Total-skin electron therapy is used in the treatment of mycosis fungoides, a T-cell lymphoma.
Large fields and large source to patient distances (>200 cm) are used.
It is important to calculate dose distributions for high angles of incidence.
Under these conditions, divergence of the beam over the electron range ( 2 cm) is negligible (<1%) enabling a useful geometrical variance reduction technique, the reciprocity theorem, which substitutes a parallel beam of a large diameter with a point source scored in a detector region of large diameter.