Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

diagnostic radiology (ionising) > radiation risk and patient dosimetry > Flashcards

radiation risk and patient dosimetry Flashcards

1
Q

what are the units of absorbed dose

A

Gy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are the units of equivalent dose

A

Sv

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

eqn linking absorbed dose to equivalent dose

A

H_T=D x w_R

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are stochastic effects

A

prob. proportional to dose, no thresh

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

stochastic effect of interest

A

carcinogenesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

why is there a reduced probability of bad effect after a certain dose

A

because of e.g. cell kill

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what are deterministic effects

A

tissue reactions
only happen above a threshold where the severity becomes increased with dose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what does somatic effects mean

A

affect the irradiated individual

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are two somatic effects

A

carcinogenesis and deterministic effects

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what radiation effect is there no convincing evidence for

A

chromosome damage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is chromosome damage mechanism

A

breakage followed by faulty repair

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are some issues with a genetic risk assessment (3)

A
  1. only gonad exposure is relevant
  2. mutations may be recessive
  3. mutations may be unstable
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

problems estimating dose to an individual (2)

A
  1. different organs and tissues have different radiosensitivies
  2. doses to organs and tissues on uniformly distributed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

define absorbed dose and give the units

A

absorbed dose (D) = energy absorbed per unit mass (Gy)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what does equivalent dose take into account

A

differing biological effects induced by the same absorbed dose from radiations with different LET

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what does effective dose take into account

A

differing radiosensitivities of tissues and organs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what are the units of effective dose

A

sieverts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

evidence of stochastic effects

A

japanese survivors
early radiographers
uranium miners
radium dial painters

19
Q

definition of detriment

A

a measure of total harm arising form an exposure

20
Q

four components of detriment

A
  1. prob. of fatal cancer
  2. prob. of severe genetic effects
  3. relative length of life lost
  4. weighted prob. of non-fatal cancers
21
Q

average annual dose

A

2.7 mSv

22
Q

why are risk factors high for children (2)

A

greater opportunity for expression of induced effects

greater sensitivity of some forms of cancer

23
Q

why are there enhanced risks in utero

A

a small number of rapidly dividing cells may be radiosensitive

rel. small no. cells performing specific functions: possibility of abnormalities

24
Q

two types of stochastic effects

A

heritable effects (lack of data)
cancer induction

25
Q

examples of patient dose quantities (5)

A
  1. surface dose
  2. organ dose
  3. dose area product (total energy imparted)
  4. CT dose index
  5. effective dose
26
Q

surface dose pros

A

easily measured
easily calculated from radiographic factors

27
Q

surface dose cons (2)

A

no indication of volume irradiated

non aditive if beam position changes

28
Q

how to calculate surface dose from radiographic factors

A

use ionisation chamber to measure tube output

calculate
surface dose = tube output x inv. square factor x backscatter factor x mAs (used for the examination)

29
Q

units for tube output in air

A

mGy/mAs

30
Q

how to calculate organ dose

A

calculate from measured/calculated surface dose if organ position known
work out using the percentage depth dose and using normalised organ dose data available

31
Q

what is the percentage depth dose

A

the attenuation of the beam at the depth of the organ

32
Q

why use dose area product

A

the total energy imparted correlates reasonably well with risk

33
Q

when is DAP useful

A

when x ray beams vary in size and position

34
Q

what assumption is made for DAP

A

all the energy is absorbed

35
Q

DAP units

A

dose x area of the beam
Gy cm2

36
Q

cons of direct dap measurement

A

confined to surface usually
delay between measurement and readout
not retrospective

37
Q

pros of indirect dap measurement

A

retrospective estimates possible
not all factors may be routinely recorded
calibration needed if AEC is used
difficult in fluoro - use DAP meter

38
Q

how to perform CT scanner dosimetry

A

ion chamber measurements

39
Q

what are the ref dose quantities for CT called

A

CT dose index (CTDI)ho

40
Q

how to calculate CTDI

A

integrate D(x) (the dose profile across a slice) and divide by nominal slice width

41
Q

what is CTDI_w

A

weighted avg dose within the standard phantoms

42
Q

what is CTDI_vol

A

CTDI_w corrected for pitch or couch increment and the mAs used for the scan

43
Q

what is DLP

A

dose length product
CTDI_vol x increment length

44
Q
A

diagnostic radiology (ionising) (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions