Ionizing Radiation relative biological effectiveness

Relative Biological Effectiveness (RBE)—The RBE is a factor used to compare the biological effectiveness of absorbed radiation doses (i.e., rad) due to different types of ionizing radiation. More specifically, it is the experimentally determined ratio of an absorbed dose of a radiation in question to the absorbed dose of a reference radiation (typically 60Co gamma rays or 200 keV x rays) required to produce an identical biological effect in a particular experimental organism or tissue (see Quality Factor). 

Relative biological effectiveness (RBE) The biological effectiveness of any type of ionizing radiation in producing a specific damage (i.e., leukemia, anemia, carcinogenicity). See Radiation dose. 

Roentgen equivalent man (rem) The amount of ionizing radiation of any type that produces the same damage to humans as 1 roentgen of radiation. One rem = 1 roentgen equivalent physical (rep)/relative biological effectiveness (RBE). In the latest nomenclature, 100 rem = 1 Sievert (Sv). 

Relative Biological Effectiveness (RBE) Factor used to compare the biological effectiveness of different types of ionizing radiation inverse ratio of the amount of absorbed radiation required to produce a given effect to a standard radiation required to produce the same effect. 

For radiation protection purposes, several theoretical dosimetric quantities have been created that attempt to normalize the responses of different tissues and organs of the body from irradiation by different types of ionizing radiation so that uniform radiation protection guidelines can be promulgated that are insensitive to the particulars of any given irradiation scenario. The traditionally used quantity has been the dose equivalent (DE), which is defined as the absorbed dose (D) multiplied by the quality factor Q. The unit of dose equivalent has been the rem, which is dimensionally the same as the rad the SI unit is the Sievert (Sv). Recently, the DE has been replaced by a similar concept called the equivalent dose. The equivalent dose depends on the relative biological effectiveness rather than on Q. 

Different kinds of radiation have different ionization efficiencies and are absorbed in different ways. In order to compensate for this the unit rem ( roentgen equivalent, man ) was introduced. It is defined as the quantity of radiation of any type which produces the same biological effect in man as that produced by 1 r of X-ray or y ray radiation. However, the biological effect depends upon the part of the body irradiated and on the type of radiation. This problem is dealt with by estimating a relative biological effectiveness (RBB), in relation to y-rays, for various parts of the body. For example, as far as the production of cataracts is concerned, 1 rad of fast neutrons is ten times as effective as 1 rad of y-rays. Thus if the eyes were... 

The fact drat radioisotopes decay to produce ionizing radiation does not influence their biological role. Radioisotopes are taken up and assimilated in the same way as are stable isotopes. Enzymes may be sufficiently sensitive to discriminate slightly between isotopes of the same element, leading to changes in relative isotopic abundance, but the effect is small (Marechal et al., 1999 Anbar et al., 2000 Marechal and Albarede, 2002 Zhu et al., 2002 Beard et al., 2003 Weiss et al.. 

Whereas nonionizing radiation is relatively harmless, ionizing radiation has a destructive effect on living tissue. When the atom that was ionized is part of a biological macromolecule or membrane component, the results can be devastating. 

Rem means a measure of the dose of any ionizing radiation to body tissue in terms of its estimated biological effect relative to a dose of 1 roentgen (r) of X-rays (1 millirem (mrem)=0.001 rem). The relation of the rem to other dose units depends upon the biological effect under consideration and upon the conditions for irradiation. Each of the following is considered to be equivalent to a dose of 1 rem ... 

---