Surface dose and build-up region measurements with wedge filters for 6 and 18 MV photon beams

High-energy photons are most commonly used in radiotherapy to treat cancer. Wedge filters are required to obtain homogeneous dose distribution in the patient. Different wedge filter types create different surface doses. In this study, the effect of the virtual and physical wedge filters on the surface and build-up region doses was examined for 6- and 18-MV high-energy photon beams.

The measurements were made in a water equivalent phantom in the build-up region at a 100-cm source-to-surface distance for various field sizes using virtual and physical wedge filters having different angles. A parallel-plate ion chamber was used to measure the percent depth doses.

The percentage dose at the surface increased as the field size increased for open, virtual, and physical wedged beams. For open, physical, and virtual wedged beams, the surface doses were found to be 15.4%, 9.9%, and 15.9% with 6-MV photons and 10.6%, 8.8%, 11.9% with 18-MV photons, respectively, at 10 x 10 cm(2) field size.

Build-up doses of virtual wedged beams were similar to those of open beams. Surface and buildup doses of physical wedged beams were lower than those of open and virtual wedged beams.