Risk and dose

Question 1

What is the unit of absorbed dose?

Answer 1

Gy (gray)

Question 2

What is 1 gray?

Answer 2

1 joule of energy removed from the beam by interaction with a 1kg block

= not a lot of energy but effect is dependent on how the energy is packaged (I.e. Individual particles have less of an impact than a mass of particles)

Question 3

What is equivalent dose (H)?

Answer 3

A measure which allows the potential harm (radio biological effectiveness) from different types of radiation to be considered

Question 4

How do you calculate equivalent dose?

Answer 4

Equivalent dose = absorbed dose (D) X radiation weighting factor (WR)

Question 5

What are the units of equivalent dose?

Answer 5

Sv (Sievert)

Question 6

What is the radiation weighting factor?

Answer 6

The quality factor (Q) / ionising capacity 
Varies between radiation types: 
- X-rays and gamma rays = 1
- beta particles = 1
- protons and neutrons = 5-10
- alpha particles = 20 

Protons, neutrons and alpha particles = greater mass deposited in a smaller area = greater ionising capacity
N.b where radiation weighting factor = 1 then the number of Gy=Sv

Question 7

What is effective dose (E)?

Answer 7

Allows doses from different investigations of different parts of the body to be compared (because it will vary between tissues)

Question 8

How do you calculate effective dose?

Answer 8

Effective dose = Equivalent dose X tissue weighting factor

Question 9

What are the units of effective dose?

Answer 9

Sv (sievert)

Question 10

Why is the effective dose important?

Answer 10

Different parts of the body (e.g. Go ads and lens etc.) are more radio sensitive than others

Question 11

If more than 1 organ is exposed what is the total effective dose?

Answer 11

The sum of the effective doses to all exposed organs

Question 12

How much dose is a patient allowed to recite every in a year?

Answer 12

As much as it takes to diagnose and treat them effectively BUT NEEDS JUSTIFICATION SO USE ALARP

Question 13

Order these dental and medical investigations from low effective dose (mSv) to high:
Barium meal, panoramic film, dental intraoral film, CT chest, CT head, Chest X-ray and mammography…

Answer 13

Dental intraoral film 
Panoramic film 
Chest X-ray 
Barium meal 
CT head 
CT chest 
Mammography

Question 14

How many hours of natural background radiation is equivalent to the effective dose for dental intraoral films?

Answer 14

16

Question 15

How many hours of natural background radiation is equivalent to the effective dose for panoramic film?

Answer 15

3 days

Question 16

What is the risk from 1 intraoral film?

Answer 16

1 malignancy in every 2 million exposures (traditional X-ray set and D-speed film)
1 malignancy in every 20 million exposures (70kV set and E-speed film)

Question 17

What is the risk from 1 panoramic film?

Answer 17

Using modern equipment

Risk for fatal cancers = 0.21 - 1.9 malignancies over million exposures s

Question 18

Risk factors for dying in any 1 year…

Answer 18

Smoking 10 cigarettes a day 
All natural causes, age 40 
All kinds of violence or poisoning 
Influenza
Accident on the road
Leukaemia 
Accident at home 
Accident at work 
Radiation (working within radiation industry) 
Homicide
FROM 2 DENTAL BITEWING RADIOGRAPHS
Lightening strike 
Release of radiation from nearby power station

Question 19

Why may dose vary for a single intraoral film?

Answer 19

• different X-ray tube (round/ collimating)

- different detector systems (film speeds/ digital)

Question 20

Due to the huge variation in doses what do we need to do regularly?

Answer 20

Monitor and use diagnostic reference levels

Question 21

What does film speed determine?

Answer 21

How sensitive a film is to radiation
(Higher letter = more expensive but more sensitive)
-> decreases exposure for same quality

Question 22

What is absorbed dose (D)?

Answer 22

A measure of the amount of energy absorbed from the radiation be a per unit mass tissue/loss of energy of the beam

Question 23

Why do children have a higher multiplication factor for risk of cancer than adults?

Answer 23

Children’s cells are undergoing more replication so any damage is amplified

Question 24

What is the multiplication factor for risk at 30 years?

Answer 24

1

Question 25

Risk in relation to age.... Multiplication factors:

Question 26

What is collective dose?

Answer 26

A measure used when considering the total effective dose to the population

Question 27

How do you calculate collective dose?

Answer 27

Collective dose = effective dose X population

Question 28

What are the units for collective dose?

Answer 28

Man-sievert (man-Sv)

Question 29

Who determines dose limitation?

Answer 29

The international commission on radiological protection (ICRP)

Question 30

Which 3 categories is the population divided into for dose limitation?

Answer 30

Patients Occupationally exposed General public

Question 31

What is the dose limit for patients?

Answer 31

There isn't one

Question 32

What should the decision to carry out a radio graphic investigation be based on (4)?

Answer 32

- the correct assessment of the indications - the expected diagnostic yield I.e. Usefulness - the way the results are likely to influence the diagnosis and subsequent treatment - the clinicians having an adequate knowledge of the physical properties and biological effects of ionising radiation

Question 33

What is the dose limit for the occupationally exposed?

Answer 33

Depends on level of occupational exposure and the risk involved: Classified workers Non-classified workers "The risk to any worker who receives full dose limit will be such that the worker will be at no greater risk than a worker in another hazardous but non radioactive environment"

Question 34

What exposure is required for an occupationally exposed individual to be a classified worker?

Answer 34

Dose >6mSv per annum

Question 35

What is the dose limitations for comforters and carers?

Answer 35

They don't have a dose limit but they have dose constraints

Question 36

What classes an individual as a comforter and carer?

Answer 36

An individual that willingly incurs an exposure in the support and comfort of another undergoing/ who has undergone a medical exposure

Question 37

What are the 3 golden rules of dose reduction?

Answer 37

1. Distance 2. Shielding 3. Time

Question 38

What law does distance follow?

Answer 38

The inverse square law

Question 39

What controlled area (IRR99) is needed for sets operating up to 70kV?

Answer 39

1.0m

Question 40

What controlled area (IRR99) is needed for sets operating above 70kV?

Answer 40

1.5m (Preferably the operator should be able to stand 2m or more away from the patient and X-ray beam but not in the line of the primary beam)

Question 41

What should happen when a controlled area extends to a door?

Answer 41

A warning notice should be provided at the entrance to indicate when radiography is in progress

Question 42

What needs to be visible throughout the exposure?

Answer 42

X-ray tube and warning light should be visible throughout the exposure

Question 43

Which materials can be used for shielding?

Answer 43

Lead (Pb) Lead rubber/lead glass (Pb equivalent in mm) Concrete Barium plaster

Question 44

How do we reduce the dose to operators/comforters/carers?

Answer 44

Stand behind lead screen If necessary hold/ wear lead rubber apron (n.b. There is no justification for the routine use of lead aprons for patients in dental radiography as no real benefit and aprons may block radiograph which may need retaking)

Question 45

When should thyroid collars be used?

Answer 45

If the thyroid is in the primary beam

Question 46

How do we reduce the dose to innocent bystanders?

Answer 46

Close X-ray room doors (local rules) Perform X-rays in a room only unless Only allow those required in the room

Question 47

How do we change time to reduce exposure?

Answer 47

Limit the amount of time exposed to radiation

Question 48

Which other ways can we reduce dose to the patient?

Answer 48

Collimating Careful technique (adequate training, accurate positioning, exposure selection and good explanations) Digital radiography Perform appropriate projections (follow established protocols) Equipment Quality assurance

Question 49

When dose a dental X-ray set give a lower dose?

Answer 49

``` Higher kV (60-70) Rectangular collimating Adequate aluminium filtration Long focus to skin distance (>20cm) Accurate timer Adequate warning signs Restriction of exposure to dentition (decreases effective dose by 50%) ```

Question 50

How does long focus to skin distance

Answer 50

Angle of field smaller = doesn't spread as much in tissue

Question 51

How do we manage quality assurance?

Answer 51

Regular checks of equipment (at least every 3 yrs) = includes processing equipment Image quality evaluation and audit

Question 52

What are the advantages of digital imaging over film?

Answer 52

``` = quicker results (direct/indirect) = potentially less patient dose = less storage requirements = constantly evolving = environmentally better ```

Question 53

What are the different types of dose measurements?

Answer 53

Entrance surface dose (esd) | Dose-area product (dap)

Question 54

What is entrance surface dose?

Answer 54

Represent the max dose in tissues | Measured using thermoluminescent dosimeters (tlds) and ionisation chambers

Question 55

What are the units for entrance surface dose?

Answer 55

mGy

Question 56

What is dose area product?

Answer 56

Measures ionisation and areas of ionising

Question 57

What is the units for dose area product?

Answer 57

mGy/cm^2

Question 58

When should a person wear a personal dosimeter?

Answer 58

When risk assessment indicates that individual doses could exceed 1mSv / yr In practice... Should be considered for those staff who's weekly workload exceeds 100 intraoral/ 50 panoramic films

Question 59

What is a film badge?

Answer 59

Photographic film under Windows of different thicknesses

Question 60

What are the advantages of film badges?

Answer 60

Cheap Provides a permanent record Can be reassessed Provides information on type of radiation received

Question 61

What are the disadvantages of film badges?

Answer 61

Requires processing

Question 62

What is thermoluminescence?

Answer 62

A form of luminescence when stored radiation energy is emitted As light on heating

Question 63

Which material do thermoluminescent dosimeters contain?

Answer 63

Lithium fluoride crystals

Question 64

What are the advantages of thermoluminescent dosimeters?

Answer 64

Sensitive Reusable Provide quick read out No processing required

Question 65

What are the disadvantages of thermoluminescent dosimeters?

Answer 65

Destructive read out Expensive Provides limited I for on energy of radiation received (don't know type exposed to)