Magnetic Fields with Photon Beams
The use of magnetic fields with photon beams is based on two well-known facts: what actually deposits energy (dose) to the irradiated material (the patient) is the secondary electrons and positrons resulting from Compton and pair-production interactions of the primary and secondary photons in the beam with the atoms of the material; and high-energy electrons and positrons tend to curl around “lines of force” of a strong magnetic field, with the radius of curvature of such trajectories being inversely proportional to the strength of the magnetic field. Therefore a magnetic field with a strong transverse component (i.e., transverse to the direction of the photon beam) whose strength increases with increasing depth into the patient, should produce significant enhancement of photon-beam dose as the secondary electrons and positrons tend to pile up, for the charged particles released at smaller depths penetrate more deeply than those released deeper into the patient.
We have recently been studying this phenomenon, both theoretically and through EGS4 Monte Carlo calculations, and have published three articles on it :
David Jette, "Magnetic Fields with Photon Beams: Dose Calculation Using Electron Multiple-Scattering Theory", Med. Phys. 27(8), 1705-1716 (August 2000).
David Jette, "Magnetic Fields with Photon Beams: Monte Carlo Calculations for a Model Magnetic Field", Med. Phys. 27(12), 2726-2738 (December 2000).
David Jette, "Magnetic Fields with Photon Beams: Use of Circular Current Loops", Med. Phys. 28(10), 2129-2138 (October 2001).
An example of this dose enhancement was published on the front cover of the issue of Medical Physics in which the second article appeared.