability of clinical small field dosimetry for MRgRT to primary standards.
  • Fundamental dosimetrical concepts to validate Monte Carlo codes for radiation transport in the presence of magnetic fields.
  • Understanding of the response of detector in the presence of magnetic fields


The ultimate goal of this Joint Research Project is to support future standards for small field dosimetry in MRgRT by the development of traceable measurement methods for dosimetry in small x-ray (photon) and proton beams (field size < 3 cm) in the presence of strong magnetic fields.

The specific scientific and technical objectives of this project are:

  • The development of a method for traceable dose measurement in MRgPT;
  • To investigate radiation field characteristics and detector responses by Monte Carlo simulations and experiments for x-ray and proton beams in the presence of magnetic fields;
  • The development of a methodology and dataset of traceable measured correction factors for small field dosimetry for MRgXT compatible with TRS-483.

To achieve the goals, the following work packages have been determined:

In this work package we will provide the necessary knowledge, recommendations, methodology and data to extend this existing Code of Practice for dosimetry of small fields in conventional radiotherapy to be applicable in MRgXT and investigate its adoption in MRgPT.

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The aim of work package 2 is to design and carry out Monte Carlo simulations of beam geometries and detector response, in order to inform the investigation of small field characteristics in MRgXT and MRgPT.

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The aim of this work package is to provide the experimental data for small photon fields in the presence of magnetic fields, in order to inform the investigation of small field characteristics in MRgXT and to contribute to the data set of correction factors in WP1.

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The aim of this work package is to perform comprehensive measurements of proton beam characteristics and detector properties in the presence of magnetic fields for the purpose of a traceable method for dosimetry in MRgPT facilities.

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The aim of this work package is to ensure the wide dissemination of the knowledge generated within this project.

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The project runs until 2023.