Radiation Protection

Question 1

What is Absorbed Dose and what are it’s units?

Answer 1

Measure of the amount of energy deposited in a medium per unit mass of the medium.
Units = Gray (Gy)

Question 2

What is absorbed dose measured in?

Answer 2

Measure in Joules/kg

Question 3

What is the subunit of absorbed dose?

Answer 3

milligrays (mGy) (x10^-3)

Question 4

What is the equivalent dose?

Answer 4

Takes into account the different radio-biological effectiveness of different types of radiation.

Question 5

How is equivalent dose calculated?

Answer 5

Equivalent dose = absorbed dose x radiation weighting factor

Question 6

What is the weighting factor?

Answer 6

Weighting factor = Wr
X-rays, gamma rays and beta particles Wr = 1
Alpha particles Wr = 20

Question 7

What is the unit of equivalent dose?

Answer 7

Sievert (Sv)
Sub-unit = millisieverts (mSv) (x10^-3)
microsieverts (x10^-6)

Question 8

What is the equivalent dose, measured in Sieverts, equal to?

Answer 8

It is equal to the absorbed dose, measured in Grays, as the radiation weighting factor = 1.

Question 9

What is the effective dose?

Answer 9

The effective dose allows doses from different investigations of different parts of the body to be compared.
It converts the dose to the equivalent whole body dose, as some body parts are more sensitive to radiation than others.
Use a tissue weighting factor (Wt)

Question 10

How is effective dose calculated and what is it measured in?

Answer 10

Effective dose (E) = equivalent dose x tissue weighting factor
Unit = Sievert
Sub-unit = millisievert

Question 11

What does the term dose usually mean?

Answer 11

Effective dose

Question 12

What is the UK’s background radiation?

Answer 12

Average 2.5mSv per year

Question 13

What are the two types of biological affects of radiation?

Answer 13

Somatic = affecting those irradiated, either deterministic or non-deterministic (stochastic)
Genetic = affecting offspring of those irradiated, non-deterministic (stochastic)

Question 14

What is meant by Deterministic affects of radiation?

Answer 14

The effects will occur, there is a threshold dose at which the effect begins to occur. Above the threshold, the severity of the effect increases with dose.

Question 15

What are some deterministic effects?

Answer 15

Cataracts, gastrointestinal upset, suppression of erythropoiesis .

Question 16

Do deterministic effects of radiation occur in dentistry?

Answer 16

No, they shouldn’t

Question 17

What are the effects of radiation on the unborn child?

Answer 17

Related to dose so deterministic
Susceptible when the organs are developing (2-9 weeks)
Results in malformations (reduced growth) or death

Question 18

Name 6 non-deterministic effects (Stochastic) of radiation?

Answer 18

It may occur, development is random
No threshold at which stochastic events begin to occur
Any dose of radiation may cause stochastic effects
Probability of event occurring increases with dose
Severity of event not effected by dose, all or nothing
Leukaemia’s and solid tumours

Question 19

Do non-deterministic (stochastic) effects of radiation occur in dentistry?

Answer 19

Yes

Question 20

Which cells are the most radiosensitive?

Answer 20

Those with high mitotic rate
those that are going to undergo many future mitoses
Those most primitive in differentiation
Lymphocytes and oocytes which are highly differentiated and non-dividing.

Question 21

Effects of radiation can be direct or indirect, explain each.

Answer 21

Direct - Interacts with biological macromolecules (DNA, RNA, proteins and enzymes) causing ionisation and damage
Indirect - water is abundant in the body - most common damage.
Hydrogen and hydroxyl fee radicals produced by action of radiation on water
Free radicals can form toxic substances such as hydrogen peroxide.

Question 22

What happens when DNA is changed/damaged?

Answer 22

DNA is the primary mechanism for cell death, mutation and carcinogenesis
Strands break, loss/change of base, disrupt bonds between strands

Question 23

Can DNA be repaired?

Answer 23

Yes, but if both strands are broken close to each other, there can be misrepair as the intact strand is usually used as a template.

Question 24

What is the risk of cancer in Scotland?

Answer 24

Currently the risk of getting cancer in their lifetime in Scotland is 1 in 3.

Question 25

What are the genetic effects of radiation?

Answer 25

Radiation to reproductive organs may damage the DNA in sperm/egg. This may result in congenital abnormalities in offspring of those irradiated but no certainty as there is no threshold. As with all stochastic effects, it is difficult to prove

Question 26

``` What is the additional risk of cancer from each of the following Chest X-ray Head CT Intraoral Panoramic ```

Answer 26

``` Risk of fatal cancer Chest X-ray - 1 in 1,000,000 Head CT - 1 in 10,000 Intraoral - 0.06-0.7 in 1,000,000 Panoramic - 0.29-1.9 in 1,000,000 ```

Question 27

Why are younger patients more at risk?

Answer 27

These patients have more dividing cells so are more radiosensitive and have a longer lifespan over which to develop an affect

Question 28

What are the three principles of radiation protection?

Answer 28

Justification Optimisation Dose Limitation

Question 29

Explain justification of x-rays.

Answer 29

Exposure cannot be carried out unless it is justified | The benefit from examination must outweigh the detriment from exposure

Question 30

Explain optimisation.

Answer 30

For each exposure, the operators must ensure that the doses arising from the exposure are kept as low as reasonably practicable and consistent with the intended diagnostic purpose.

Question 31

What is ALARP?

Answer 31

``` As Low As Reasonably Practicable ```

Question 32

What is the inverse square law?

Answer 32

The intesity is inversely proportional to distance^2, therefore ensure staff stand a sufficient distance from the patient and not in the direction of the primary beam.

Question 33

What is the controlled area?

Answer 33

Designated area to protect staff and other persons

Question 34

How to ensure it is a controlled area?

Answer 34

Generally within the primary beam until it has been sufficiently attenuated by distance or shielding Within 1.5m of the tube and patient in any other direction Usually exists only when x-rays are being generated

Question 35

Who should be in the controlled area?

Answer 35

Only the patient

Question 36

What should be the size of the controlled area?

Answer 36

The size depends on the kV of the machine, 1.5m for under 70kV but size depends on local rules.

Question 37

What is the distance for the controlled area in DDH?

Answer 37

2m for all machines or behind an appropriate shield

Question 38

What warnings should there be in place?

Answer 38

A visible light and an audible noise when x-rays are being produced The operator should be able to prevent access to the controlled area Control panels, switches, isolators etc. outside the controlled area

Question 39

How should x-ray exposure be monitored?

Answer 39

Not normally required if the staff don't have to enter the controlled area, unless the individual doses are likely to exceed 1mSv per year Or if there is a high workload ie >100 intra-orals or >50 panoramics per week.

Question 40

Is there any justification for routine use of lead aprons for patients during dental radiography?

Answer 40

No, however thyroid collars should be used in those few cases where the thyroid may be in the primary beam.

Question 41

When is the foetus most susceptible?

Answer 41

During organogenesis (2-9 weeks)

Question 42

Would there be any need to enquire about pregnancy for a dental radiograph?

Answer 42

No, as the primary beam will not be irradiating the pelvic area.