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Shielding for Diagnostic X-rays:UK Guidance
Jerry WilliamsRoyal Infirmary of EdinburghRoyal Infirmary of Edinburgh
BIR/ IPEM Working Party ReportBIR/ IPEM Working Party Report
British Institute of Radiology
Institute of Physics and Engineering in Medicine
Working Party:
David Sutton Jerry Williams Colin Martin Don McIntosh Tony
Institute of Physics and Engineering in Medicine
David Sutton, Jerry Williams, Colin Martin, Don McIntosh, Tony Cotterill, Graham Hart, David Gallacher
Publication date: 2000
BIR/ IPEM Working Party Report
Content:
BIR/ IPEM Working Party Report
• Design criteria and dose constraints
• Primary & Secondary radiations• Primary & Secondary radiations
• Building materials
• X-ray transmission factorsay t a s ss o acto s
• Assessment of shielding
• Worked examples
Working Party:
David Sutton Jerry Williams Colin Martin Don McIntosh Tony David Sutton, Jerry Williams, Colin Martin, Don McIntosh, Tony Cotterill, Graham Hart, David Gallacher
Publication date: 2000
dRadiation Sources
• Radiography (film/ screen)• Radiography + Fluoroscopy• Radiography + Fluoroscopy• Angiography
CT ( i l li )• CT (single slice)• Mammography• Dental• DEXA• DEXA
h lkThis talk
• Design criteria• Transmission factors• Transmission factors• Shielding materials
P i d S d R di ti• Primary and Secondary Radiations
Design Criteria: Design Criteria: Dosimetric Quantities
• Dose limits–Effective dose, E mSvEffective dose, E mSv
• Dose monitoringOperational quantity–Operational quantity
–Personal dose equivalent, Hp(d) mSv
Shi ldi l l ti• Shielding calculations–Air kerma, K mGy
Design Criteria
• Dose constraint (people)– Based on public dose limit (1 mSv/ year)
A li d ( ff bli )– Applied to everyone (staff + public)– 0.3 mGy/ year (6 µGy/ week)
• Occupancy factor • Occupancy factor – ≥5%– Dose to be < 6 mGy/ year– (Controlled area)
• Dose constraint (film or CR)/ d ( / k)– 0.4 µGy/ day (2 µGy/ week)
fOccupancy factors
• Based on individual occupancy• Examples:p
Office 100%Reception area 100%Reception area 100%X-ray control room 100%Patient examination room 50%Corridor 20%Corridor 20%Toilets/ bathrooms 10%Outdoor area with seating 10%Store rooms 5%Store rooms 5%Unattended waiting rooms 5%
fX-ray Transmission factors
• Adopted Archer’s empirical model1−
⎤⎡ ⎞⎛ γγα
αβ
αβ1 ⋅⋅
⎥⎦⎤
⎢⎣⎡ −⎟
⎠⎞⎜
⎝⎛ += teB
• Used Simpkin’s α, β, γ values• Added data for brick and barium Added data for brick and barium
plaster
Archer et al (1983) Health Physics, 44, 507.
Simpkin (1995) Health Physics, 68, 704
h ld lShielding material
UK Standard lead thicknesses
Code t mm3 1.324 1.805 2.246 2.65
Primary and Secondary Primary and Secondary Radiations
• Leakage radiationg• Primary/ transmitted beams• ScatterScatter
X-ray Tube LeakageX ray Tube Leakage
Assumptions:•Tube leakage factor: 150 kV/ 3.3 mA
•Field size: 1000 cm2
•Distance: 1 m from tube/ patient
WP Recommendation:WP Recommendation:
•Leakage contribution may be ignored
Primary & Transmitted Primary & Transmitted Radiation
• Fluoroscopy– Beam restricted to
image intensifier/ flat X-raybeam
image intensifier/ flat panel detector
– Detector has > 2mm lead equivalent
Patient
lead equivalent
• Mammography
Imagingdevice
Radiography: Film dose method
• Dose to film/ imaging plate– 400 speed system– Dose ≤10 µGy
Dose ≤10 µGy
• Lead equivalence (100 kV)– Cassette
• 0 19 mm• 0.19 mm– Cassette + grid
• 0.26 mm– Cassette/grid/tableCassette – Cassette/grid/table
• 0.8 mm– Cassette/grid/chest Bucky
• 0 7 mm
Bucky system
• 0.7 mm
Lead equivalence data derived from Dixon (1994) Med Phys, 21, 1785
Radiography: Film dose method
• Dose to film/ imaging plate
– 400 speed system– Dose ≤10 µGyDose ≤10 µGy
• Lead equivalence (100 kV)– Cassette
• 0 19 mm• 0.19 mm– Cassette + grid
• 0.26 mm– Cassette/grid/table– Cassette/grid/table
• 0.8 mm– Cassette/grid/chest Bucky
• 0 7 mm• 0.7 mm
Attenuated primary: limiting HVLAttenuated primary: limiting HVL
Limiting HVL: = ln(2) / α1
Limiting HVL: ln(2) / α
0.1 to eDD ⋅α−=
0 2
0.3
VL m
m
0.01
Tran
smis
sion
0.1
0.2
Lim
iting
H
0.001
T
040 60 80 100 120
kV0.0001
0 0.5 1 1.5 2 2.5 3
Lead thickness mm
Radiography: ESD methodRadiography: ESD method
• Unattenuated primary beam
p y– Beam outside patient
• Entrance Surface Dose (ESD)• Situations include
– Beam not collimated to cassette– Beam not directed to Bucky
• Examples– Chest radiography– Cross table radiography– Out of Bucky radiography (e.g.
extremities)
extremities)• Area of wall irradiated
– Not easy to predict– Variable– Variable
lExamples
Chest Radiography (film dose)Chest Radiography (film dose)
• ParametersParameters– 100 films/ week– 90 kV– ESD = 0.15 mGy– Film dose = 10 µGy– FFD = 1.8 m– FSD = 1.4 m
Fil ll 0 7 – Film-wall = 0.7 m
Best Radiographic Practice
Calculation (Film-dose method)
• Attenuated kerma at wall per week:Film dose x Workload x ISL correction
mGy52.07.08.1
8.110010102
3 =⎥⎦⎤
⎢⎣⎡
+××× -
⎦⎣
• No of HVLs required (6 µGy/ week) = 6.5 • Limiting HVL of lead @ 90 kV = 0.23 mmLimiting HVL of lead @ 90 kV 0.23 mm• Total equivalent lead thickness = 1.5 mm• Additional lead shielding =
0 8 0.8 mm
Chest Radiography (ESD)Chest Radiography (ESD)
• ParametersParameters– 100 films/ week– 90 kV– ESD = 0.15 mGy– Film dose = 10 µGy– FFD = 1.8 m– FSD = 1.4 m
Fil ll 0 7 – Film-wall = 0.7 m
Calculation (ESD method)( )• Worst case assumption:
• Beam size greater than patient and Bucky system
• Unattenuated kerma at wall per week:ESD x Workload x ISL correction
mGy7.47.08.1
4.110015.02
=⎥⎦⎤
⎢⎣⎡
+××
• Maximum transmission permitted= 6x10-3/ 4 7= 6x10 3/ 4.7= 0.0013
• Lead shielding @ 90 kV1.4 mm
Summary
• Best practice –Beam collimated to patient/ image Beam collimated to patient/ image
plate/ Bucky–0.8 mm lead
• Poor practice–Beam outside patient and BuckyBeam outside patient and Bucky–1.4 mm lead
Scatter
Scatter ModelNCRP 49 method
400FKaK us ⋅⋅=
Ks – scatter kerma; Ku – primary kermaF– Field size (cm2); a – scatter factorTrout and Kelly (1972), Radiology, 104, 161
Ku . F ⇒ Area-air kerma product (AKP) orArea-air kerma product (AKP) orDose area product (DAP)
DAPSK DAPSKs ⋅=
hWhy DAP?
• No assumptions on field size• Availability of DAP data• Availability of DAP data
–Requirement in UK legislation to record patient doserecord patient dose
–DAP preferred patient dose metric (fluoroscopy and radiography)(fluoroscopy and radiography)
–National surveys of patient dose
Scatter factor normalised to DAP (S)Scatter factor normalised to DAP (S)12
m2 )-1
125 kVp
8
10µG
y.(G
y.cm 100 kVp
85 kVp 70 kVp 50 kVp
4
6
r fac
tor,
S µ
0
2
0 30 60 90 120 150 180
Scat
ter
0 30 60 90 120 150 180
Angle of scatter
( ) ( )[ ]1f85kVdbS 234 θθθθ
JR Williams (1996) Br J Radiol, 69, 1032
( ) ( )[ ]1f85kVedcbaS 234 +−×+θ+θ+θ+θ=
Scatter factor normalised to DAP (S)
12
-1
Scatter factor normalised to DAP (S)
8
10
Gy.
(Gy.
cm2 )-
125 kVp100 kVp 85 kVp 70 kVp 50 kVp
4
6
fact
or, S
µG
a -1.04E-07b 3 27E 05
0
2
0 30 60 90 120 150 180
Scat
ter f b 3.27E-05
c -2.75E-03d 8.37E-02e 1 58E+000 30 60 90 120 150 180
Angle of scatter
( ) ( )[ ]1f85kVdbS 234 θθθθ
e 1.58E+00f 5.99E-03
( ) ( )[ ]1f85kVedcbaS 234 +−×+θ+θ+θ+θ=
JR Williams (1996) Br J Radiol, 69, 1032
Calculation vs measurement
Cli i l li tiMeasured/ Calc doseNo of DAP/ week Ave Calc Mean Min Max
Interventional Radiology (liver disease) 8 520 0.71 0.22 0.02 0.42Abdominal + lower limb angiograpy 8 1120 2.15 0.17 0.02 0.43
Clinical application positions Gy cm2 Dose mGy
Cardiac angiography 7 780 0.81 0.99 0.71 1.26Cerebral angiography 7 460 1.48 0.97 0.67 1.23Ba contrast studies (o/c tube) 9 430 0.66 0.74 0.50 1.13B t t t di ( / t b ) 10 960 1 62 0 28 0 05 0 86Ba contrast studies (u/c tube) 10 960 1.62 0.28 0.05 0.86General Radiography 10 460 0.96 0.64 0.30 1.06
Validation of scatter data by Validation of scatter data by Monte-Carlo
Scatter fraction (S) @ 85 kV12
Measured
6
8
10
Gy
cm2
MeasuredMC
2
4
6
S µG
y/ G
00 30 60 90 120 150 180
Angle
Comparison with NCRP 147
Scatter fraction (S) @ 85 kV12
UK
6
8
10
Gy
cm2 )-1
UK
NCRP 147
MonteCarlo
2
4
6
S µG
y (G
00 30 60 90 120 150 180
Angle
Differences in scatter factors?
• Phantom• X-ray spectrum• X ray spectrum• Measurement methods
Method in practicep12
m2 )-1
125 kVp
8
10µG
y.(G
y.cm 100 kVp
85 kVp 70 kVp 50 kVp
4
6
r fac
tor,
S µ
0
2
0 30 60 90 120 150 180
Scat
ter
( )
0 30 60 90 120 150 180
Angle of scatter
( ) ( )[ ]1f85kVedcbaS 234 +−×++++= θθθθ
h d ( )Method in practice (1)
0 6
0.8
1.0
doseθ d
0 2
0.4
0.6
Rel
ativ
e
r
0.0
0.2
0 30 60 90 120 150 180
S tt i l
( )[ ] ( ) 12max cmGyµGy5.2kV031.0S
−+×=
Scattering angle
( )d = 1 m; θ = 117°
θ d = 1 m
∫∫ ⋅= θ
θθd
d)(SS15030
ave ∫ θd
h d ( )Method in practice (2)
• Save over C-arm rotation – (30 to 150°)(30 to 150 )
• Smax for parallel beam
kV Smax Save
50 4.05 3.73
70 4.67 4.30
85 5.14 4.72
100 5 60 5 15100 5.60 5.15
125 6.38 5.86
b dTo be continued…..
• Application examples–FluoroscopyFluoroscopy–Radiography
• Comparisons with NCRP 147• Comparisons with NCRP 147