2: Introduction To Photon Beam Radiotherapy

Photon beams are the most commonly used ionising radiation modality in the world. There are three methods of production:

  • By an x-ray tube (Superficial or Orthovoltage beams)
  • By a radioactive source (Teletherapy)
  • By a linear accelerator

For the foundation level of knowledge, the construction and function of a simple x-ray tube is required. This leads on to understand the construction of a linear accelerator, which uses some similar principles but with added awesomeness. How each machine generates a useful beam of photons is also important.
The other important topic to cover early on is the basic properties of a photon beam. This is not knowledge of depth dose curves, output factors and so on, but rather the spectrum of the beam, the need for filtration and methods for modifying the output of the beam.