Linear energy transfer (LET)
How densely a radiation track dumps energy along its path. Sparse tracks (X-rays, most of a proton beam) are easier to repair; dense tracks (the proton's stop-point, carbon ions, alpha particles) punch clustered holes in DNA.
Overview
Linear energy transfer is the energy a charged particle deposits per unit length of track, usually in keV per micrometre. Photons and electrons are low-LET. Protons are mostly low-LET along the entrance plateau and rise at the Bragg peak and just beyond it, which is why a constant relative biological effectiveness of 1.1 is only a reporting convention. Carbon ions and alpha particles (around 100 keV per micrometre) are high-LET: they cause clustered double-strand breaks, work in hypoxia, and are less sensitive to fraction size. LET is the physical input to relative biological effectiveness; the two are not the same number.
- Proton beam
- Bragg peak
- No exit dose
Showing the technology this term belongs to: Proton therapy.
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