Rad Prot practical aspects Flashcards

1
Q

DAP

A

dose area product
used in diagnostic radiology, EXCEPT CT

starting point for estimating patient effective dose
used to estimate scattered doses from patient
used to audit practice

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2
Q

DLP

A

dose length product
used for CT
starting point for estimating patient effective dose
used to estimate scattered doses from patient
used to audit practice

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3
Q

DAP calc

A

= xray beam area x absorbed dose

DAP meter - a parallel plate ionisation chamber mounted at xray tube

independent of distance from xray tube

will increase if field size increased
Gycm^2

look up tables required to convert DAP to organ or effective doses

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4
Q

DLP in CT calc

A

= CTDIvol * L

L scanned length

no DAP due to geometry
use pencil ionisation chamber

depends on exposure factors and beam width

mGy.cm

measure dose along z axis

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5
Q

CT dose index CTDI

A

mGy

area under curve/T

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6
Q

CTDIvol

A

takes into account pitch

measured using a phantom

= CTDIw / pitch

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7
Q

weighted CTDI

A

CTDIw = 1/3 CTDIcentre + 2/3 CTDIperiphery

mGy

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8
Q

exposure controls

A

most to least important

engineering controls and design features
safety features and warning devices
systems of work
PPE

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9
Q

Lead PPE

A

0.25mm will reduce scattered dose by approx 10 times at 100kV

0.35mm: nearly 15 times

scattered beam protection

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10
Q

TVL

A

tenth value layer

thickness of the material that reduces the dose rate to 0.1 of incident dose rate

eg. 22mm lead

2 TVL

reduces dose by 100 times

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11
Q

annual dose limits
employees

A

Effective 20 mSv

equiv:
eye lens 20
skin 500
extremities 500

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12
Q

classified person
dose expectations

A

E >6mSv
eye > 15
skin or extremity >150

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13
Q

estimating staff doses

A

dosimeter tech

thermo-luminescent dosimeters (TLDs)
optically stimulated luminescent (OSL) dosimeters
variety of electronic devices

must be approved by HSE

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14
Q

effective dose monitoring

A

measures body and skin dose
TLD or OSL

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15
Q

eye monitors

A

eye dose
TLD

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16
Q

extremity monitors

A

skin dose
TLD

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17
Q

DIL

A

dose investigation level

effective dose level set by employer and given in local rules

when exceeded, a review of working conditions is required to ensure doses are ALARP
(workload, equipment…)

staff monitored

set lower than dose limit
annual level required
equivalent doses

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18
Q

lead aprons

A

increase distance by 30cm, reduce effective dose by half

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19
Q

thyroid shields

A

reduction in effective dose by > 5 times with 0.35mm Pb

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20
Q

eye shields

A

reduction in eye dose limit to 20mSv per year

dose reduction 5-10 times

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21
Q

shielding materials
selection

A

depends on
radiation type and energy
thickness and weight
permanence
cost
optical transparency

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22
Q

shielding materials

A

lead sheet
lead glass and lead acrylic
concrete
brick

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23
Q

dose constraints

A

upper level of dose to an individual used at the design or planning stage

dose constraint < dose limit

0.3mSv for public
1 mSv for occupationally exposed workers

24
Q

designation of controlled area

A

designate if dose rate over working day > 7.5 micro Sv per hour

IDR (instantaneous dose rate)> 7.5
if employees untrained in rad prot in area

25
Q

barrier factor B

A

barrier transmission factor

dose constraint / (air kerma incident on barrier (t) x occupancy)

t = period over which dose delivered
occupancy = 1 for offices

B = annual dose constraint / annual dose to barrier

26
Q

sources of radiation (air kerma incident on barrier)

A

primary beam
secondary/scattered beam
leakage radiation

27
Q

shielding calculations

A

primary and scattered beam dose-rates or dap workloads
beam directions
workload (DAPs for xrays and radioactive materials/activity/dose rates for nu med)
floor plan and surrounding rooms: occupancies
distances to barriers
dose constraint

28
Q

primary beam

A

if primary beam unattenuated:
inverse square law
beam output data
exposure factors
patient dose data

if attenuated by patient:
use dose to detector

29
Q

scattered beam

A

scatter factors

30
Q

leakage

A

leakage radiation from tube housing

medical and dental guidance notes require that leakage is less than 1mGy per hour at 1m

below is negligible

31
Q

assessing facilities

A

barrier factor:
use radioactive source and appropriate detector:
calibrate for distance, thickness of barrier

check for gaps using source/detector or xray/film

32
Q

site monitoring
when to carry out

A

carried out
at installations or after modifications
periodic checks
following incidents

33
Q

Duty holders under IRMER
referrer

A

provides relevant clinical details
refers to gp

34
Q

Duty holders under IRMER
practitioner

A

weighs up risks
considers alternative methods
decide if the xray is justified

35
Q

Duty holders under IRMER
operator

A

ID patients
check exam is justified
check right protocol used
performs the exam

36
Q

Duty holders under IRMER
employer

A

put protocols in place
DRLs and SOPs
know who is trained to perform each role

37
Q

Duty holders under IRMER
MPE

A

medical physics expert

helps w optimisation
radiation protection
and patient dosimetry

38
Q

10 day rule

A

10-day rule stating that the abdominal area (lumbar spine, pelvis, coccyx, and hips) should not be irradiated after the 1st 10 days of one’s menstrual cycle.

for high dose > 10 mGy

39
Q

28 day rule
missed period

A

replace 10 day rule with a 28-day rule. This means that radiological examination, if justified, can be carried throughout the cycle until a period is missed. Thus the focus is shifted to a missed period and the possibility of pregnancy.

low dose exams

40
Q

typical fetal doses

A

0.001 - 50mGy

ensure doses are <100mGy to avoid deterministic effects

41
Q

mental retardation

A

loss of 30IQ points per Gy

42
Q

fetal irradiation and cancer

A

risk coefficient of inducing childhood cancer from radiation exposure is 10^-4 mGy^-1

1 in 10000 per mGy

after first 3 weeks of pregnancy

43
Q

procedures for people of reproductive potential

A

establish pregnancy
period overdue- treat as pregnant

12-55 years
ask children under 16

for exposures where the primary beam may irradiate the pelvis

44
Q

accidental exposure

A

person receives an exposure in error, no exposure of any kind intended

reportable:
1mSv effective dose or above for child
3mSv or above for adult

all modalities

due to systematic/human/procedural/equipment error

eg. electronic referrals, ID error, operator errors

45
Q

unintended exposures due to equipment malfunction

A

reported under IRMER

equipment that delivers radiation AND ancillary equipment that influences dose to the patient eg. software, contrast injectors

46
Q

unintended exposures risks

A

stochastic effects: increased cancer risk

deterministic tissue injuries

psychological harm

47
Q

reporting unintended exposures

A

notification no later than 2 weeks after discovering incident
final report no later than 12 weeks

report to CQC

report:
what happened
estimate of doses received
root causes and contributory factors
previous incidents similar
if local procedure was followed
corrective measures adopted
how to prevent in future

48
Q

average annual radiation dose in UK

A

natural background
2.3mSv per year

average annual dose
2.7mSv per year

49
Q

how legislation keeps doses ALARP

A

dose efficient equipment
equipment QA programmes
optimising scans
training
TRLs and patient dose audits

50
Q

DRLs

A

diagnostic reference levels

radiation employer sets DRLs

a dose level for typical examinations for groups of standard sized patients for broadly defined types of equipment

periodic audit of doses to be carried out and actions taken if consistently exceeded

51
Q

setting DRLs

A

National DRLs published based on 3rd quartile of data

local DRLs based on local audits
(based on median now)

52
Q

stochastic effects risk factors
risk of fatal cancer

A

5% per Sv

higher risk for children:
more radiosensitive
more time for effect to be expressed

53
Q

alternative to DAP meter
ESD

A

entrance surface dose

absorbed dose to air on beam axis at point of entry to the patient

ESD = incident absorbed dose x backscatter factor (BSF)

54
Q

BSF

A

back scatter factor

depends on
xray spectrum
xray field size
thickness of patient

55
Q

HVL

A

A material’s half-value layer (HVL), or half-value thickness, is the thickness of the material at which the intensity of radiation entering it is reduced by one half

higher beam HVL, higher BSF

56
Q

patient dose calculations

A

needed for individual patient if involved in radiation incident/found to be pregnant

info needed:
tube output data and filtration, kV, mAs, ..

DAP,

patient height and weight if useful

57
Q

IRMER17 vs IRR17

A

IRMER17:
protection of patients
referrer,practitioner,operator,MPE
DRLs
training
regulated by CQC

IRR17:
protection of staff and public
RPA,RPS
local rules
annual dose limits
training
regulated by HSE