Bragg peak
The spot where a proton or carbon-ion beam dumps most of its energy and then stops, so tissue behind the tumour gets almost no dose.
Overview
A charged particle slows as it travels through tissue and deposits most of its energy in a narrow peak just before it stops. That Bragg peak is why protons and carbon ions have no exit dose compared with X-rays. The spread-out Bragg peak stacks several energies to cover a tumour's depth. Linear energy transfer, and therefore relative biological effectiveness, is highest at the distal edge of the peak, which is why a constant proton RBE of 1.1 can understate dose just beyond the target. Range uncertainty of a few millimetres is the planning counterpart of that edge.
- Proton beam
- Bragg peak
- No exit dose
Showing the technology this term belongs to: Proton therapy.
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