The clinical introduction of magnetic resonance imaging guided radiotherapy has prompted consideration of the potential impact of the static magnetic field on biological responses to radiation. This review provides an introduction to the mechanisms of biological interaction of radiation and magnetic fields individually, in addition to a description of the magnetic field effects on megavoltage photon beams at the macroscale, microscale and nanoscale arising from the Lorentz force on secondary charged particles.

A relatively small number of scientific studies have measured the impact of combined static magnetic fields and ionising radiation on biological endpoints of relevance to radiotherapy. Approximately half of these investigations found that static magnetic fields in combination with ionising radiation produced a significantly different outcome compared with ionising radiation alone. MRI strength static magnetic fields appear to modestly influence the radiation response via a mechanism distinct from modification to the dose distribution. This review intends to serve as a reference for future biological studies, such that understanding of static magnetic field plus ionising radiation synergism may be improved, and if necessary, accounted for in magnetic resonance imaging guided radiotherapy treatment planning.