Oxygen Effect, Relative Biological Effectiveness and Linear Energy Transfer

Abstract

Oxygen is one of the most effective dose-modifying agents. Oxygen causes “fixation” of radiation-induced DNA damage. The oxygen enhancement ratio (OER) is equal to the ratio of doses of radiation (hypoxic over oxic) required to achieve the same biological effect. Similarly, effectiveness of different types of radiation can be assessed by determining the ratio of doses required to achieve the same effect. This number is called relative biological effectiveness (RBE). Linear energy transfer (LET) is the density of ionizations deposited by each radiation type along its track. As LET increases, OER decreases until it becomes 1 (e.g., there is no oxygen effect). As LET increases, RBE increases up to a point (100 KeV/μm), and then declines due to the “overkill effect.”