title: An apparatus for applying strong longitudinal magnetic fields to clinical photon and electron beams.
abstract: Monte Carlo studies have recently renewed interest in the use of the effect of strong transverse and longitudinal magnetic fields to manipulate the dose characteristics of clinical photon and electron beams. A 3.5 T superconducting solenoidal magnet was used to evaluate the effect of a longitudinal field on both photon and electron beams. This note describes the apparatus and demonstrates some of the effects on the beam trajectory and dose distributions for measurements in a homogeneous phantom. The effects were studied using film in air and in phantoms which fit in the magnet bore. The magnetic field focused and collimated the electron beams. The converging, non-uniform field confined the beam and caused it to converge with increasing depth in the phantom. Due to the field's collecting and focusing effect, the beam flux density increased, leading to increased dose deposition near the magnetic axis, especially near the surface of the phantom. This study illustrates some benefits and challenges associated with the use of non-uniform longitudinal magnetic fields in conjunction with clinical electron and photon beams.
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor 48109-0010, USA. litzen@umich.edu
authors.forename: D W
authors.initials: DW
authors.lastname: Litzenberg
authors.forename: B A
authors.initials: BA
authors.lastname: Fraass
authors.forename: D L
authors.initials: DL
authors.lastname: McShan
authors.forename: T W
authors.initials: TW
authors.lastname: O'Donnell
authors.forename: D A
authors.initials: DA
authors.lastname: Roberts
authors.forename: F D
authors.initials: FD
authors.lastname: Becchetti
authors.forename: A F
authors.initials: AF
authors.lastname: Bielajew
authors.forename: J M
authors.initials: JM
authors.lastname: Moran
mesh_terms: D004583:Electrons / Q000627:therapeutic use; D008280:Magnetics; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D011882:Radiotherapy, High-Energy