Limitations of retracted missing tissue compensators: an experimental analysis.

The introduction of an attenuating medium into a photon beam serves both to reduce the intensity of the primary beam and to create secondary radiation due to scatter. When retracted missing tissue compensators are employed to compensate for irregular surface geometry or internal inhomogeneities they are almost always fabricated without regard to the scattered radiation that they introduce to the system. Analysis of such a retracted compensator designed for use with an anthropomorphic phantom reveals an inability to provide true compensation. Subsequent analysis of a mathematically describable conical geometry demonstrates the need for improved compensator design.