LowLET

LowLET, short for low linear energy transfer, is a term used in radiobiology to describe ionizing radiation that deposits energy sparsely along its track in tissue. By convention, low-LET radiation has LET values of a few keV per micrometer or less, meaning the energy deposition along the particle’s path is relatively dispersed.

Common examples of low-LET radiation include X-rays, gamma rays, and beta particles. The exact LET depends on the particle type and its energy; photons used in diagnostic imaging and many external-beam therapies typically fall into the low-LET category, reflecting their greater penetrating power and more widely spaced ionizations.

In contrast, high-LET radiation deposits energy densely along short tracks and produces clustered or complex DNA damage. Examples include alpha particles and heavy ions. Because the energy is concentrated in small regions, high-LET radiation is usually more efficient at killing cells per unit absorbed dose and tends to cause damage that is harder to repair.

Biological effects differ accordingly. Low-LET damage is often sublethal and relies on indirect effects through free radicals; its relative biological effectiveness (RBE) is around 1 for many end points, though it can vary with dose, tissue, and endpoint. Clinically, low-LET photons are commonly used in external beam radiotherapy, while higher-LET modalities (such as certain ion therapies) exploit greater biological effectiveness to improve tumor control.

LET is measured as energy deposited per unit track length, in units of keV/μm. It is not a fixed property of a radiation type alone but varies with energy, medium, and experimental conditions.