RBE relative biological

RBE Relative biological effectiveness. Ratio of the biological e ect of a given amount of radiation to that produced by tiie same amoimt of low-energy radiation (see Table 2-4). 

The intensity of radiation depends on the number of disintegrations as well as on the energy and type of radiation emitted. One common unit for the absorbed dose of radiation is the rad (radiation absorbed dose), which is the amount of radiation that results in the absorption of 1 X 10 J per gram of irradiated material. The biological effect of radiation depends on the part of the body irradiated and the type of radiation. For this reason, the rad is often multiplied by a factor called the RBE (relative biological effectiveness). The product is called a rem (roentgen equivalent for man) ... 

The dose of radiation absorbed by a unit of mass per unit of time is called the absorbed dose rate in units of joules/kg. The rad (radiation absorbed dose) is 10 J/kg. A rad of a rays is more harmful than a rad of rays. Hence, the RBE (relative biological effectiveness) of radiation can normalize the damage to tissue by different types of radiation. This is illustrated by the equation... 

Note RBE, relative biological effectiveness compared with standard (250 keV x-ray) radiation. 

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