{"entity":{"id":"linear-energy-transfer","kind":"term","name":"Linear energy transfer (LET)","aka":[],"tldr":"A measure of how densely a particle of radiation deposits its energy as it travels through tissue. Alpha particles dump their energy in a short, dense burst; beta particles and gamma rays spread it thinly over a much longer track.","summary":"Linear energy transfer (L or LET) is the average energy that a charged ionising particle transfers to the medium per unit length of its track, L = dE/dl, expressed in keV per micrometre (keV/µm). It describes the spatial density of energy deposition (and therefore of ionisation events) along a particle's path, which is what ultimately determines the biological severity of the damage caused for a given absorbed dose.\n\nRepresentative values illustrate the range: cobalt-60 gamma rays and diagnostic x-rays are low-LET (roughly 0.2-2 keV/µm), beta particles from radionuclides such as lutetium-177 are also low-LET (a 1 MeV beta particle deposits roughly 0.2 keV/µm and travels several millimetres), while alpha particles are high-LET, depositing on the order of 80-150 keV/µm over a track of only tens to about a hundred micrometres (a handful of cell diameters). High-LET radiation causes densely clustered ionisations that produce more complex, harder-to-repair DNA double-strand breaks than the sparse ionisation from low-LET beta or gamma radiation, which is the physical basis for targeted alpha therapy's distinct toxicity and efficacy profile compared with beta-emitting radioligand therapy.\n\nLET is the mechanistic quantity underlying both the regulatory radiation weighting factor used in equivalent dose (wR = 20 for alpha versus 1 for beta/gamma) and the empirically measured relative biological effectiveness used to compare therapeutic effect between alpha- and beta-emitting radiopharmaceuticals.","asOf":"2026-09-22","links":[{"label":"NRC training materials: interaction of charged particles with matter, LET and stopping power","url":"https://www.nrc.gov/docs/ml1122/ml11229a666.pdf"},{"label":"ScienceDirect Topics: linear energy transfer, representative values","url":"https://www.sciencedirect.com/topics/immunology-and-microbiology/linear-energy-transfer"}],"tags":[],"related":["relative-biological-effectiveness","equivalent-dose","alpha-vs-beta","lu-177"],"indications":[],"sections":[],"technologies":["targeted-alpha-therapy","radioligand-therapy","auger-electron-therapy"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"category":"physics"},"route":"/terms/linear-energy-transfer/","neighbours":{"term":[{"id":"absorbed-dose-term","kind":"term","name":"Absorbed dose and the gray (Gy)","route":"/terms/absorbed-dose-term/"},{"id":"alpha-vs-beta","kind":"term","name":"Alpha vs beta emitters","route":"/terms/alpha-vs-beta/"},{"id":"equivalent-dose","kind":"term","name":"Equivalent dose and effective dose (sievert)","route":"/terms/equivalent-dose/"},{"id":"relative-biological-effectiveness","kind":"term","name":"Relative biological effectiveness (RBE)","route":"/terms/relative-biological-effectiveness/"}],"isotope":[{"id":"lu-177","kind":"isotope","name":"Lutetium-177","route":"/isotopes/lu-177/"}],"technology":[{"id":"auger-electron-therapy","kind":"technology","name":"Auger-electron therapy","route":"/technologies/auger-electron-therapy/"},{"id":"radioligand-therapy","kind":"technology","name":"Radioligand therapy (beta emitters)","route":"/technologies/radioligand-therapy/"},{"id":"targeted-alpha-therapy","kind":"technology","name":"Targeted alpha therapy","route":"/technologies/targeted-alpha-therapy/"}]}}