| Abstract [eng] |
Adaptive treatment planning using a device that integrates magnetic resonance imaging (MRI) and a radiation therapy unit is the key development in radiation oncology to further improve targeted dose delivery and avoid complications, since MRI provides excellent soft-tissue visualization. The designs of these modalities aim to produce simultaneous and unimpeded operation of an MRI and a medical linear accelerator. However, the presence of a magnetic field influences the response of radiation detectors due to the Lorentz force acting on the secondary electrons. The objective of this project was to determine the response of three recently developed MR-compatible ionization chambers in magnetic fields of different field strengths and field orientations. The response of the MR-compatible Exradin ionization chambers was investigated both by means of experiments and simulations. For the magnetic field perpendicular to photon beam and ion chamber axis, both experiments and simulations could be conducted, and the experimental measurements showed good agreement with the simulation results. In this orientation, the measured chamber response showed a significant increase with magnetic flux density. Simulations only were carried out for the other two orientations: the magnetic field parallel to the chamber axis as well as parallel to the beam. There was very little change in chamber response for all magnetic flux densities in both orientations. Overall, the chamber response in a magnetic field could be modelled well using EGSnrc Monte-Carlo simulations within measurement accuracy. |
