Radiobiology Flashcards
When an individual takes any x-ray, what method should always be practiced, and what does that method stand for?
- ALARA
- As Low As Reasonably Achievable
T/F: For the patients protection, the doctors should minimize time, maximize distance, shield the patient, filter the x-ray tube, and establish the patients ability to understand and cooperate during imaging,
TRUE
In order to limit x-ray exposure the tube has to be ____ to the smallest field size of the desired anatomy.
collimated
T/F: Only order and perform radiographic study as determined by medical necessity.
True
Understand the importance of _____ examination and differential diagnosis before ordering the study.
physical examination
T/F: Radiography could be used in place of physical examination
FALSE!
Who are the most vulnerable patients to radiographic study?
Pregnant women and children
When is full body shielding used?
Extremity imaging
When is partial shielding used?
Cervical and thoracic spine radiography
When is gonadal shielding used?
Patients that are either…
- Patients of reproductive age
- Children
What view is better for radiation exposure in the thoracic area PA or AP?
PA
What does the 1906 Law of Bergonie and Tribondeau state?
Radiosensitivity of cells is dependent on their rate of maturation or differentiation and metabolism
What cells in your body are the most sensitive to radiographic imaging…
- Stem cells
- young cells
- Cells with higher rate of mitosis (ex. enterocytes, skin cells)
In imaging young children, where should the partial shielding, specifically on the gonads, be placed on the children.
Male - lower on the testicles (as they hang lower)
Female - higher to cover the ovaries
How is radiation measured?
Physical factors influencing radiosensitivity. It is estimated by the amount of energy absorbed per unit mass or (Rad)
T/F: The same radiation amount irradiating (exposure to radiation) the same mass unit may produce different tissue damage
TRUE
What is the Linear Energy Transfer (LET)? What does this measure?
- This measures the rate with which energy is transferred from ionizing radiation to soft tissues.
- The LET is another method of expressing radiation quality and determining the value of radiation weighting factor, this reflects the different amount of potential biological effect for each type of radiation source (ex. x-rays, gamma rays, b-particles or a-particles)
T/F: The ability of ionizing radiation to produce biologic response increases as the linear Energy Transfer of radiation decreases.
FALSE: The ability of ionizing radiation to to produce biologic response increases as the LET of radiation increases
What are the 3 biologic factors affecting radiosensitivity?
- Age
- Oxygen effect
- Recovery
How is the oxygen effect a biological factor affecting radiosensitivity?
- Tissues are more radiosensitive when irradiated under oxygenated state
- Hypoxic or anoxic tissues are less radiosensitive
How is Age a biological factor that affects radiosensitivity?
- Humans are more radiosensitive before birth (3-7 weeks of fetal life)
- After birth radiosensitivity decreases and reaches its lowest point after maturity (tissues are better at repairing themselves)
- In old age radiosensitivity is increasing slightly (cells are old, and not as good at repair)
How is Recovery a biological factor affecting radiosensitivity?
- If the radiation is not sufficient to kill the cell, biochemically the cell will be able to recover
- Some cells may die which will cause organ atrophy. The surviving cells will eventually repopulate the damaged tissue
T/F: Tissues are less radiosensitive when irradiated under oxygenated state. Hypoxic or anoxic tissues are more radiosensitive
- FALSE:
- Tissues are more radiosensitive when irradiated under oxygenated state
- Hypoxic or anoxic tissues are less radiosensitive
T/F: If the radiation is not sufficient to kill the cell, the cells biochemical machinery may recover. Some cells may die causing organ atrophy. The surviving cells will eventually repopulate the damaged tissue.
TRUE
A chemical agent is considered what?
- Radiosensitizers
- Radioprotectors
What does a radiosensitizing chemical agent do?
- Some agents such as halogenated pyrimidines, vitamin K and methotrexate are capable of enhancing radiosensitivity.
- Which means that if 90% of a cell is destroyed, for example, 200 rad, then by administering these chemical agents will require only 100 rad to produce a lethal dose.
- Basically these agents make a dose super lethal when it shouldn’t be, like 100 rad shouldn’t at all be dangerous to the patient, but if they are on Vit K or methotrexate, the 100 rad dose will become lethal).
What does a radioprotective chemical agent do?
- Theoretically agents such as sulfhydrils (sulfur + hydrogen), ex. cysteine, may lessen cell radiosensitivity
When H2O is irradiated it dissociates into free radicals (H2O2, hydroxil radicals etc). This is known as ______ of water.
Radiolysis
Living cells are composed of approx. ___% of H2O.
- 80%
- Thus irradiation of H2O represents principle effects of ionizing radiation
In dealing with the biological effects of radiation, what does ionization produce?
Free radicals
Define target theory…
- DNA- is the target
- The target theory indicates that in general most cells contain overabundance of different molecules
In the target theory what is classified as a direct effect?
- DNA molecule is the smallest in a cell
- Thus it will become a target molecule for x-rays
- This is the direct effect
In the target theory what is classified as the indirect effect?
- When x-rays hit H2O which will then release an ion radical
- This will then “hit” DNA indirectly
List these in order of increasing sensitivity to radiation.
- Lymphocytes
- Epithelial cells
- Endothelial cells
- Bone cells
- Brain cells
- Muscle cells
- Erythrocytes, Granulocytes
- Connective Tissue cells
- Nerve cells
Most: 1 7 2 3 8 4 9 5 6 Least
Radiosensitivity of various cell types…
Name High, Intermediate, Low…
Low: Nerve, Muscle
Intermediate: Osteoblast, endothelial cells, fibroblast, spermatids
High: Spermatogonia, lymphocytes, stem cells, intestinal mucosa cells, erythroblast
T/F: According to the dose response relationship, the linear dose-response is directly proportional to radiation dose
TRUE
In the dose-response relationship, every radiation dose-response has two characteristics, what are they?
Linear and Non-Linear
T/F: According to the dose response relationship the Non-Linear dose-response is also called non-threshold type, which means that any dose, regardless its size will produce a response
FALSE
- According to the dose response relationship the non-linear response or threshold response describes anything below that dose threshold the radiation affects are less significant.
If the dose is above the threshold this will often relates to killing of the cell
What dose response relationship will cause radiation induced cancer, leukemia, and genetic mutations which assumes, NO PHOTON IS SAFE.
Non-threshold (linear) type
In diagnostic radiography which dose response predominates?
Linear dose-response (non-threshold type)
T/F: For establishing the safety guidelines in radiography, a linear threshold response is applied.
FALSE
- For establishing the safety guidelines in radiography, a linear non-threshold response is applied
T/F: Non-linear Dose-Response means varied doses may produce varied responses. This may also mean that there is a threshold dose below which there is no response.
TRUE
T/F: When only part of the body is irradiated, higher doses can be tolerated.
TRUE
The ____ effect refers to most immediate radiation related tissue damage with a threshold above which the severity of damage is related to dose.
Deterministic
Dose-Response Curves Image.. Look up an image
- Linear - response is directly related to the dose
- Non-Linear - the response is not proportionate to the dose
- Threshold - the dose at which effects are produced; below this dose, there are no obvious effects
- Non- threshold - any dose produces a response
What does the deterministic effect lead to?
Cell killing
Acute radiation sickness/syndrome with hematologic death, GI tissue death, and severe CNS death and coma are good examples of what?
Dose related - i.e. Threshold
Deterministic effect occurs when?
When the effects of large doses of radiation are certain to occur because the dose EXCEEDS a THRESHOLD level
The ____ effect is expressed by cancerogenesis, mutations and hereditary changes…
Stochastic
T/F: The stochastic effect is a threshold effect of ionizing radiation.
FALSE
- The stochastic effect is a non-threshold effect of ionizing radiation
What would be considered the best example of stochastic effect?
- Latent cancer developed in people who were exposed to radiation sometimes 20-30 years PRIOR
The period of _____ which is how may weeks of fetal life, is most susceptible to radiation effects due to the high metabolic and high growth rate of the cells with in the fetus?
- Organogenesis, 3-7 weeks
_____ measures radiation exposure or intensity detectable in the air.
Roentgen
Ionizing radiation imaging of children must be exercised with great caution due to their longer life after the exposure and what type of dose response to radiation?
- Linear-dose response
- Select non-ionizing radiation imaging whenever possible, diagnostic ultrasound and MRI preferred
What is a “RAD” and what is the lethal dose?
RAD - measures how much energy is absorbed per unit mass. 350 RADs - Human lethal dose (LD) (50%-DIE WITHIN 60 DAYS)
T/F: Dose vs. Cell recover time are directly related
FALSE
- Dose vs. Cell recovery time are inversely related
Currently the (System internationale) preferred unit is: 1 ___ which equals 100 RADs.
Grey
What does REM stand for and what is it used for?
- Radiation equivalent mammals/man
- It is used as a unit of radiation exposure measuring potential biological effects
- This determines the difference of biologic effectiveness between different radiation sources: For example: x-rays, gamma-rays may have the same effect
Alfa-particle radiation can cause damage ___ times greater…
20
Most radiography stuff receives approx. ___ mSv/yr or less…
0.5
T/F: Sievert (Sv) is the used measure: 1Sv=100Rem
TRUE
What are the sources of Radiation exposure from greatest to least?
Radon: 55% Diagnostic X-rays: 11% Internal: 11% Terrestrial: 8% Cosmic: 7% Nuclear Medicine: 4% Consumer Products: 1%
Radiation units…
Roentgen: A unit for measuring the amount of gamma or X rays in air
Rad: A unit for measuring absorbed energy from radiation
Rem: A unit for measuring biological damage from radiation
What is hormesis?
In the last several decades there is growing evidence suggesting that experimental animals who receive low radiation dose express better survival ability
