Magnetic fields with photon beams: dose calculation using electron multiple-scattering theory.
Strong transverse magnetic fields can produce large dose enhancements and reductions in localized regions of a patient under irradiation by a photon beam. We have developed a new equation of motion for the transport of charged particles in an arbitrary magnetic field, incorporating both energy loss and multiple scattering. Key to modeling the latter process is a new concept, that of "typical scattered particles." The formulas which we have arrived at are particularly applicable to the transport of, and deposition of energy by, Compton electrons and pair-production electrons and positrons generated within a medium by a photon beam, and we have shown qualitatively how large dose enhancements and reductions can occur. A companion article examines this dose modification effect through systematic Monte Carlo simulations.
Jette
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The Lawrence H. Lanzl Institute of Medical Physics, Seattle, Washington 98103-0760, USA. dave@lanzl.com
D000465:Algorithms; D055592:Biophysical Phenomena; D001703:Biophysics; D004583:Electrons; D006801:Humans; D008280:Magnetics; D008962:Models, Theoretical; D009010:Monte Carlo Method; D016011:Normal Distribution; D017785:Photons / Q000627:therapeutic use*; D011874:Radiometry / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods; D012542:Scattering, Radiation