Quality assurance

QA for MRI-based radiotherapy

The MRI scanners of today have been developed for making diagnoses. When the MRI images are instead to be used as a basis for planning radiotherapy, new demands are made of the image quality. This project will therefore identify all steps of the process and develop methods for quality assurance.

The MRI scanner has limitations where producing an exact map of the body in 3D is concerned, and this results in certain deviations from reality, known as geometric distortions. Furthermore, the system’s ability to accurately map the body is affected by patient movements. The limitations of magnetic resonance imaging (MRI) in terms of geometric accuracy are caused by the system’s magnetic field and the use of gradients.

The geometric accuracy has had no great significance in diagnostics, but is even more important if the images are to be used to locate tumours prior to radiotherapy.

New usage places new demands on the technology

The signal in an MRI image is built up in a complex manner; one which cannot easily be translated into physical quantity such as “electron density” in computed tomography (CT), i.e. the imaging technology most commonly used today. MRI images can therefore not be used as a basis to calculate a sufficiently high dose of radiation that will allow treatment with as few side effects as possible. MRI can, however, map and delimit tumours in a much clearer manner than CT information.

All of this combined means that it is important to carefully observe the quality assurance aspect when radiotherapy is based on MRI data.

Participants in the project include representatives for Sweden’s university hospitals, Siemens, Elekta, ScandiDos and representatives for the County Hospital in Gävle, Jönköping and Sundsvall.