Radiology 5 Flashcards
Two biological effects of radiation
Deterministic and non-deterministic
Deterministic
Non-stochastic: those we know will occur.
Threshold dose (known)
Somatic effects.
Non-deterministic
Stochastic: those which may occur.
Down to chance, no threshold (unknown).
How can somatic effects be used clinically
Patient treated for cancer with radiotherapy
Acute radiation sickness dose
2-10 Sv to the whole body
Symptoms begin within a few hours.
Exposed to > 10 Sv to the whole body = death within 24 hours.
Chronic radiation sickness
Hair loss, cataracts, sterility, obliterative endarteritis.
Who can be damaged by non-deterministic effects of radiation?
Damage to patient and also future children (for male and female patients) = therefore somatic AND genetic.
Factors affecting dose of radiation
- Type of radiation - only interested in x-rays
- Tissues being irradiated
- Age of the patient
Dose limits per annum for: Classified worker, non-classified worker and general public.
The national radiological protection board estimate that the main dose for dental workers should be _____________.
<0.1mSv (never exceed 1mSv)
ALARP
As
Low
As
Reasonably
Practicable
How dangerous is a periapical radiograph in comparison to smoking?
1 in 200 people will die from smoking, compared with 1 in 5 million people dying from periapical.
What are two changes to the X-ray which can be made to reduce developing fatal malignancy?
Change from D speed to F speed (highest film possible), change collimator from round to rectangular.
Patients age - 10-20 multiplication factor for risk
2 times
Patients age - <10 multiplication factor for risk
3 times
Where does most of a person radiation dose come from?
84% from foods etc (bananas, avocado).
Average daily exposure 100 BED.
(15% from medicine and dentistry)
Ways to reduce dose
- Avoid taking unnecessary radiographs
- Film speed - use F speed
- kV of machine - higher = lower dose
- Rectangular collimator vs round
The intensity of a beam
The number of ‘photons’ in a beam at a specific place.
Therefore the further away you are from the source of radiation the less likely we are to be exposed to many x-ray photons.
Controlled area
Is the area around the patient and the X-ray tube where only the patient should be present, the rest of the controlled area should be a “no go zone”.
Controlled area size for an x-ray operating at <70kV
controlled area = 1.5m in diameter (this can change depending on the local rules)
In DDH, how far away from x-ray are you required to stand?
2m or behind appropriate shielding (led etc)
