Patient Dose Estimates
from CT Examinations
John M. Boone, Ph.D.
Professor and Vice Chairman of Radiology
Professor of Biomedical Engineering
University of California, Davis
Patient Dose Estimates
from CT Examinations
Why are we here?
Definitions
CT “dosimetry” in the real world
Chairman, AAPM Science Council
Chairman, ICRU CT* Committee
Perspectives from the ICRU Committee
Summary
*Image Quality and Patient Dose in Computed Tomography, ICRU Report 93
www:myhealthfinder.com/hcac/CTreport04.pdf
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emergency room CT scans
emergency room CT use rate
in press, Journal of the American College of Radiology
out-patient CT use rate
in-patient CT use rate
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The radiation levels from CT has caught the eye of the public
CT scans per patient
mean = 2.88
let’s go measure the
CTDI100
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Bob Dixon
So what’s wrong with the CTDI100?
David Brenner
Patient Dose Estimates
from CT Examinations
where it all began…….
Why are we here?
Definitions
CT “dosimetry” in the real world
Perspectives from the ICRU Committee
Summary
4
CTDI
=
1
nT
+7 T
−7 T
D ( z ) dz
CTDI
=
1
nT
+7 T
−7 T
D ( z ) dz
nT
100 mm
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CTDI
=
1
nT
CTDI
=
1
nT
+7 T
−7 T
+7 T
−7 T
D ( z ) dz
CTDI
=
1
nT
+7 T
−7 T
D ( z ) dz
D ( z ) dz
So what’s wrong with the CTDI100?
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So what’s wrong with the CTDI100?
So what’s wrong with the CTDI100?
ρ = 1.19
ρ
1.0
28 cm
32 cm
So what’s wrong with the CTDI100?
16 cm diameter PMMA cylinder
scan length
So what’s wrong with the CTDI100?
32 cm diameter PMMA cylinder
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Patient Dose Estimates
from CT Examinations
100 mm pencil chamber
Why are we here?
Definitions
CT “dosimetry” in the real world
Perspectives from the ICRU Committee
Summary
8
Computation of effective dose (ImPACT of UK) based on
Standard patient geometry and Monte Carlo derived tables
Patient Dose Estimates
from CT Examinations
Why are we here?
Definitions
CT “dosimetry” in the real world
Perspectives from the ICRU Committee
Summary
ICRU: Image Quality and Patient Dose in CT
John M. Boone (US)
James Brink (US)
Sue Edyvean (UK)
Jacob Geleijns (Netherlends)
Walter Huda (US)
Wolfram Leitz (Sweden)
Cynthia McCollough (US)
Michael McNitt-Gray (US)
ICRU Sponsors:
Willi Kalender (Germany)
Kunio Doi (US)
Peter Dawson (UK)
ICRU: Image Quality and Patient Dose in CT
A. CT scanner radiation output measurement
B. Dose to the Reference Patient - DRP
C. Dose to the Individual Patient
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A. CT scanner radiation output measurement
A. CT scanner radiation output measurement
A-1 CTDI100
A-1 CTDI100
A-2 Rise to Equilibrium (TG-111)
A-2 Rise to Equilibrium (TG-111)
A-3 D(z) of CT beam
A-3 D(z) of CT beam
A-4 D(x, z) of CT beam
A-4 D(x, z) of CT beam
A. CT scanner radiation output measurement
A. CT scanner radiation output measurement
A-1 CTDI100
A-1 CTDI100
A-2 Rise to Equilibrium (TG-111)
A-2 Rise to Equilibrium (TG-111)
A-3 D(z) of CT beam
A-3 D(z) of CT beam
A-4 D(x, z) of CT beam
A-4 D(x, z) of CT beam
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A. CT scanner radiation output measurement
B. Dose to the Reference Patient - DRP
B-1 Definition of the Reference Patient
A-1 CTDI100
B-1.1 Size Range
A-2 Rise to Equilibrium (TG-111)
B-1.2 Standard Scans (DRP-X)
A-3 D(z) of CT beam
B-2 Dose assessment
A-4 D(x, z) of CT beam
B-2a Monte Carlo measurements
B-2b physical measurements
B-3 Utility of DRP-X
Standard Scans
Size Range
thoracic
> 50 cm (XXL)
45.1-50 cm (XL)
abdomen
pelvis
40.1-45 cm (L)
head
35.1-40 cm (M)
30.1-35 cm (S)
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B. Dose to the Reference Patient - DRP
B-1 Definition of the Reference Patient
B-1.1 Size Range
B-1.2 Standard Scans (DRP-X)
B-2 Dose assessment
B-2a Monte Carlo measurements
B-2b physical measurements
B-3 Utility of DRP-X
Monte Carlo Modeling
physical dose measurements
θ
θ
abdomen
abdomen
αx2 + βy2 = r
vendor
bow tie
spectrum
etc.
r
r’ = a + bθ + cθ2 + dθ3 + ….
0
0.5π
1π
θ
1.5π
αx2 + βy2 = r
Monte Carlo Simulations
2π
TLDs
r
r’ = a + bθ + cθ2 + dθ3 + ….
0
0.5π
1π
θ
1.5π
2π
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Doses from XX CT Scanner in Room 4
(mGy per 100 mAs)
B. Dose to the Reference Patient - DRP
Pediatric Female Male
B-1 Definition of the Reference Patient
abdomen
B-1.1 Size Range
B-1.2 Standard Scans (DRP-X)
B-2 Dose assessment
B-2a Monte Carlo measurements
xx
xx
xx
xx
xx
yy
yy
yy
yy
yy
zz
zz
zz
zz
zz
Xs
S
M
L
XL
xx
xx
xx
xx
xx
yy
yy
yy
yy
yy
zz
zz
zz
zz
zz
thorax
B-2b physical measurements
B-3 Utility of DRP-X
C. Dose to the Individual Patient
Xs
S
M
L
XL
Dose metrics
Dose units
C-1 Doses to patients measured in mGy
C-2 Individualized deterministic dose computation
average tissue dose (mGy)
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Individualized Dose Estimates
DICOM header
kVp, mAs eff., pixel size, slice thickness, etc.
Determination of Primary Dose
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Determination of Scatter Dose
CT image
primary dose image
P
S
CT image
primary dose image
S
1000 bone
HU
0 tissue
-1000 air
µ scatter
µ total
S
µ scatter
µ total
scatter to primary ratio
(per voxel) - SPR
HU
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Dose(x,y,z) = Doseprimary(x,y,z) + Dosescatter(x,y,z)
CT image
primary dose image
scatter dose image
Determination of Dose
from CT Examinations
three dimensional dose distribution
primary dose
Why are we here?
Definitions
scatter dose
CT “dosimetry” in the real world
Perspectives from the ICRU Committee
total dose
Summary
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average tissue dose (mGy)
THE END
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