An apparatus for applying strong longitudinal magnetic fields to clinical photon and electron beams

Monte Carlo studies have recently renewed interest in the use of the effect of strong transverse and longitudinal magnetic fields to manipulate the do se characteristics of clinical photon and electron beams. A 3.5 T supercond ucting 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 distri butions 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 convergin g, non-uniform field confined the beam and caused it to converge with incre asing depth in the phantom. Due to the field's collecting and focusing effe ct, the beam flux density increased, leading to increased dose deposition n ear the magnetic axis, especially near the surface of the phantom. This stu dy illustrates some benefits and challenges associated with the use of non- uniform longitudinal magnetic fields in conjunction with clinical electron and photon beams.