A beam spoiler is a piece of material, placed into the path of the

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...

beam in

radiotherapy Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radia ...

. The purpose of the spoiler is to reduce the depth of the maximum radiation dosage.Bentel, G.C. (1996) ''Radiation therapy planning'
p.103.
McGraw-Hill Professional Retrieved September 2011.

Composition

The beam spoiler is composed of a sheet of material which has a low

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...

,Specht, L., Yahalom, J. (2010) ''Radiotherapy for Hodgkin Lymphoma'
p.125.
Springer. Retrieved September 2011 typically

lucite Poly(methyl methacrylate) (PMMA) belongs to a group of materials called engineering plastics. It is a transparent thermoplastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Plexiglas, Acrylite, ...

, the thickness of which is varied according to the beam energy and the distance by which the radiation dose must be shifted.

Action

As the primary photon beam passes through the plate, secondary

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

s are generated. The beam exiting the spoiler is a combination of the spoiler-attenuated photons and the spoiler-generated electrons. The electron component 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.

References

Radiobiology {{medical-equipment-stub