A biologic reaction is produced by 4 Gyt of a test radiation. It takes 16 Gyt of 250-kVp x-rays to produce the same biologic reaction. What is the relative biologic effectiveness (RBE) of the test radiation?
4
While passing through a human cell, an x-ray photon interacts with and inactivates the cell's master molecule. What is the consequence for the cell?
Death
Which of the following curves illustrates the radiation sensitivity of a particular type of cell?
Survival Curve
Which of the following groups of cells is least radiosensitive?
-Adult nerve cells
-Nerve cells in an embryo or fetus
-Lymphocytes
-Immature spermatogonia
Adult Nerve Cells
OH
+ OH
= __________.
H2O2
Which of the following gonadal radiation doses may cause permanent sterility in a male human?
6 Gyt
Which of the following groups of cells is most radiosensitive?
Lymphocytes
Direct action may occur after exposure to any type of radiation, but it is much more likely to happen after exposure to:
High LET radiation such as Alpha particles
The radiosensitivity of ova:
varies considerably throughout the lifetime of the germ cell.
If bone marrow cells have not been destroyed by exposure to ionizing radiation, they can:
Repopulate after a period of recovery
Biologic damage begins with ionization and following the ionized atom does not:
bond properly in molecules/ recombine
List the 3 Radiation Energy Transfer Determinants
1) LET (Linear energy transfer)
2.) RBE (Relative biologic effectiveness
3.) OER (Oxygen enhancement ratio
L.E.T
Linear energy transfer
R.B.E
Relative biologic effectiveness
O.E.R
Oxygen enhancement ratio
The average energy deposited per unite length of track defines:
LET
Units for previous radiation energy transfer determinant is:
KeV/�m
When LET ______, the chance to produce significant biologic response in the DNA macro molecule _____.
Increases, increases
What type of radiation is generally considered Low LET?
X-rays and gamma rays
Low LET radiation causes damage primarily through:
indirection action
What are free radicals?
Solitary atoms that are very chemically reactive single entities
Lower LET radiation generally causes _____ damage to the DNA, but ______ can usually revers the cellular damage
sub-lethal, repair enzymes
What type of radiation is generally considered high LET radiation?
Alpha, Ions of heavy particles, Low energy neutrons
High LET radiation includes particles that possess substantial ____ & ____
Mass & charge
High LET _____ energy more rapidly than ___ LET b/c they produce much more ______ per unite of distance traveled.
Lose, low, ionization
What holds high probability of interactions with DNA?
High LET
Compton scattered electrons or photoelectrons may interact with ____ of cells with low probability of changing the ____.
Thousand, DNA
Alpha cells will travel through ______ cells, with _____ probability of interacting with the cell DNA.
1-2 cells, high
High LET is greatest concern with
internal contamination
Low LET have _____ damage, while high LET have _____ damage.
Indirect/ repairable, Direct/ irreparable
Relative Biologic Effectiveness describes:
the relative capabilities of radiation with differing LETs to produce a particular biologic reaction
Formula for RBE:
RBE= Dose in Gy from 250 kvp of x-rays/ dose in Gy of test radiation
WR (Radiation weighting) values
similar to the values of RBE for any particular type of radiation
What makes biologic tissue more sensitive to radiation?
When it is irradiated in an oxygenated or aerobic state
Oxygen enhance ratio
ratio of the radiation dose required to cause a particular biologic response of cell or organism in an oxygen deprived environment to the radiation dose required to cause an identical response under normal oxygenated conditions.
OER of High LET
1 OER
OER of Low LET
3 OER
X-rays and gamma rays have OER of
3 OER
What causes permanent/ fixed/ lethal damage?
Damage produced by a free radical in the presence of oxygen, because the free radicals rejoin to produce organic peroxide compounds.
Alpha particles and High LET have OER of
1 OER
Free Radicals
solitary atom or combination of atoms acts as an extremely reactive single entity as a result of the presence of an unpaired electon
Radiation to a germ cell causes damage that maybe passed on to
future generations in form of a genetic mutation
Direct action
when biologic damage occurs as a result of ionization of atoms on essential molecules, potentially causing these molecules to become inactive or functionally altered
Radiolysis of water
when effects of radiation are produced by free radicals that are created by the interaction of radiation with water molecules
With radiolysis of water, _____ of all radiation induced damage is believed to be ultimately cause by the ___
2/3, OH*
What is H2O2?
hydrogen peroxide- cell damaging/ killing
HO2?
Hydrogen free radical (H*) combines with molecular oxygen (O?)
H2O2 & HO2 produce biologic damage:
directly after the interaction of radiation with water
Human body is _____ water and _____ DNA, thus all effects of irradiation in living cells result from _________.
80%, 1%, indirect action