Design of electron beam wedges for increasing the penumbra of abutting fields

Polystyrene electron beam wedges increase the beam penumbra of electron beams and can reduce the dose non-uniformity of field junctions of abutted adjacent electron fields. The authors have investigated the dependence of the electron beam penumbra on the physical angle of polystyrene wedges for various electron beam energies and field sizes. Square, individual, and uniformly thick (1-15 mm) polystyrene inserts which covered the entire field were placed in electron applicators. Beam profiles, central-axis depth doses, and isodose curves were obtained using a water-phantom scanning system. The dependence of the beam penumbra widths, beam energy and practical range on the thickness of the polystyrene inserts are reported. These data yield the design parameters for polystyrene physical wedge angles which would increase beam penumbra from about 15 mm to about 35 mm.