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
What types of DNA changes can occur?
- Changes in genetically sensitive information
- Changes in structural protein synthesis
- Changes in enzyme structure and function and enzyme substrate
What is the difference between single strand and double strand breaks?
Single Strand breaks - When only one strand is damaged, the other strand can be used as a template to guide the correction of the damaged strand - repair
Double strand breaks - hard to repair and often result in cell death
Explain indirect damage to DNA
INDIRECT damage:
- 70%-75% of total damage
- Radiolysis of water (in cells) - release of toxic free radicals
Explain Somatic Stochastic Effect
- ‘Somatic’ = body cells
- Probability of the change occurring (not severity) of which, is greater for a higher radiation dose
- No safe dose (= no threshold)
- Therefore, every exposure has the possibility of producing a stochastic effect
- Cancer
Explain Genetic Stochastic Effect
- Reproductive organs
- Damage to gonad / reproductive cells can result in congenital abnormality of the offspring
- No safe threshold
- Risk of inducing a heritable mutation is estimated to be about 2 in 100,000 per mSv
Explain Non-stochastic / Deterministic Effect
- Somatic tissues
- Severity of the change is proportional to dose
- There is a threshold dose below which no effect is seen
- Biological Changes: loss of somatic function (> 1Gy - not seen in dental)
- Xerostomia, loss of taste, skin reddening, hair loss, cataract formation
- Severe = death
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.
What is the ALARA principle?
As low as reasonably achievable
Principle of radioprotection stating that whenever ionizing radiation has to be applied to humans, animals or materials exposure should be as low as reasonably or diagnostically achievable / practicable / acceptable . It is fundamental to the principles of radiation protection.
How can you minimise the exposure for the patient?
- Only take radiographs when necessary
- Adequate filtration
- Well-maintained equipment
- Adequate collimation
- Constant potential rectification
- Lead apron and thyroid shield *
- Fastest film or intensifying screens (in Analogue system)
- Use digital imaging
- Minimize technical errors
How can you minimise exposure for the staff?
- Avoid the primary beam
- Increase Distance (inverse square law), at least 2m
- Shielding
- Position
- Most of the measures already mentioned to protect the patient
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
