Transcript Breast Dose Reduction in Routine Chest CT Through the Use

CTDI Measurement with
OSL Dosimeters
Scott Emerson, MS
Beaumont Hospital, Royal Oak
Collaboration of this Project
 Yongguang
Liang, Ph.D.
 Subhash Danak M.S.
 Dennis Aurand, M.S.
 Cheryl Culver-Schultz, M.S.
Outline
 CTDI
Background
 Methods with nanoDots
 Results and Analysis
 Discussion and Conclusion
Objective
 Investigate
the viability of optically
stimulated luminescent (OSL) dosimeters
in CTDIvol measurement
 Compare OSL dose to:


Scanner displayed CTDIvol
Ion chamber measured CTDIvol
 Investigate
future applications
Conventional CTDI Measurements
 CTDI100 measured
with one axial CT scan
using a 100-mm long CT “pencil” ionization
chamber and the standard CTDI phantom
(head, 16 cm, and body, 32 cm).
1
2
CTDI w  CTDI 100 ,center  CTDI 100.edge
3
3
Limit of Conventional CTDI
Measurements[1]
 CTDI
is defined for axial scanning
 Application to dose in helical scanning is
conceptually presumptuous
 Current CTDI100-based measurements are
becoming more limited as CT beams widen
along z



Move from fan to cone beam
Exclude contributions radiation scattered beyond
the 100-mm range of integration along z
In turn, underestimates the cumulative dose
OSL Dosimeters
– carbon-activated
aluminum oxide crystals (Al2O3:C)
 OSL is exposed to radiation, electrons
trapped in metastable energy state
 Once stimulated by green laser light,
electrons de-excite and emit visible light
 Amount of visible light emitted is
proportional to cumulative absorbed dose
 OSL dosimeter is reusable
 OSL dosimeters
Use of OSL Dosimeters

Skin dose measurements
1. CT Dosimetry: Comparison of Measurement Techniques
and Devices [2]
2. Skin dose study for CT brain perfusion protocols at
Beaumont and other clinics
a) “Skin Dose in Routine CT Brain Perfusion Studies
Using Siemens 64 slice, Definition Dual Source, and
Flash CT Scanners”, Yongguang Liang et. al., accepted
as Alternate Paper for 2010 RSNA annual meeting
b) “Radiation Dose of Patient Receiving CTA and CTP
Studies of Brain”, P Lin and D Hackney, Med. Phys. 37,
3116 (2010) (Beth Israel Deaconess Medical Center,
Boston, MA )
 Fluoroscopy entrance skin dose measurements
Measurement Set Up

Equipment used:
1. Siemens Somatom Sensation 16-slice CT
scanner
2. Landauer OSL dosimeters and InLight®
microStar system for reading dose
3. Standard CTDI phantom, acrylic rods with a
notch at the middle to hold the OSL dosimeters.
4. Radcal model 9015 with 100 mm pencil ion
chamber
Notch of Acrylic Rod
Positioning OSL on CTDI Phantom
CT Image of OSL Dosimeters
Scan Protocols
Experiment Procedure
 OSL dosimeters
were placed in the center
rod, as well as the 12, 3, 6, and 9 clock
positions


All outer positions can be averaged to be
CTDI100,edge dose
Comparable to center and peripheral with ion
chamber
 100
mm scan length to compare to
CTDI100 measured by the pencil ion
chamber
Experiment Procedure
 10
minute post-exposure delay allows the
signal from the transient thermal traps to
dissipate before reading the dose [4]
 Exposure were repeated four times for
each protocol

Scanner reproducibility previously proven with
ion chamber measurements during annual
tests
Data Analysis

OSL reader calibrated to 80 kVp beam


Tissue-to-air correction of 1.06 mGy/mGy


Energy correction of 1.12 for 120 kVp, according to
Landauer report[5].
From AAPM Report No. 96[6]
Now OSL doses can be compared to CTDI
results measured by ionization chamber.
“correct” result = “raw” result x 1.12 / 1.06
Dose (mGy)
Results of Three Protocols
70
65
60
55
50
45
40
35
30
25
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15
10
5
0
ADULT HEAD
12 o'clock
ADULT ABDOMEN
3 o'clock
6 o'clock
PEDIATRIC ABDOMEN
9 o'clock
Center
OSL Results vs Displayed
CTDIvol and Ion Chamber CTDIvol
Discussion
 OSL dosimeters
in agreement with
scanner display (<±5%) and ion chamber
measurement (<±8.2%)
 Measurements were done for axial scans
(adult head protocol) and helical scans
(adult, pediatric abdomen protocol).
Conclusion and Future Study
 OSL Dosimeter
can be used to measure
the CTDI with a comparable accuracy to
the conventional ionization chamber
measurement for a scan length of no more
than 10 cm
 OSL can be used to measure CT dose for
both axial and helical scans
AAPM TG 111 Applications
 OSL can
be used to measure CT dose for
longer scan length (>10 cm) and larger
beam widths
 Study is needed to compare the OSL to
the “Farmer type” chamber suggested by
AAPM Task Group 111
References
1.
2.
3.
4.
5.
6.
American Association of Physicists in Medicine (AAPM) Task
Group 111 Report, “Comprehensive Methodology for the
Evaluation of Radiation Dose in X-Ray Computed Tomography“,
AAPM Task Group 111, February 2010
John A Bauhs et. al.; “CT Dosimetry: Comparison of Measurement
Techniques and Devices”, January 2008 RadioGraphics, 28, 245253
C Ruan et. al.; “Determination of multislice computed tomography
dose index (CTDI) using optically stimulated luminescence
technology”, Med. Phys. 37, 3560 (2010)
Jursinic, P.A.; “Characterization of optically stimulated
luminescent dosimeters, OSLDs, for clinical dosimetric
measurements”, Medical Physics, Vol. 34 (12) December 2007
Yahkne, Ph.D., C.J. , Hanify, R.D., and Salasky, M.R., “Microstar
Calibration Conversion Factors for Dots”, Landauer InLightTM
Systems
American Association of Physicists in Medicine (AAPM) Report
No. 96, “The Measurement, Reporting, and Management of
Radiation Dose in CT”, AAPM Task Group 23, January 2008