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31 Cards in this Set

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107. What is the biological effect of radioactive radiation
based on?
Excitation and ionization of atoms and/or molecules of
living systems.
108. What kind of particles are able to produce a biological
effect?
Particles giving their energy partially or totally to the
biological object are able to produce a biological effect.
109. What is a hit in radiation biology?
If one or more ionizations are produced in the
radiosensitive volume of a biological object.
110. 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 probability of generating exactly ‘n’ hits when
applying a dose of D in volume V?
Pn=(vD)^n/n! X e^−νD
112. How does the number of ionizations depend on the dose
of the radiation?
The number of ionizations is linearly proportional to the
dose.
113. What kind of equation describes the dose-response
curve in the special case when one hit is necessary for
inactivation?
N/No=e^−νD
where N is the number of surviving organisms, No is the
total number of organisms, D is the dose and v is the
radiosensitive volume.
114. 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
(V·D=1, that is D=1/V).
115. What is D50 and D50/30?
D50 is the dose at which 50% of the objects survive,
while D50/30 is the same dose when the observation time
is 30 days.
116. 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”.
117. What kind of products capable of damaging biological
objects arise during irradiation of aqueous solutions?
hydrated e–, H•, OH•, H2O2
118. List the changes that H• and OH• radicals can produce
on the biological molecules!
MH + H• = MH2•
MH + OH• = MHOH•
MH + H• = M• + H2
MH + OH• = M• + H2O
where MH denotes a biological molecule.
119. Give the equation describing the dose-response curve if
water radicals can interact with each solute molecule
only once!
N/No=1-kD
where N is the number of surviving organisms, No is the
total number of organisms, D is the dose and k is a
constant.
120. Write down in one sentence the dilution effect in the
case of irradiation of an enzyme solution!
Upon dilution under the same irradiation conditions the
ratio of inactivated molecules increases to a certain
dilution, because the number of radicals per enzyme
molecule increases.
121. Explain briefly why the proportion of inactivated
molecules increases only until a certain degree of
dilution is reached!
Above a certain dilution the radicals are formed so far
away from the enzyme molecules that they cannot reach the target (enzyme), instead they recombine with each
other.
122. 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.
123. What is the definition and unit of KERMA (kinetic energy
released in material)?
KERMA is the sum of the initial kinetic energy of all
particles generated by the ionizing radiation in an
absorbing material divided by the mass of the absorbing
material. Unit: Gray (Gy).
124. What is the definition of exposure and its unit in the case
of X-ray and γ-radiation?
Exposure is defined as the ratio of the sum of positive
(or negative) charges produced by ionization in a volume
element and the mass of this element if every charged
particle loses its kinetic energy in air. Its unit:
Coulomb/kg.
125. 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.
Coventional X ray consists of 250 keV photons.
126. 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.
127. 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.
128. List the radioactive radiations in order of increasing
penetrability!
α<β<γ<n
129. What is the physical quantity whose unit is Gray and
how can it be defined with other SI units?
Gray is the unit of absorbed dose, 1 Gy=1 joule/kg.
130. What is transmutation?
A radioactive isotope is converted to another chemical
element through its decay (e.g. 32S is generated from
32P). This may cause a single strand break and a
mutation in DNA.
131. What are the critical molecules in a cell, the integrity of
which is essential for the survival and the reproductive
function of the cell?
Double stranded DNA.
132. What is the critical damage caused by radioactive
radiation in DNA?
The critical damage is double strand break.
133. 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.
134. Write the equation describing cell survival according to
the linear-quadratic model.
S(D) = e^−(αD+βD^2)
Where S(D) is the survival fraction as a function of dose
D, and α and β are tissue and radiation dependent
constants. Parameters α and β are proportional to the
probability of "one-step" and “two-step” DNA double
strand breaks, respectively.
135. 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.
136. How does radiosensitivity changes with different degrees
of oxygenation?
The dose-response curve of well-oxygenated cells
demonstrate a relatively narrow initial shoulder and a
steep linear portion indicating greater radiosensitivity.
Hypoxic cells show a wide shoulder and a less steep
linear portion of the survival curve indicating increased
radiation resistance.
137. How and why does fractionation of radioactive radiation
influence the radiosensitivity of cells?
Fractionation decreases the radiosensitivity of cells,
because radiation-induced damage can be partly
repaired between exposures to the radiation.