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Med Imaging > Rad Prot practical aspects > Flashcards

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
barrier factor B
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
sources of radiation (air kerma incident on barrier)
primary beam secondary/scattered beam leakage radiation
27
shielding calculations
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
primary beam
if primary beam unattenuated: inverse square law beam output data exposure factors patient dose data if attenuated by patient: use dose to detector
29
scattered beam
scatter factors
30
leakage
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
assessing facilities
barrier factor: use radioactive source and appropriate detector: calibrate for distance, thickness of barrier check for gaps using source/detector or xray/film
32
site monitoring when to carry out
carried out at installations or after modifications periodic checks following incidents
33
Duty holders under IRMER referrer
provides relevant clinical details refers to gp
34
Duty holders under IRMER practitioner
weighs up risks considers alternative methods decide if the xray is justified
35
Duty holders under IRMER operator
ID patients check exam is justified check right protocol used performs the exam
36
Duty holders under IRMER employer
put protocols in place DRLs and SOPs know who is trained to perform each role
37
Duty holders under IRMER MPE
medical physics expert helps w optimisation radiation protection and patient dosimetry
38
10 day rule
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
28 day rule missed period
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
typical fetal doses
0.001 - 50mGy ensure doses are <100mGy to avoid deterministic effects
41
mental retardation
loss of 30IQ points per Gy
42
fetal irradiation and cancer
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
procedures for people of reproductive potential
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
accidental exposure
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
unintended exposures due to equipment malfunction
reported under IRMER equipment that delivers radiation AND ancillary equipment that influences dose to the patient eg. software, contrast injectors
46
unintended exposures risks
stochastic effects: increased cancer risk deterministic tissue injuries psychological harm
47
reporting unintended exposures
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
average annual radiation dose in UK
natural background 2.3mSv per year average annual dose 2.7mSv per year
49
how legislation keeps doses ALARP
dose efficient equipment equipment QA programmes optimising scans training TRLs and patient dose audits
50
DRLs
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
setting DRLs
National DRLs published based on 3rd quartile of data local DRLs based on local audits (based on median now)
52
stochastic effects risk factors risk of fatal cancer
5% per Sv higher risk for children: more radiosensitive more time for effect to be expressed
53
alternative to DAP meter ESD
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
BSF
back scatter factor depends on xray spectrum xray field size thickness of patient
55
HVL
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
patient dose calculations
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
IRMER17 vs IRR17
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

Med Imaging (14 decks)

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