ABSTRACT
The electron beams most commonly available in radiotherapy departments have energies
of between 4 MeV and 25 MeV as produced by standard clinical linear accelerators, although
some microtrons provide higher energies. Electron beams have advantages for a variety of
clinical situations due to the characteristics of their depth-dose curves (Figure 24.1). They
deliver acceptably uniform doses to a relatively well-defined region extending from the surface
to the therapeutic range (taken as the distal 85% or 90%), which can be altered to fit the clinical
situation by varying the beam energy, followed by a steep fall in relative dose that spares
underlying structures. The general approach to electron-beam measurement and dosimetry
is similar to that for megavoltage x-ray beams. However, there are a number of significant
differences:
The basic physics relating to electron interactions has been discussed previously
(Chapter 3) and additional material can be found in ICRU (1984) and Klevenhagen
(1985, 1993). In this chapter, the characteristics of clinical electron beams are described.
