Radiation Safety m3 Flashcards
What are the Biological effects of radiation?
Those we know will occur
- Called DETERMINISTIC (non stochastic)
Those which may occur
- Called NON DETERMINISTIC (stochastic)
What are the Deterministic effects of radiation?
- Definitely occur with specific doses*
- Threshold dose*
- Below threshold the effect does not occur*
(a) Acute - Radiation sickness 2-10 Sv whole body irradiation
- Death >10 Sv whole body irradiation
(b) Chronic
- Hair loss
- Cataracts
- Sterility
- Obliterative endarteritis
What are Non deterministic effects of radiation?
- Occur at random – chance or probability*
- “Just like playing the lottery”*
- No threshold dose*
- Damage affects patient & also future children
- Somatic & Genetic effects
- Amount of damage not related to dose
- Less chance of damage with low dose
- Somatic effects – development of malignancy
- Genetic effects - congenital abnormality which may include malignancy
Which type of effects are we likely to have in dentistry?
Non deterministic - And that’s the problem
Whar are Factors affecting dose of radiation?
- Type of radiation – we are interested only in x-rays
- Tissues being irradiated
- Age of the patient
What are doses for bitewing/ periapical, DPT or maxillary occlusal
- Bitewing/periapical 0.0003 – 0.022
- DPT 0.0027 – 0.038
- Maxillary occlusal 0.008
What are the new Dose limits per annum?
Classified worker 20 mSv
Non-classified worker 6 mSv
General public 1 mSv
We should aim for general public status
What is the estimated mean does for dental workers?
NRPB estimated mean dose for dental workers <0.1mSv
Recommended that should never exceed 1mSv - dose limit for public
There are no set dose limits for patients but ……ALARP…?
As
Low
As
Reasonably
Practicable
How dangerous are x-rays?
Smoking 1:200
Roads 1:17,000
Air crash 1:1,000,000
Periapical 1:5,000,000
DPT 1:1,000,000
What are the Estimated risks of developing fatal malignancy from x-ray examinations?
- Dental intra-oral 70kV, D speed, round 1 in 1M
- Dental intra-oral 70kV, F speed, rectangular 1 in 10M
- DPT average 1 in 1,000,000
- Standard occlusal 1 in 2,500,000
The younger the pateint the more likely they are to develop adverse affects from radiation.
More than half the pateint x-rays in dentistry are below age of 25.
What is the Multiplication factor for risk of cancer by age?
- < 10 = 3
- 10 -20 = 2
- 20 - 30 = 1.5
- 30 - 50 = 0.5
- 50 - 80 = 0.3
- >80 = negligible
We are exposed to ionisation radiation a lot and our main exposure is from natural background radiation including food.
Natural background incl. food 84%
Fallout & radioactive waste <1%
Medical & Dental 15%
Occupational <1%
List some foods that are radioactive – mainly from radioactive potassium?
- Brazil nuts
- Butter beans
- Bananas
- Potatoes
- Carrots
- Red meat
- Avocado
- Beer
- Water
- Peanut butter
What are practical means of dose reduction?
- Avoid unnecessary radiographs
- Use of Selection Criteria
- Film speed – preferably use F speed
- (Digital radiography may help)
- kV of machine – higher the kV, lower the dose
- Rectangular collimation
- Collimated DPT views
- Regular servicing of machines
- Knowledge & Understanding!
Intensity & the Inverse Square Law – why are they important?
Intensity of x-ray beam is the number of photons in a beam at a specific place.
Intentensity of radiation is proportional to 1/distance2
i.e practically the further we are from exposure the less likely we are to be exposed to many x-ray photons
