Radiation Protection - Practical Aspects 1+2 Flashcards
1
Q
When is dose area product used?
A
diagnostic radiology except CT
2
Q
When is dose length product used?
A
CT
3
Q
Purpose of DAP and DLP?
A
starting point to estimate patient effective dose
estimate scattered dose from patient
audit practice
4
Q
How to calculate DAP?
A
x-ray beam area x absorbed dose
5
Q
DAP is _______ with distance if there is no attenuation
A
invariant
6
Q
Why are conventional ionisation chambers not appropriate to measure doses in CT?
A
due to geometry
7
Q
What is used to measure doses in CT?
A
pencil ionisation chamber
TLD array
8
Q
What does pencil ionisation chamber depend on?
A
exposure factors
beam width
9
Q
What axis is the dose measured along in CT?
A
z axis
10
Q
What are CT doses measured in? and with what unit?
A
air or phantom
mGy.cm
11
Q
How is CT dose index measured?
A
for a single rotation using a pencil ionisation chamber
12
Q
CTDI equation
A
CTDI = dose profile in mGy.cm/ nominal beam width
area under curve/T
13
Q
CTDI unit
A
mGy
14
Q
What does CTDI vol account for?
A
pitch, measured using a phantom
15
Q
What is weighted CTDI?
A
1/3 CTDI at centre + 2/3 CTDI at periphery
16
Q
why is weighted CTDI calculated?
A
measured for standard protocols
17
Q
how is weighted CTDI related to CTDI vol?
A
CTDI vol = CTDI w/pitch
18
Q
How is weighted CTDI measured?
A
measured in standard perspex phantom (head and body sizes) at mAs used for examination
Units mGy
19
Q
dose length product equation
A
CTDI vol *L
where L is scanned length
20
Q
what does dose length product relate to?
A
dose from complete examination
21
Q
HSE advice for a risk assessment under IRR17?
A
Identify the hazards
Decide who might be harmed and how
Evaluate the risks and decide on precaution
Record your findings and implement them
Review your assessment and update if necessary
22
Q
hierarchy of exposure controls
A
engineering controls - safety features and warnings - systems of work - ppe
23
Q
what does I131 emit?
A
gamma and beta
24
Q
employee annual effective dose limit?
A
20 mSv
25
employee equivalent eye lens dose limit?
20 mSv
26
employee skin averaged 1cm2 equivalent dose limit?
500 mSv
27
employee extremities equivalent dose limit?
500 mSv
28
Classified person
employee likely to annually exceed:
6mSv effective dose
15mSv eye lens equivalent dose
150mSv extremity equivalent dose
29
What special requirements exist for classified persons?
dose monitoring, record keeping, medical surveillance
30
What devices are used to estimate staff doses?
thermo luminescent dosimeters
optically stimulated luminescent dosimeters
variety of electronic devices
31
When should monitors be approved for use by HSE?
if used by classified worker
32
What does effective dose monitoring measure?
Hp(10) body dose, Hp(0.07) skin dose
33
Where should effective dose monitoring devices be worn?
between shoulders and waist, under protective clothing
34
What do eye monitors measure?
estimate Hp(3) commonly using TLD
35
What types of eye monitors exist?
forehead or clipped to glasses on eye closest to source
collar outside of protective clothing
36
What do extremity monitors measure?
Hp(0.07) skin dose commonly with TLD
37
Where are extremity monitors attached?
ring, finger stalls, bracelet
wear dose meter on digit which will receive max dose
38
What is the ratio between the tip and base of the finger?
4-6
39
What is the dose investigation level?
effective dose level set by employer and given in local rules
when the level is exceeded a review of working conditions is required to ensure doses are ALARP
40
What is a typical dose investigation level?
1-4 mSv depending on work
41
What can the DIL not exceed?
15mSv
42
who should be notified if the DIL is exceeded?
HSE (health and safety executive)
43
How should a DIL be set?
lower than dose limit - aim to keep doses ALARP
annual level required - monthly not
can set for equivalent doses too but not required
44
How are DIL's implemented?
staff monitored on monthly or quarterly basis depending on risk
ensure doses reviewed throughout the year so that excess can be identified
45
Other reasons for high doses?
badge lost/dropped in controlled areas
exposed during travel/ medical exposure
deliberate exposure
46
Increasing distance by ____ reduces effective dose by ~ half
30cm
47
% change in dose increasing Pb apron 0.25mm to 0.5mm
few %
48
why are thyroid shields used?
thyroid is particularly radiosensitive
49
0.35mm Pb reduces effective dose by ___ times
at least 5
50
eye dose limit reduced to ____ with eye shields
20 mSv
51
Eye shields reduce dose by ____
5-10x
52
How is scatter to clinicians eyes from below front and side limited?
wraparound design minimises gaps
comfort
53
Under IRR17 if working with ionising radiation
1) employer must consult an RPA
2) ensure there is appropriate notification, registration or consent
3) carry out risk assessment
4) appoint RPS
5) ensure staff are trained and aware of local rules
54
A room should be designed with the aim of _____
keeping doses ALARP and ensuring dose limits are not exceeded
55
Room design should consider:
- dose constraints
- occupancies outside the facility
- choice of shielding material
- provision for dismantling and decommissioning
- ease of cleaning and decontamination
56
Selection of shielding material is dependent on:
- radiation type and energy
- thickness and weight
- ability to combine structure/shielding
- uniformity of material
- permanence
- cost
- optical transparency
57
shielding materials
lead sheet
lead glass and acrylic
concrete and concrete blocks
brick
barium plaster
gypsum plasterboard
58
What data about the beam is more appropriate when considering materials?
broad beam attenuation data
59
What data is important about shielding materials?
density and uniformity
60
Tenth value layer
thickness of material which reduces the dose rate to 0.1 of the incident dose rate
it is energy dependent
61
the fraction of the beam transmitted through material x is described by B =
B=10^(-x/TVL)
62
for shielding calculations we need to know:
- primary beam and scattered beam dose rates or DAP workload
- beam directions
- workload
- distances to barriers
- dose constraint
63
Dose constraint
upper level of dose to an individual used at the design or planning stag
64
Dose constraint
upper level of dose to an individual used at the design or planning stage
dose constraint < dose limit
65
Occupationally exposed workers dose constraint
1mSv
66
members of the public when optimising protection from a single source
0.3mSv per year
can account for occupancy
67
ACOP designation of a controlled area
dose rate over working day > 7.5 µSvhr-1
OR
instantaneous dose rate > 7.5 µSvhr-1 if employees untrained in radiation protection have access to area
68
instantaneous dose rate
dose rate averaged over 1 minute
69
sources of radiation (air kerma on barrier)
1. primary beam
2. scattered beam
3. leakage radiation (linacs)
70
scatter depends on
kV, angle, area of x-ray beam at scattering point
71
Typical dlp for a chest-abdo-pelvic ct scan
1000 mGy.cm
72
leakage radiation
comes from tube housing - heavily filtered
73
medical and dental guidance notes require leakage to be less than __
1m Gy per hour at 1m
74
Why are facilities assessed?
- specified level of protection exists
- check gaps in shielding (joints, door and window frames, sockets pipes breach walls)
75
How to assess facilities by finding barrier factor
use radioactive source/x-ray system
calibrate for distance, thickness of barrier
check for gaps using source/detector or xray/film
76
Site monitoring should be carried out
at installations or after modifications
periodic checks
following incidents
77
Duty Holders under IRMER17
referrer
practitioner
employer
operator
medical physics expert
78
conditions for exposing people of reproductive potential
age range 12-55
exposures irradiating between knees and diaphragm
79
procedures for people of reproductive potential
establish pregnancy
if definitely pregnant, rejustify exposure accounting for fetus
if pregnancy cannot be excluded, use a low dose <10mGy
80
where pregnancy cannot be excluded and a high dose is required:
treat as pregnant
to avoid carry out procedures within first 10 days after period
81
CSAUE
clinically significant accidental unintended exposures under IRMER17
82
accidental exposure
person receives an exposure in error when no exposure of any kind was intended
83
accidental exposures are reportable at:
1mSv in a child effective dose
3mSv in an adult effective dose
84
unintended exposure
where an exposure was intended but person receives an exposure significantly higher or different to intended
85
examples of unintended exposure
dose received, wrong modality/technique, wrong anatomy, radiopharmaceutical or timing of exposure
86
unintended exposures are caused by
procedures, systematic or human error
equipment malfunction
87
unintended exposures due to equipment malfunction are reported under
IRMER
88
"equipment" malfunction in unintended exposures refers to
equipment delivering radiation and ancillary equipment influencing dose e.g., contrast injectors, software, PACS and RIS
89
SAUE incidents reported to CQC:
notification no later than 2 weeks post incident
final report no later than 12 weeks post incident
