Principles of radiation biology Flashcards
1
Q
What is radiation biology?
A
The branch of biology concerend with the effects of ionizing radiation on living systems
2
Q
What are these three things describing?
- The sequence of events occuring afger the absorption of energy from ionizing radiation
- The action of the living system to make up for the consequences of this energy assimilation
- Injury to the living system that may be produced
A
Radiation biology
3
Q
At what level does potentially harmful effects of ionizing radiation primarily occur at?
A
The cellular level
4
Q
What percentage of interaction of ionzing radiation with tissues are harmless?
A
90% of interactions are harmless
5
Q
T/F
Interactions are a probablilty and may or may not result in damage
A
True
6
Q
T/F
The latent period duration of visible damage decreeases as dose increases.
A
True (the larger the radiation dose the quicker the reaction)
7
Q
T/F
Visible damage from radiation is indistinguishable from other causes.
A
True
8
Q
T/F
It is difficult to determine if low (diagnostic) levels of radiation cause damage
A
True
9
Q
How does ionizing radiation damage living systems?
A
By ionizing the atoms comprimising the molecular structure of these systems
10
Q
T/F
Ionzied atoms can bond properly with molecules provided that a low LET reaction occured.
A
False; ionzied atoms will not bond properly in molecules
11
Q
What does LET stand for?
A
Linear energy transfer
12
Q
What does RBE stand for?
A
Relative biologic effectivness
13
Q
What does OER stand for?
A
Oxygen enhancement ratio
14
Q
What attributes determine the extent to which different radiation modalilties transfer energy into biologic tissue?
A
Charge, mass and energy
15
Q
What are the three concepts that help us to understand the way ionizing radiation causes injury and how the effects may vary in biologic tisssue?
A
- LET
- RBE
- OER
16
Q
What is the defenition of LET?
A
The average energy depositied as ionizing radiation passes through a medium (per unit lenth of track)
17
Q
What are the units for LET?
A
keV/um (kiloelectron volts per micron)
18
Q
T/F
An increased LET increases the chances of producing a significant biological response.
A
True
19
Q
What are the two categories of LET?
A
- Low linear energy transfer radiation
- High linear energy transfer raidation
20
Q
What type of LET is harder for the body to repair? Why?
A
High lET; becuase the there are more ionziations
21
Q
What does LET allow us to asses?
A
The potential tissue and organ damage from exposure to ionzing radiation
22
Q
T/F
When E deposits are spread out more, the body is able to fix them eaiser.
A
True
23
Q
What types of radiation are labled 1-3?
A
- Alpha radiation
- Beta radiation
- X-ray radiation
24
Q
What types of radiation are considered low LET radiation?
A
- Gamma rays
- X-rays
25
**What types of radiation are considered high LET radiation?**
1. Particulate radiation (alpha, neutrons)
26
# T/F
**EMR is considered low LET**
True
27
**What is the general mass (high or low) and charge (+/-) of low LET radiation?**
-Low mass
-Negative charge
28
What is the general mass (high or low) and charge (+/-) of high LET radiation?
-High mass and/or;
-High charge
29
What is the penetrating ability of low LET radiation?
Highly penetrating
30
What type of action is responsible for most damage that occurs to the cell with low LET radiation?
Indirect action
31
# T/F
With low LET raidation, ionziations are very frequent.
False; low LET radiation is sparsely ionzing
32
What do the interactions with tissue look like for low LET radiation?
-Interactions (ionziations) spread out along the length of the tissue track
-Few ionziations over the distance that it traveled
33
What is the penetrating ability of high LET radiation?
Less penetrating than low LET radiation
34
What do the interactions with tissue look like for high LET radiation?
-Transferes a large amount of ionizations over a small area of tissue
35
What are the chances of low LET radiation damging the structure of the DNA? What is this interaction called?
-Very low
-It is called a direct hit
36
If low LET radiation does cause a direct hit, it this reparable or unreparable?
Reparable
37
Why are direct hits to DNA less common with low LET radiation?
There is a higher chance it will miss the DNA because the ionziations are spread out
38
# T/F
With high LET, there as more of a chance for a direct hit to the DNA
True
39
What is the defenition of RBE?
The relative capabilites of radiation with differing LETs to produce a particular biologic reaction
40
**How do you calculate RBE?**
RBE=Dose of standard radiation necessary to produce a given effect **OR** dose in Gy from 250 keV x rays/dose of *test* radiation necessary to produce the same effect
41
**What is the typical amount of reference necessary to produce a given effect?**
| (for the RBE calculation)
Conventionally 250 kVp x rays
42
What does WR stand for?
The radiation weighing factor
43
What is the WR for x-rays?
1
44
What is the WR for alpha radiation?
20
45
What is the purpose of the Raidaiton weighing factor?
-It is more practical for radiation protection dose levels in humans as it is used to calculate the EqD
46
What does EqD determine?
Determines the ability of a dose of any kind of ionizng radiation to cause biological damage
47
# T/F
Tissues in an oxygenated state are more sensitive to radiation
True
48
**How do you calculate the OER?**
OER=Radiation dose required to cause biologic response without O2/Radiation dose required to cause biologic response with O2
49
# T/F
High LET radiation will have a high RBE
True
50
# T/F
OER is the measure of the damage that will ocur in comparison with the x rays for the same radiation dose.
False; **RBE** is the measure of the damage that will ocur in comparison with the x rays for the same radiation dose.
51
# T/F
OER is the ratio fo the radiation dose needed to cause the same biological damage when there is oxygen absent to when there is oxygen present.
True
52
Why is it that equal doses of ionzing radiation produce different degrees of damge in different kinds of human cells?
It is because of the differences in cell radiosensitivity
53
# T/F
**The more mature and specialized in performing functions a cell is, the less sensitive it is to radiation**
True
54
# What law is this describing?
Radiosensitivity of cells is directly proportional to thier repoructive activity and inversely proportional to their degree of differentiation.
The law of Bergonie and Tribondeua
55
What 3 cells of the body are more radioinsensitive?
1. Brain cells
2. Muscle cells
3. Nerve cells
56
Name three cells of the body that are more radiosensitive:
1. Reproductive (germ) cellls
2. Basal cells of the skin
3. Intestinal crypt cells
57
Why is there an increase in radiosensitivity when the patient is older?
There is less healing able to take place
58
What is more sensitive to radiation, spermatogonia or spermatozona?
Spermatogonia
59
# T/F
LET can influence cell radiosensitivy
True
60
# T/F
Oxygen enchances the effects of ionzing radiation by increasin the tissue radiosensitivity.
True
61
How does radiotherapy take advantage of the oxygen enhancement effects of tissues.
In radiotherapy, high pressure oxygen has sometimes beeen used in conjunction with radiation to increase tumor radiosensitivity
62
**What is the target of the cell?**
It is the master orkey molecule that is believed to be in every cell, necessary for the survival of the cell
63
What theory can be used to explain cell death and non fatal cell abdomalities caused by exposure to radiation?
Target theory
64
# T/F
Both indirect and direct hits to a cell can cause damage.
True
65
What is the target molecule in all cells?
The DNA
66
# T/F
If a molecule misses the key molecule, no damage to the cell will occur.
True
67
What are the two classifications of ionzing radiation interaction on a cell?
1. Direct action
2. Indirect action
68
**What do the majority of effects of irradiation in living cells result from?** Why?
Indirect action, because the human body is composed of 80% water, and less than 1% DNA
69
# T/F
Indirect action increases the effective target size
True
70
Define radiolysis:
The breakdown of rater caused by radiation
71
What are the effects of the radiolysis of water?
1. Production of free radicals
2. Production of undesirable chemical raeactions and biologic damage
3. Production of cell damaging substances
4. Organic free radical formation
72
What is a free radical?
Formed by the radiolysis of water
73
What is an ion pair made up of?
HOH+ and e-
74
# T/F
HOH+ on its own is stable.
False; HOH+ on its own is unstable
75
# T/F
A positive ion on its own is unstable.
True
76
What are the different possibilities that can occur with ion pairs from the radiolysis of water?
1. Positively charged water milecule may recombine with the e-
2. Can break apart into smaller molecules
3. Free e- can combine with another water molecule
77
What reaction has to occur for an ion pair to turn from unstable to stable? Will any damage occur?
-HOH+ will recombine with the electron to form a stable water molecule.
-No damage will occur
78
If a positive does not recombine with an electron, and breaks apart into smaller molecules, what will it decompose into? Will this cause damage?
1. H+ (hydrogen ion)
2. OH (hydroxyl radical)
-Will cause damage
79
What is OH?
-It is a free radical, with an uneven # of electrons that is highly reactive
80
If a positive does not recombine with an electron, but instead, the free e- combines with another water molecule, what will this create? What will it eventually decompose into?
-Creates HOH- (Negative water ion)
-Will decompose into OH- (hydroxyl ion) and H (hydrogen radical)
81
What is H (hydrogen radical)?
It is a free radical with an uneven number of elecrons that is very reactive
82
# Summary
What are the 2 formations that can occur from the interaction of radiation with water?
1. Hydrogen ion and a hydroxyl ion (H+ and OH-)-safe
2. Two free radicals-Hydrogen radical and a hydroxyl radical (unsafe)
83
What can occur if H and OH radicals interact and **transfer energy to other molecules?**
Can break chemical bonds causing point lesions that lead to cell death
84
What is the radiolysis of water considered; direct or indirect?
Indirect action
85
What interaction can occur with free radicals other than the transfer of energy to tissues?
OH (free radical) could bond with another OH, causing the creation of hydrogen peroxide, which is poisinous to the cell
86
What free radical is considered to be the most harmful to the cell?
Hydriperoxyl radical (HO2)
87
What is the chemical equation for the interaction that occurs when an ion pair recombines?
H2O+radiation--->HOH+ + e-
88
What is the chemical equation for the interaction that occurs when an e- attaches to another water molecule?
H2O+e----> HOH-
89
What is the equation for the dissasosiation of HOH+?
HOH+--->H+ + OH
90
What is the equation for the dissasosiation of HOH-?
HOH- --->H+ + OH-
91
# T/F
Free radicals are diffusible.
True
92
What are the 3 possibilities with free radical interactions?
1. Recombination
2. Combination of free radicals
3. React with normal biologic molecules forming new or damaged structures
93
How do free radicals initiate damage?
Through indirect action
