Electron-Beam Treatment Planning Techniques

Authored by: Alan McKenzie , David Thwaites

Handbook of Radiotherapy Physics

Print publication date:  June  2007
Online publication date:  June  2007

Print ISBN: 9780750308601
eBook ISBN: 9781420012026
Adobe ISBN:

10.1201/9781420012026.ch34

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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.

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