Radiation safety Flashcards
Define radiosensitivity
Relative susceptibility of cells, tissues, organs or organisms to the harmful effect of ionizing radiation.
Describe characteristics of highly sensitive cells
Undifferentiated
Well nourished
Divide quickly
Highly active metabolically
Examples: Intestines, testes, mucous membranes, bone marrow
Describe characteristics of low sensitive cells
Differentiated
Limited supply
Divide slowly
Low active metabolically
Examples: Neurons, muscles
What is effect dose?
The Effective Dose (E) is used to estimate Radiation risk, measures the equivalent whole-body dose
What are effective dose levels for:
- A year
- Occupations
- Public
- The effective dose limit shall not exceed 50mSv in any one year
- Occupational dose 20mSv per year, averaged over a period of 5 consecutive calendar years
- Public shall not exceed 1 mSv per year
What is a direct effect of radiation?
In direct effects, biological materials absorb energy from ionizing radiation, and form unstable free radicals
Free radicals induce changes molecular changes in biological matters
As a result, the biological matter is altered from its original state
What is an indirect effect of radiation?
Most of our cellular structures are water.
When radiation reacts with water, it may break the bonds that hold the water molecule together, producing fragments such as hydrogen (H) and hydroxyls (OH).
These could combine to form toxic substances, such as hydrogen peroxide (H2O2), which can contribute to the destruction of the cell.
What is a deterministic effect of radiation?
Can be seen in very short time after exposure to radiation
Occurs when radiation exposure exceeds threshold
Severity of the effect is dose related
Occurs when too many cells are killed at once, meaning radiation doses are high
The higher the dose, the worse the effects
Examples: Radiation burns, cataracts
What is a stochastic effect of radiation?
Happen a while after exposure
No threshold to start
Severity of the effect is not dose related
Occurs when even one photon interacts with DNA, causing changes in its structure
The higher the dose, the higher the chances of getting the illness
Examples: Cancer
What is the principle of ALARA?
ALARA (As Low As Reasonably Achievable)
Justification:
The diagnostic benefit of performing the x-ray exceeds the risk of harm. The clinician should also fully understand why a radiographic examination is prescribed.
Optimization and Dose limitation:
• Dose Limitation: The dose limits for all involved must be within, or below the limits as much as possible
• Using a rectangular collimator exposes 60% less tissues to x-rays than round collimators
• Position and distance rule: stay 2m away from the x-ray emission source, and not in direct line with it.
• Inverse square law: This law accounts for the fact that the intensity of radiation becomes weaker as it spreads out from the source since it becomes spread over a larger area.
