What effect does an increase in linear energy transfer (LET) have on relative biologic effectiveness (RBE)?

An increase in linear energy transfer (LET) is associated with an increase in relative biologic effectiveness (RBE). LET refers to the amount of energy that radiation transfers to the material it passes through per unit distance, and it is generally higher for more densely ionizing radiation, such as alpha particles, compared to low LET radiation, like X-rays or gamma rays.

As LET increases, the ionization effects on biological tissues become more significant. This means that high-LET radiation inflicts more damage per unit of absorbed dose, primarily because it produces more clustered or complex damage to DNA and other critical cellular structures. This kind of damage is more difficult for the cell to repair than the damage caused by low-LET radiation.

Consequently, the RBE, which is a measure of the biological effectiveness of different types of radiation compared to a standard reference (usually X-rays), will increase with higher LET. Therefore, as the radiation becomes more effective in causing biological harm, the RBE rises, indicating that less dose is needed to achieve the same biological effect compared to low LET types of radiation. This relationship highlights the importance of understanding LET and RBE in radiological protection and therapy.