General

There is a variety of ionizing radiation beams used in radiotherapy. They range from low energy x-rays involving accelerating voltages as low as 10 kV to megavoltage x-ray beams with equivalent accelerating potentials of up to 25 MV. Electron particle beams in the 4 to 20 MeV energy range are also used. Electron beams and gamma ray beams have also been derived from radioactive sources. The most notable source still being used for a gamma ray beam is cobalt-60.

Neutron beams, proton beams and light ion beams have also been used. At present, neutron beams are no longer widely used, although advantages now recognized with proton and light ion beams have led to an escalation in the number of facilities being set up throughout the world for their clinical use. In addition, there are also development programs to improve our understanding of the absolute dose and of the radiobiological effect of these beams.

Radiotherapy treatment is dominated by the use of x-ray beams, in particular, megavoltage beams between 4 MV and 25 MV, although many of the linear accelerators which produce the megavoltage x-ray beams can also deliver electron beams. Today, the most commonly used treatment delivery system is the linear accelerator which can produce both photon and electron beams. This chapter deals with x-ray and electron beams and their production and also contains a small section on gamma ray beams.

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