ABSTRACT
The feature that makes electron beams very useful for a range of clinical applications is the
shape of the depth dose curve. This allows for relatively uniform dose delivery to reasonably
well-defined regions from the surface to the therapeutic range, with sparing of underlying
tissue due to the rapid reduction of the dose towards the practical range. At about 20 MeV
and above, the gradient of the depth dose curve begins to lose the characteristic steepness seen
at lower energies and the separation of the high-dose and spared regions becomes increasingly
blurred. Energies higher than this can be used for deep-seated tumours, but the techniques
begin to approach those used for megavoltage photons. However, the majority of linear
accelerators that provide clinical electron beams produce energies within the range 4 MeV
to 20 MeV; this section concentrates primarily on their use. Electron beams of these energies
deliver high doses (greater than about 90% depth dose) to depths of around 1cm to 6 cm.
Common applications include skin and lip cancers, chest wall and peripheral lymphatic areas in
breast cancer, additional boost doses to limited volumes such as scar areas and nodes, various
head and neck cancers and other sites lying within these depths of the surface. The most
commonly used beams are those of medium energy.
