higherLET

HigherLET refers to radiation with a greater linear energy transfer (LET) than other forms of radiation. LET is the average energy deposited per unit length of tissue along the particle’s path and is typically expressed in keV per micrometer (keV/μm). Higher-LET radiation deposits energy more densely along its track than lower-LET radiation.

Biological effects tend to be more severe for higher-LET radiation because the dense ionization causes complex DNA damage, such as clustered double-strand breaks, which are harder for cells to repair. This often results in a higher relative biological effectiveness (RBE) per unit of absorbed dose compared with low-LET radiation. Low-LET radiation, such as X-rays and gamma rays, produces more sparsely distributed damage that is more readily repaired by cellular processes.

LET is not uniform along the track of many radiations. For charged particles, LET typically increases toward the end of their range, creating a high-LET region near the Bragg peak. This characteristic underpins the use of high-LET radiations, such as heavy ions, in certain forms of radiotherapy, enabling increased biological impact within the tumor while reducing exposure to tissue on entry.

Measurement and application of LET involve dose-averaged LET calculations, track-structure simulations, and Monte Carlo methods. In radioprotection, LET informs quality factors used to convert absorbed dose to dose equivalents, reflecting differing biological risks. The impact of higher LET also depends on dose, fractionation, tissue type, and oxygenation, with high-LET radiation generally being less dependent on oxygenation than low-LET radiation.

Common examples of higher-LET radiations include alpha particles and heavy ions used in particle therapy, as well as neutrons that generate secondary high-LET charged particles.