Radiation Safety Flashcards
If a patient interacts with x-ray photons what are the 3 possible outcomes?
- X-ray photons pass through patient without any interaction
- X-ray photons are completely absorbed by patient
- X-ray photons are scattered (coherent and incoherent)
How are black and white images produced?
The photons that get absorbed = white image
The photons that pass through = black image
What happens if a photon has no interaction with a tissue?
X-ray photon passes through atom unchanged
- These photons contact the film emulsion or receptor to produce an area of darker density
- ~9% of the primary photons
As the x-ray beam passes through tissues, photons get absorbed or scattered by the tissues, resulting in decreased energy of the beam
True
What is beam attenuation?
Reduction of the x-ray beam intensity as it passes through tissues
In dental x-ray beam, what are the 3 means of beam attenuation?
1) Photoelectric absorption (~27%)
2) Thompson/Coherent scattering (~7%)
3) Compton/Incoherent scattering (~57% of the primary beam)
What is 1 day of background radiation equivalent to?
~0.005mSv
What is the absorbed dose?
•Absorbed dose: radiation (in Joules) received by patient (in kg)
What is the equivalent dose?
Equivalent dose = radiation absorbed by an organ
- It is used to compare biologic effects of radiation on different types of tissue or organ
- Unit is the Sievert (Sv)
What is the effective dose?
Effective dose = radiation absorbed by an organ, affecting the entire body
Effective dose = equivalent dose x tissue weighting factors (WT)
Tissues are grouped into:
- high risk (WT = 0.12),
- moderate risk (WT = 0.4-0.8) &
- low risk (WT = 0.01)
Example: 100mSv to skin (= low risk tissue, WT = 0.01) = 1mSv to body
It is used to estimate the risk in humans
Unit is the Sievert (Sv)
Which cells are more radiosensitive?
- Cells with a high mitotic activity
- Cells with a high metabolic activity
- Pluripotential (primitive) cells
- Eg. Children
What is the allowable annual dose limits in Dentistry (effective dosage) for the public?
1mSv / year (averaged over 5 years)
Special clause: Can exceed in special circumstances (eg. Radiotherapy) as long as it is 1mSv averaged over 5
What is the annual dose limit for dental workers?
20mSv / year (averaged over 5 years)
- No more than 50mSv in any one year
- If under 18 but over 16, limit is 6 mSv per year
What are the outcomes of ionising radiation on cells?
- It may pass directly through the cell without causing any damage
- It may interact with cells and cause DAMAGE - Cells can either:
a) Repair itself
b) Mutate, or
c) Die
Explain direct damage
Damage to cell walls, mitochondria, mRNA, nuclear membrane, DNA, etc.
DIRECT damage:
- 25%-30% of total damage
- Direct damage to atoms / molecules eg. DNA
When an atom becomes ionized, it become unstable = free radicals, which are highly reactive and short-lived
Free radicals then quickly stabilize by dissociation (breaking apart) or cross-linking
Structurally and functionally different molecules and a consequent biologic change
Explain indirect damage to DNA
INDIRECT damage:
- 70%-75% of total damage
- Radiolysis of water (in cells) - release of toxic free radicals
Compare Stochastic and Deterministic Effects
Explain cumulative effect of an xray
There is evidence that dose accumulated over a long period carries less risk than the same dose received over a short period.
This applies to radiotherapy. Typically, 2 Gy is delivered daily for a weekly exposure of 10 Gy. The radiotherapy course continues for 6 to 7 weeks until a total of 60 to 70 Gy is administered.
Can you take xrays in pregnancy?
Probability of Child’s Death from Diagnostic X-ray (dental or medical) VS. Probability of Child’s Death from Maternal Smoking
10 x annual patient radiation dose <<<<< 1 cig/day maternal smoking
Ideally take them 2nd trimester with lead apron
