7 Radiation biophysics, dosimetry, biological effect of radiations Flashcards
What is the biological effect of radioactive radiation based on?
Excitation and ionization of atoms and/or molecules of living systems.
How does the number of ionizations depend on the dose of the radiation?
The number of ionizations is linearly proportional to the dose.
What is D37?
D37 denotes the dose at which 37 % of the irradiated objects survive. If one ionization causes inactivation, D37 corresponds to one hit in a radiosensitive volume (VD=1, that is D=1/V).
What is a hit in radiation biology?
If one or more ionizations are produced in the radiosensitive volume of a biological object.
How can a dose-response curve be constructed?
The applied radiation dose is plotted on the horizontal axis and the ratio of the surviving organisms (N) and the total number of organisms before irradiation (N0) is plotted on the vertical axis.
What is the principle of the indirect action of radiation?
In aqueous solutions a particle of an ionizing radiation most probably causes ionization of the solvent (water) because water molecules outnumber solute molecules. Radicals generated by the above process are responsible for damaging solute molecules. This way the target “gets bigger”.
What kind of products are capable of damaging biological objects arise during irradiation of aqueous solutions?
hydrated e–, H, OH, H2O2
What is the definition of absorbed dose?
Absorbed dose, Da, is defined for any ionizing radiation as the ratio of radiation energy converted into ionization energy and the mass taking up the ionization energy. Unit: Gray (Gy), 1 Gy= 1J/kg
What is the definition of absorbed dose?
Absorbed dose, Da, is defined for any ionizing radiation as the ratio of radiation energy converted into ionization energy and the mass taking up the ionization energy. Unit: Gray (Gy), 1 Gy= 1J/kg
Define the unit of equivalent dose!
Its unit is 1 Sievert (Sv). 1 Sv is the dose of any ionizing radiation which produces the same effect on human beings as 1 Gy absorbed dose of conventional X-ray. Conventional X-ray consists of 250 keV photons.
Define effective dose. Why is it necessary to introduce effective dose when examining radiation damage in biological organisms?
Effective dose is the weighted sum of the equivalent doses in all specified tissues and organs of the human body (or other biological organism). It should be used because the extent of radiation damage is influenced by the radiation sensitivity of the irradiated tissues/organs as well. When the effective dose is calculated, differential radiation sensitivities of tissues/organs are taken into account using tissue -specific weight factors.
List the physical factors influencing radiation sensitivity!
The quality of radiation (it influences radiation sensitivity through ionization density and penetrability), time factor, temperature, effect of oxygen, substances protecting from radiation.
What is the smallest dose which can produce a biological effect?
Theoretically even a single quantum is enough to produce a point mutation, since any photon that is able to produce ionization is capable of breaking a chemical bond.
How can radioactive radiation cause a double strand break in DNA?
A double strand break of DNA can be caused by a single ionization event or as a result of simultaneous single strand breaks on the opposite strands of DNA helix which are produced by ionizations originating from separate events.
In which part of the cell cycle are cells the most and the least sensitive to radioactive radiation?
Generally, the majority of cells are considered to be the most radiosensitive during mitosis and most resistant in late S phase.
