Scattered photons produced by beam-modifying filters.
When a beam-modifying filter such as a wedge or a compensator is placed in an x-ray beam, scattered photons are generated in the filter material. The magnitude of the dose contribution from these photons for a 4-MV x-ray beam was measured. At a distance of 30 cm from the filter, a copper sheet of 1-cm thickness produced a dose contribution on the centerline of about 6% of the transmitted primary dose in a 20 X 20 cm2 field. At the edges of the beam, this contribution was only about one-half that on the centerline. The presence of these scattered photons leads to only minor dose errors in clinical applications if simple procedures are followed to account for their contribution.
D006801:Humans; D011827:Radiation; D011878:Radiotherapy / Q000295:instrumentation / Q000379:methods*; D012542:Scattering, Radiation; D014965:X-Rays