patient dosimetry in ctindico.ictp.it/event/a12208/session/4/contribution/3/...iec methods other...
TRANSCRIPT
![Page 1: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/1.jpg)
John M. Boone, Ph.D., FAAPM, FSBI, FACR
Professor and Vice Chair (Research) of Radiology Professor of Biomedical Engineering
University of California Davis Medical Center Sacramento, California
Patient Dosimetry in CT: what to measure and estimate;
why and how?
2013 ICTP/IAEA Training Course on Radiation Protection of Patients Trieste
![Page 2: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/2.jpg)
Disclosures Paid Consultant to:
Varian Imaging Systems
Alston and Bird LLC
CardioInsight
DXray
Royalty Income from:
Lippincott Williams and Wilkins
Samsung Corporation
Research Funding from:
Stanford Research Institute
University of Pittsburgh
Siemens Medical Systems
Hologic Corporation
National Institutes of Health (NIBIB)
![Page 3: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/3.jpg)
Trieste 15 Sept 2013
![Page 4: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/4.jpg)
Why
What
How: conventional CT systems
How: cone beam CDT systems IEC methods
Other approaches
Measure versus Estimate
Summary
Patient Dosimetry in CT: what to measure and estimate; why and how?
![Page 5: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/5.jpg)
5
80 x 80 matrix 8 grey scale (3 bit images)
EMI Mark 1: 1972
water bag for bolus 4 minute scan (120 sec/image) overnight reconstruction
Images courtesy ImPact Website (UK)
![Page 6: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/6.jpg)
6
Modern helical multi-slice CT
![Page 7: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/7.jpg)
7
![Page 8: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/8.jpg)
8
axial coronal sagittal
high resolution three dimensional imaging
![Page 9: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/9.jpg)
9
Allan M. Cormack
Godfrey N. Hounsfield
Nobel Prize for Medicine 1979
![Page 10: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/10.jpg)
10
Helical CT
Multi-slice CT
technology advancements have led to greater CT use
![Page 11: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/11.jpg)
531 mm
331 mm 200 mm
CT x-ray tube output
GE VCT 120 kV 32.3 mGy/100 mAs @ IC 600 mAs 1/6 rotation 432 mGy @ isocenter ISL = 2.57 1.1 Gy @ skin
~60°
![Page 12: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/12.jpg)
![Page 13: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/13.jpg)
Why
What
How: conventional CT systems
How: cone beam CDT systems IEC methods
Other approaches
Measure versus Estimate
Summary
Patient Dosimetry in CT: what to measure and estimate; why and how?
![Page 14: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/14.jpg)
Firs
t B
rain
CT
Fir
st W
ho
le B
od
y C
T
Firs
t 4
rth
Gen
erat
ion
CD
T
Spir
al C
T
Du
al S
lice
CT
(aga
in)
mA
Mo
du
lati
on
Meg
a H
U x
-ray
tu
be
s
Fou
r Sl
ice
CT
8 t
o 4
0 s
lice
CT
64
slic
e C
T
Du
al S
ou
rce
CT
Flyi
ng
foca
l sp
ot
Ad
apti
ve D
ose
Co
llim
atio
n
Epila
tio
n c
ause
d b
y C
T
Evolution of CT Scanners and Dosimetry
CTDIFDA
CTDIW CTDIVOL
TG-204
TG-111 CTDI
TG-233
SB-1237
TG-200
TG-220
19
72
19
74
19
74
19
89
19
92
19
94
19
95
19
97
20
00
20
00
20
04
20
06
20
07
20
09
20
10
20
13
A brief history of the….
![Page 15: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/15.jpg)
15
CTDI:
Computed Tomography Dose Index
![Page 16: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/16.jpg)
16
The solid state CT detector
T
n=16
0.625 mm
nT = 16 × 0.625 mm = 10 mm
![Page 17: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/17.jpg)
17
cone angle
fan angle
z-axis
Multiple Detector CT
Many detector arrays along z nT is the width of the x-ray beam at IC
nT
![Page 18: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/18.jpg)
1( )CTDI D z dz
nT
![Page 19: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/19.jpg)
do
se
position
Z=0 -Z +Z
1( )CTDI D z dz
nT
( )D z
CTDI
![Page 20: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/20.jpg)
50
100
50
1( )
mm
mm
CTDI D z dznT
![Page 21: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/21.jpg)
position
do
se
Z=0 -Z +Z
50
100
50
1( )
mm
mm
CTDI D z dznT
100 mm
![Page 22: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/22.jpg)
position
do
se
Z=0 -Z +Z
50
100
50
1( )
mm
mm
CTDI D z dznT
100 mm
This equation requires table movement, either axial or helical CT scans which traverse 100 mm It is not valid for a stationary table scan such as with CT perfusion or CT fluoroscopy
![Page 23: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/23.jpg)
50
100
50
1( )
mm
mm
CTDI D z dznT
100 mm
position
do
se
Z=0 -Z +Z
100 mm
![Page 24: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/24.jpg)
CTDI - based Dose Metrics
32 cm diameter PMMA
16 cm diameter PMMA
100 mm pencil chamber
The Tools…….
Adult Body Phantom
Head Phantom
Peds Body Phantom
![Page 25: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/25.jpg)
CTDI - based Dose Metrics
The Methods…….
CTDI100 peripheral
CTDI100 center
![Page 26: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/26.jpg)
26 Measuring CTDI100 in the real world
![Page 27: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/27.jpg)
The CTDI “Head” Phantom in position for CTDI100 measurement
The CTDI “Body” Phantom in position for CTDI100 measurement
![Page 28: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/28.jpg)
CTDI - based Dose Metrics
The Mechanics…….
CTDI100 peripheral
CTDI100 center + ⅓ ×
⅔ ×
weighted CTDI, CTDIw
dose = 1 / pitch
Volume CTDI, CTDIvol = CTDIw / pitch
W Leitz, et al., CT dose assessment – a practical approach, Radiat Prot Dosim 1995; 57: 377
![Page 29: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/29.jpg)
CTDI - based Dose Metrics
The CTDIw is the planar average dose to the central slice of the phantom in a series of slices spanning 100 mm
![Page 30: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/30.jpg)
30
L
Which scan has more “dose”?
L
…to first order, the dose is the same
![Page 31: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/31.jpg)
31
L
DLP = CTDIvol × L (mGy • cm)
Dose Length Product (DLP):
DLP is related to the total energy deposited in the patient
![Page 32: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/32.jpg)
32
Effective Dose ≈ DLP × k
Effective Dose per DLP
(AAPM TG-96)
Region of Body
Head and neck
Head
Neck
Chest
Abdomen / pelvis
trunk
k (mSv/[mGy-cm])
0.0031
0.0021
0.0059
0.014
0.015
0.015
![Page 33: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/33.jpg)
33
dose length product (mGy-cm)
The CT scanners now have a dose report that state the DLP. One can use these values with the conversion factors above to estimate the effective dose for the patient
Effective Dose per DLP
![Page 34: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/34.jpg)
CTDI - based Dose Metrics Free-in-air measurement (no phantom)
CTDIfree-in-air or CTDIair
![Page 35: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/35.jpg)
CTDI - based Dose Metrics
CTDI100 (center & peripheral)
The Tools
CTDIw
CTDIvol
DLP
The Metrics
The Methods
CTDIair
![Page 36: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/36.jpg)
![Page 37: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/37.jpg)
Why
What
How: conventional CT systems
How: cone beam CDT systems IEC methods
Other approaches
Measure versus Estimate
Summary
Patient Dosimetry in CT: what to measure and estimate; why and how?
![Page 38: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/38.jpg)
CTDI - based Dose Metrics
average peripheral measurement
effect of table attenuation
![Page 39: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/39.jpg)
50
100
50
1( )
mm
mm
CTDI D z dznT
mGy mm
c mGy × 100 mm = 100 c mGy.mm
For a chamber reading out in air kerma
100cK L
CTDIn T
kerma reading chamber length
![Page 40: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/40.jpg)
CTDI - based Dose Metrics
100 mm
1507.3 mR
corrections
1. exposure to kerma correction 1507.3 mR / (114.5 mR/mGy) = 13.16 mGy
2. chamber reading air kerma 3. correction for nT
13.16 mGy x 100 mm = 1316 mGy.mm
1316 mGy.mm / 20 = 65.8 mGy (CTDI100)
nT = 20 mm (e.g.)
![Page 41: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/41.jpg)
data are approximated beam
detected e =
detected
beam
penumbra
detector arrays
CTDI - based Dose Metrics
Dependency on collimated beam width (nT)
![Page 42: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/42.jpg)
CTDI - based Dose Metrics
Dependency on collimated beam width (nT) (but MDCT has reduced use of this)
thin collimation thick collimation
![Page 43: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/43.jpg)
![Page 44: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/44.jpg)
impactscan.org (UK)
Sue Edyvean
![Page 45: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/45.jpg)
Why
What
How: conventional CT systems
How: cone beam CDT systems (stationary table) IEC methods
Other approaches
Measure versus Estimate
Summary
Patient Dosimetry in CT: what to measure and estimate; why and how?
![Page 46: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/46.jpg)
Toshiba Aquillion 1: 320 x 0.5 mm = 160 mm
![Page 47: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/47.jpg)
do
se
position
Z=0 -Z +Z
1( )CTDI D z dz
nT
50
100
50
1( )
mm
mm
CTDI D z dznT
100CTDI
CTDIe
![Page 48: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/48.jpg)
CTDI - based Dose Metrics
100 mm
1507.3 mR
cone beam CT
nT > 100 mm
![Page 49: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/49.jpg)
100CTDI
CTDIe
![Page 50: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/50.jpg)
100CTDI
CTDIe
![Page 51: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/51.jpg)
do
se
position
Z=0 -Z +Z
![Page 52: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/52.jpg)
do
se
position
Z=0 -Z +Z
,( )
1
mc
free in air n T i
i
LCTDI D
n T
![Page 53: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/53.jpg)
do
se
position
Z=0 -Z +Z
, ( 20 )c
free in air REF eg mm
K LCTDI
n T
![Page 54: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/54.jpg)
50
,
100,
,50
1( )
( )
mm
free in air n T
REF
REF free in air REFmm
CTDICTDI D z dz
n T CTDI
![Page 55: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/55.jpg)
Why
What
How: conventional CT systems
How: cone beam CDT systems IEC methods
Other approaches
Measure versus Estimate
Summary
Patient Dosimetry in CT: what to measure and estimate; why and how?
![Page 56: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/56.jpg)
do
se
position
Z=0 -Z +Z
100 mm ion chamber
18 mm thimble chamber
![Page 57: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/57.jpg)
CT perfusion (stationary table)
![Page 58: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/58.jpg)
do
se
position
Z=0 -Z +Z
CTDIw
peak dose
Stationary table perfusion CT (j rotations)
dose = peak dose × j rotations
position
do
se
Z=0 -Z +Z
100 mm
![Page 59: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/59.jpg)
Why
What
How: conventional CT systems
How: cone beam CDT systems IEC methods
Other approaches
Measure versus Estimate
Summary
Patient Dosimetry in CT: what to measure and estimate; why and how?
![Page 60: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/60.jpg)
Measure versus Estimate
In general, it is best to say that doses are estimated, and not
calculated or measured. This conveys the proper notion that
CT dosimetry is an imprecise science, which it is.
![Page 61: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/61.jpg)
Why
What
How: conventional CT systems
How: cone beam CDT systems IEC methods
Other approaches
Measure versus Estimate
Summary
Patient Dosimetry in CT: what to measure and estimate; why and how?
![Page 62: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/62.jpg)
62
CTDI100mm
center periphery
CTDIw = 1/3 CTDIcenter + 2/3 CTDIperiphery
CTDIvol = CTDIw / pitch
DLP = CTDIvol x length irradiated
dose length product (mGy-cm)
measure CTDI100 [center]
measure CTDI100 [periphery]
The phantom is either a 16 cm diameter acrylic (head) or a 32 cm diameter (body) phantom
![Page 63: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/63.jpg)
63
CTDI is a good measure of CT dose to a large plastic
phantom, but is not a stand-alone metric for patient dose
etcetera….
Med Phys 2003
![Page 64: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/64.jpg)
![Page 65: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/65.jpg)
![Page 66: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/66.jpg)
Why
What
How: conventional CT systems
How: cone beam CDT systems IEC methods
Other approaches
Measure versus Estimate
Summary
Patient Dosimetry in CT: what to measure and estimate; why and how?
![Page 67: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/67.jpg)
![Page 68: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/68.jpg)
![Page 69: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/69.jpg)
![Page 70: Patient Dosimetry in CTindico.ictp.it/event/a12208/session/4/contribution/3/...IEC methods Other approaches Measure versus Estimate Summary Patient Dosimetry in CT: what to measure](https://reader034.vdocuments.us/reader034/viewer/2022050115/5f4c950160999d2e02470249/html5/thumbnails/70.jpg)