Which term describes the energy deposited by radiation along its path per unit length?

• A. Relative Biological Effectiveness (RBE)
• B. Linear Energy Transfer (LET)
• C. Radiation Weighting Factor (Wr)
• D. Oxygen Enhancement Ratio (OER)

Answer: (B)

Linear energy transfer describes the energy deposited by radiation along its path per unit length. It measures how densely energy is deposited as the particle travels through matter, typically in units like keV per micrometer. This density of energy deposition helps explain the type of biological damage: high-LET radiations (dense energy tracks) tend to cause complex, clustered damage that’s harder to repair, while low-LET radiations (sparser tracks) tend to produce more repairable damage.

Other terms don’t capture this path-length energy density. Relative Biological Effectiveness compares biological outcomes at the same dose across different radiations, not how energy is laid down along the track. Radiation weighting factor adjusts dose to an equivalent dose for protection purposes, not the deposition pattern. Oxygen enhancement ratio describes how oxygen presence changes biological effect, again not the energy deposition along the track.