Relative biological effectiveness

Relative biological effectiveness (RBE) - characteristics, adopted to map the biological effects of different types of ionizing radiation. Until recently RBE used in radiobiological research, and in the practice of radiation protection. The coefficient RBE is the ratio of the corresponding value of biological efficiency of radiation to the effect of x-rays or ' -radiation [average specific ionization 100 pairs of ions on microns ways in water or in a linear energy transfer (let) not over 3.5 Kev on microns ways in water] for specific biological systems, consider biological effect and the specific conditions under which use this type of radiation.
ToRBE = Etc/DFS
where Al - absorbed dose x-rays or ' -radiation, DH - absorbed dose of the investigational type of radiation that causes the same biological effect.
If per unit to take efficiency ' -radiation, the RBE coefficients of other types of radiation are found within the following limits: x-ray radiation (180-250 kV) - 1,2-2; bremsstrahlung with energies 1-70 MeV -0,5-1;?-radiation tritium (when inside the body) -1,3-1,7; fast electrons with energies 1-31 MeV of-0.6 to 0.8; fast neutrons -1,2 -15; slow neutrons is 1.6 to 3.8; protons 126-660 MeV - 0,5 - 1; alpha-particles and recoil Li7[B10(n, a)Li7] - 1,3-3,5; heavy particles-1-2.

Fluctuations in the values ToRBE depend on the level of radiation doses, in which these values are defined; the specific differences irradiated living organisms; the criteria used to study the action of radiation; the timing, which makes assessment of biological effects (immediate or remote); the nature of radiation (acute or chronic); peculiarities of the dose distribution in time (intensive, extended, single or fractional irradiation). The dependence of the coefficients RBE from let shown. The dependence of the coefficients RBE from the average density of ionization and let rekomendovana the International Committee on radiological protection (ICRP) for the calculation protection, presented in the table.

RBE Average specific ionization (the number of pairs of ions on 1 micron in water) The average specific energy loss in water (Kev/MK)
Up to 1
1-2
2-5
5-10
10-20
Up to 100
100-200
200-650
650-1500
1500-5000
Up to 3.5
3,5-7
7-23
23-53
53-175

Now it is accepted to use the definition of a RBE in comparative surveys of action of different types of radiation only in radiobiology. Given the variability of the coefficients RBE depending on certain conditions, for the practice of radiation protection proposed clarifying factors: the quality factor (FC) radiation and factor allocation (FR). FC characterizes the type of radiation and is associated with let the following dependence:

Let (Kev at MC in the water) FC
3, 5 and below
3,5 - 7
7 - 23
23 - 53
53-175
1
1 - 2
2 - 5
5-10
10-20

Figure FR is used to characterize the uneven distribution of radioactive isotopes on the authorities. To determine the equivalent dose of any type of radiation absorbed dose multiplied by qualifying ratios: Te= DF·[FC]·[FR]. Recommended by the ICRP be replaced for the purposes of radiation protection factor RBE quality factor (FC)that is not associated with biological parameters, but only takes into account the features of mode. Cm. also ionizing Radiation.