Principles of Radiobiology Flashcards
1
Q
what is radiation biology?
A
Branch of biology concerned with the effects of ionizing radiation on living systems
2
Q
what are the 3 things encompassed by radiation biology?
A
- Sequence of events occurring after the absorption of energy from ionizing radiation
- Action of the living system to make up for the consequences of this energy assimilation
- Injury to the living system that may be produced
3
Q
Tissue and radiation interactions?
A
- a probability
- damage may or may not result
- 90% of interactions are harmless
4
Q
visible damage to tissue due to radiation?
A
- Indistinguishable from other causes (ie. Smoking, chemicals, etc.)
- Damage that we see may occur after a latent period of time (some time later)
- Latent period duration decreases as dose increases
5
Q
what is ionizing radiation?
A
- Damages living systems by ionizing the atoms comprising the molecular structure of these systems
- Biologic damage begins with the ionization produced by various types of radiation such as: X-rays, Gamma rays and Alpha particles
- Ionized atoms will not bond properly in molecules.
6
Q
charge, mass and energy of radiation
A
- vary among the different types of radiation
- these attributed determine the extent to which different radiation modalities transfer energy into biological tissue
7
Q
what are the three ways ionizing radiation causes injury
A
- Linear energy transfer (LET)
- Relative biologic effectiveness (RBE)
- Oxygen enhancement ratio (OER)
8
Q
what is a determinant?
A
a factor that affects the outcome
9
Q
what is Linear energy transfer?
A
- the average energy deposited as ionizing radiation passes through a medium
- described in units of keV/micron
- is a very important factor in assessing potential tissue and organ damage from exposure to ionizing radiation
10
Q
what happens to the probability of producing a significant biological response when LET increases?
A
probability also increases
11
Q
what are the radiation categories according to LET?
A
- low-linear energy transfer radiation
- high-linear energy transfer radiation
12
Q
which ionizing particles have the highest LET? the lowest?
A
alpha particles have the highest LET, followed by beta, and lastly X-ray has the lowest LET
13
Q
EMR
A
- produce electrons
- low LET
14
Q
particulate radiations
A
- can be high mass, and/or high charge
- higher LET
15
Q
Low LET
A
- quite penetrating
- sparsely ionizing
- random interactions along the length of its track - spread out - few ionizations/distance travelled
- most damage to the cell through an indirect action
16
Q
High LET
A
- less penetrating
- dense ionizations
- transfers a large amount of energy into a small area - many ionizations/distance travelled
- harder for the body to heal as there is a lot of damage in a small area
17
Q
High LET radiation damage
A
- particles possess substantial mass and charge
- can produce dense ionizations along its path and is therefor more likely to interact significantly with biological tissue
18
Q
What is Relative biologic effectiveness?
A
a measure of the damage that will occur in comparison with x-rays for the same radiation dose
– high LET radiation will have high RBE
19
Q
what is radiation weighing factor?
A
- More practical for radiation protection dose levels in humans
- Used to calculate the equivalent dose (EqD) - Determines the ability of a dose of any kind of ionizing radiation to cause biological damage
20
Q
what is the oxygen enhancement ratio?
A
the ratio of the radiation dose needed to cause the same biological damage when there is oxygen absent to when there is oxygen present
21
Q
cell radiosensitivity
A
- Equal doses of ionizing radiation produce different degrees of damage in different kinds of human cells because of differences in cell radiosensitivity.
- The more mature and specialized in performing functions a cell is, the less sensitive it is to radiation.
22
Q
what is the law of bergonie and tribondeau?
A
radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation
23
Q
the most radiosensitive cells are
A
- immature (early stages of its life cycle)
- unspecialized (undifferentiated) (not yet formed into a specific/certain tissue type)
- high reproductive activity (rate at which the cell is multiplying and dividing, more rapid more sensitive)
24
Q
what are radioinsensitive cells?
A
least sensitive to radiation
- brain cells
- muscle cells
- nerve cells
25
radio sensitivity with age?
varies with age
- very young and very old are more sensitive to radiation
26
what does the suffix blast mean?
immature, still in development, not fully specialized, rapidly dividing/multiplying
26
what does the suffix cyte mean?
mature, fully developed, specialized, not rapidly dividing/multiplying
27
stem cell versus differentiated cells?
stem cells/precursor cells/undifferentiated have much higher sensitivity to radiation that differentiated/functional cells
28
LET and cell radiosenistivity?
- The amount of radiation energy transferred to biologic tissue plays a major role in determining the amount of biologic response
- As LET increases, the ability of the radiation to cause biologic effects also generally increases until it reaches a maximal value.
- LET can influence cell radiosensitivity.
29
OER and Cell radiosensitivty?
Oxygen enhancement effects
- Oxygen enhances the effects of ionizing radiation on biologic tissue by increasing tissue radiosensitivity.
- During diagnostic imaging procedures, fully oxygenated human tissues are exposed to x-radiation or gamma radiation.
- In radiotherapy, when radiation is used to treat certain types of cancerous tumors, high-pressure (hyperbaric) oxygen has sometimes been used in conjunction with it to increase tumor radiosensitivity - may increase the amount of oxygen in cancer cells, which may make them easier to kill with radiation therapy and chemotherapy
30
Target theory?
- master, or key, molecule that maintains normal cell function is believed to be present in every cell
- master, or key, molecule is necessary for the survival of the cell
- target theory may be used to explain cell death and nonfatal cell abnormalities caused by exposure to radiation
31
What are the 2 different classifications of ionizing radiation interaction on a cell?
direct action - (DNA)
indirect action - (H2O)
- essentially the majority of effects of irradiation in living cells result from indirect action, because the human body is composed of 80% water and less than 1% DNA
32
Radiolysis of water
- dissociation of water due to ionization (splitting apart and reforming)
- ionization of water molecules
- increases effective target size
- think of skeet shooting with a .22 versus shotgun
33
what are the ways water molecules can be ionized?
- free radicals
- undesirable chemical reactions and biological damage
- cell-damaging substances
- organic free radical formation
34
what does lysis mean?
breakdown
35
what is an ion pair?
HOH+ and e-
HOH+ on its own is unstable
36
HOH+ from unstable to stable
HOH+ + e- = H2O - Positively charged water molecule may recombine with the electron
Stable molecule (water)
No damage will occur
- often happens
37
what happens is HOH+ does not recombine with an electron?
break apart into smaller molecules
decomposes into:
- H+ hydrogen ion
- OH* (hydroxyl radical)
38
what is the hydroxyl radical?
- free radical
- molecule with an uneven number of electrons (unpaired valance electrons)
- very reactive
39
what happens if the free e- combines with another water molecule?
Negative water ion
H2O + e- = HOH-
40
what does HOH- decompose into?
OH- (hydroxyl ion)
H* (hydrogen radical)
41
what is the hydrogen radical?
- free radical
- molecule with an uneven number of electrons (unpaired valance electrons)
- very reactive
42
interaction of radiation with water?
formation of:
- Ion pair (H+ and OH-)
- Hydrogen ion and a hydroxyl ion
- Two free radicals (H* and OH*)
- Hydrogen radical and a hydroxyl radical
43
what happens if the H* and OH* bond?
H* and OH*
OH* could bond with another OH*
OH* + OH* = H2O2 (hydrogen peroxide)
Poisonous to the cell
HO2* hydroperoxyl radical
H* + O2 = HO2*
The two are believed to cause the most damage
44
what are free radicals?
Uncharged molecule
Reactive
Diffusible
45
