Linear energy transfer (LET)

Linear energy transfer is the average (radiation) energy deposited per unit path length along the track of an ionizing particle. Its units are keV/μm.

Linear energy transfer describes the energy deposition density of a particular type of radiation, which largely determines the biological consequence of radiation exposure.

The linear energy transfer of a charged particle is ∞ Q/Ek

• linear energy transfer is proportional to the square of the charge of the particle
• linear energy transfer is inversely proportional to the particle's kinetic energy

High linear energy transfer radiations: linear energy transfer 3-200 keV/μm

• commonly mediated by:
  • α-particles
  • protons
  • neutrons
• greater density of interactions at cellular level
• more likely, than low linear energy transfer, to produce biological damage in a given volume of tissue

Low linear energy transfer radiations: linear energy transfer 0.2-3 keV/μm

• commonly mediated by:
  • electrons
  • positrons
  • gamma rays
  • x-rays
• less likely than high linear energy transfer to produce tissue damage in the same volume of tissue