From the front cover of Medical Physics of December 2000 (vol. 27, no. 12):
Central-plane dose distributions for a 6x6 cm2 30-MV photon beam
penetrating a water phantom from the left. In the lower figure a magnetic
field with center strength of 3 T is applied three times in succession,
displaced longitudinally by 2 cm each time. (Doing this broadens the
region of very high dose enhancement longitudinally.) The normalization is
such that the same total amount of beam energy is deposited in the patient with
and without a magnetic field; the difference is the great concentration of dose
at the presumed tumor site, when a magnetic field is used.