Medical physics Question:

A beam spoiler is a piece of material, such as a 1-cm-thick lucite or polystyrene plate, placed into the path of the photon beam. As the primary photon beam passes through the plate, secondary electrons are generated. The beam which exits the spoiler is a combination of the spoiler-attenuated photons and the spoiler-generated electrons. The electron component of a spoiled photon beam alters the depth dose in the buildup region in a way that depends on the photon beam energy, the field size, and the distance of the spoiler from the treatment surface.