Risk and Dose Flashcards Preview

Year 3 Radiography > Risk and Dose > Flashcards

Flashcards in Risk and Dose Deck (37):
1

what is meant by absorbed dose (D) and unit

measure of amount of energy absorbed from radiation beam per unit mass of tissue, Gray (Gy, 1 Joule/kg)

2

explain how absorbed dose can vary in effect even if it is the same amount

depends how the energy is packaged: more damaging if energy fired in one go

3

explain equivalent dose (H) and units

allows potential harm from different types of radiation to be considered
H= absorbed dose (D) x radiation weighting factor (Wr)
unit= sievert (Sv)

4

radiation weighting factor (Wr) for
a) X-rays and gamma rays
b) beta particles
c) protons and neutrons
d) alpha particles

radiation weighting factor (Wr) for
a) X-rays and gamma rays: 1
b) beta particles: 1
c) protons and neutrons: 5-10
d) alpha particles: 20

5

interpret the radiation weighting factor of x rays and gamma rays

equivalent dose in sieverts= absorbed dose in Grays

6

explain effective dose (E) and unit

allows doses from different investigations or different parts of body to be compared, because some parts of body more radiosensitive than others
effective dose= dose equivalent x tissue weighting factor (Wt) (sieverts)
if more than 1 organ exposed, effective dose is sum of all effective doses to all exposed organs

7

what is the most radiosensitive part of the body?

gonads

8

what do each of these dosimetry abbreviations stand for:
D
H
E

D: absorbed dose
H: equivalent dose
E: effective dose

9

what medical examination gives the highest radiation dose?

CT chest

10

what medical examination gives the lowest radiation dose?

dental intraoral film

11

how long would it take to receive equivalant dose from background radiation compared to effective dose of intraoral x rays?

16 hours

12

how long would it take to receive equivalant dose from background radiation compared to effective dose of dental panoramic film?

3 days

13

how many mSv from
a) flight to Spain return
b) UK average
c) Cornwall
d) intraoral x rays
e) oral panoramic
f) chest x ray
g) head CT
h) barium meal
i) chest CT
j) mammography

a) flight to Spain return: 0.02mSv
b) UK average: 2.6 mSv/yr
c) Cornwall: 7.8mSv/yr
d) intraoral x rays: 0.001-0.008mSv
e) oral panoramic: 0.02mSv
f) chest x ray: 0.02mSv
g) head CT:2mSv
h) barium meal:3mSv
i) chest CT:8mSv
j) mammography:1.24mSv

14

risk of malignancy from 1 intraoral film using
a) traditional x-ray set and D-speed film
b) 70kV x-ray set and E-speed film

a) traditional x-ray set and D-speed film: 1/ 2 million
b) 70kV x-ray set and E-speed film: 1/20 million

15

risk of malignancy from 1 panoramic film

multiplication risk factors for age groups

0.21-1.9/ 1 million

16

explain collective dose

total effective dose to population
collective dose = effective dose x population
unit= man-Sv

17

3 groups of population for purposes of limiting radiation dose

patients
occupationally exposed (workers)
general public

18

4 things to consider before prescribing pt an x ray

1. correct assessment of indications
2. expected diagnostic yield (how useful is x ray)
3. way in which results influence diagnosis/ treatment
4. clinician having adequate knowledge of physical properties and biological effects of ionising radiation

19

2 classifications of radiation workers

classified (>6mSv / year)
non-classified

20

what are comforters and carers and dose limits

people who willingly undergo radiation exposure to support/ comfort pt, eg parent or carer
no dose limits but dose constraints

21

3 golden rules of dose reduction

distance
shielding
time

22

distances of controlled area

1m for sets up to 70kV
1.5m for sets above 70kV
(preferably operator >2m away from pt and x ray tube, not in line of primary beam)

23

what law of physics does radiation follow? explain

inverse square law
intensity of radiation reduces to 1/4 as distance is doubled

24

other rules of controlled area

-warning light illuminated when x ray on
-warning notice provided when controlled area extends to door

25

4 materials used for shielding

1. lead
2. lead rubber/glass
3. concrete
4. barium plaster

26

2 ways to reduce dose to operator and comforter/ carer

1. stand behind lead glass screen
2. lead-rubber apron

27

when to use thyroid collars

if thyroid gland in primary beam

28

what is collimation?

x ray beam shaping to minimum required to cover image receptor

29

6 ways to use dental x ray set to reduce x ray dose

1. higher kV (60-70kVp)
2. rectangular collimation
3. adequate aluminium filtration
4. long focus to skin distance (>20cm)
5. accurate timer
6. adequate warning signals

30

how to reduce dose by quality assurance

-regular checks of equipment (x-ray and processing)
-image quality evaluation and audit

31

advantage of digital imaging over film 5

1. quicker
2. less pt dose
3. less storage requirements
4. constantly evolving
5. environmentally better

32

2 dose measurements in radiography

1. entrance surface dose (ESD) miliGrays, mGy. max dose to tissues, measured using thermoluminescent dosimeters (TLDs), ionisation chambers

2. dose-area product (DAP): max dose to tissues

33

who should have personal dosemeters?

people exposed to more than 1mSv/year
(>100 intraoral or 60 panoramic films per week)

34

how do film badges work

contain photographic film to show how much radiation youve been exposed to

35

advantages and disadvantages of film badges

advantages:
-cheap
-permanent record
-may be reassessed
-can see type of radiation received

disadvantages:
-processing required

36

how do thermoluminescent dosimeters (TLD) work?

lithium fluoride crystals release stored radiation energy as light when heated

37

advantages and disadvantages of TLDs

advantages:
-sensitive
-reusable
-provide quick read-out
-no processing required

disadvantage:
-destructive read-out
-expensive
-limited info on energy of radiation received