NC HPS FALL MEETING October 6, 2016 UNC Chapel Hill, NC
Transcript of NC HPS FALL MEETING October 6, 2016 UNC Chapel Hill, NC
INTRODUCING DUKE RADIATION DOSIMETRY LABORATORY
AND REPORT ON CURRENT RESEARCH
Terry Yoshizumi
Duke Radiation Dosimetry Laboratory
(DRDL)
Duke University Medical Center
NC HPS FALL MEETING
October 6, 2016
UNC Chapel Hill, NC
Acknowledgements
Research team
• Giao Nguyen, MS, Lab Manager, Yoshizumi Lab
• Dr. Gunasingha, Director, Gunasingha Lab (Monte Carlo
Computational Dosimetry Lab)
• Natalie Januzis, PhD
• Past and present students
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Topics
1. Introduction of DRDL
2. Lens of the eye dose in pediatric
CT
3
DRDL Organizational Structure (2016)
4
DRDL
Yoshizumi
Lab
Gunasingha
Lab
Organization
Unique features
• Resources from Radiation Safety Office and Duke
Radiation Dosimetry Laboratory (DRDL)
• Faculty level expertise and graduate students
5
DRDL History
TLD program for organ dose Measurements
In radiology
2000 2002 2005
1st generation
of MOSFET
2003
2nd generation
of MOSFET
3rd generation
of MOSFET Mobile MOSFET
6
2009
Radiochromic Film
dosimetry
2011-12
Nano Particle detector
~17 cm
Mouse
phantom
2016-2017
Research focus: • Patient dosimetry • Small animal dosimetry • Nano detector development HP education focus: • Minority recruitment • Undergraduate summer internship
RESEARCH AREAS
1. Real-time fiber-optic dosimeter technology
• Neutron application and proton therapy dosimetry
2. Small animal dosimetry (radiation biology)
• Physics challenges in dosimetry accuracy
• Monte Carlo simulations
3. Patient dose monitoring
• Imaging dose monitoring (CT, CC, IR, etc)
• Radiation therapy patient dosimetry
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Nano Technology Overview
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• Radiation interacts with nano-material to generate optical
photons
• Optical photons are measured at photo-detector
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Nano-Fiber Optic Detector (nano-FOD)
Technology Overview
• The nanoFOD device:
• novel nanomaterial
• Linear scintillation with
ionizing radiation
• Nanomaterial coupled to
optic fiber & photodiode
• Current from diode:
• converted to dose
• displayed in real time.
Radiation
2. Optical
Fiber
Photo-Detector
and data board
1. Nanocrystal tip
nanoFOD
Small animal nano-FOD application
• MP paper – Farrington Daniels Award AAPM 2016
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Nano-
FOD
(Gy)
Presage
(Gy)
%
differenc
e
9.49 9.23 2.8
Nano-sensor consortium 2013-2016
Mike Therien
Oana Craciunescu Radiation Oncology
Chino, Therien, Yoshizumi
Nano-detector program
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UNC PHYSICS UNC Rad Onc
NCSU NUCLEAR ENG
MIT
KEY DRDL COLLABORATORS – PAST AND PRESENT
WAKE FOREST
Sha Chung Julian Down Mohamed Bourham
ALCORN STATE
J. Daniel Bourland Jermiah Kiran Billa
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Health Physics Program Overview
13
HP student
enrollment
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
MS 2 2 4 4 4 7 9 7 3 2 1
PhD 2 2 2 2 3 3 4
2016
1
2
Health Physics Program Overview
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2005 - 2016 total Minority (%)
MS degrees in HP 15 2 (13%)
PhD degrees in HP 5 0 (0%)
2005 - 2016 total
MS enrollment in
HP 16
PhD enrollment in
HP 7
RECENT GRADUATES AND CURRENT STUDENTS
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Chu Wang, PhD, May 2016
HPS Fellowship; DRDL Fellowship
Univ. of Pittsburgh
Natalie Januzis, PhD May 2016
NRC HP Fellowship
Univ of Pennsylvania
Matt Belley, PhD, May 2016
NRC HP Fellowship
Brown University
Bria Morre, BS
PhD Student
Dean's graduate fellowship
DRDL Fellowship, NRC Fellowship
HPS Robert Gardner Fellowship
Justin Raudabaugh, MS
PhD student,
DRDL Fellowship
NRC Fellowship
Aaron Smith, BS
MS student, NRC Fellowship
Funding sources
• NRC GRANT
• NASA GRANT
• NIH GRANT
• BME Coulter Grant
• INDUSTRY GRANT (Siemens, Philips, GE)
• FELLOWSHIP OPPORTUNITIES • DOE
• NRC
• US AIRFORCE
• AAPM
• HPS
• DUKE UNIVERSITY
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•All students interested in
pursuing MS and PhD degree
programs are encouraged to
contact me or my students.
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Topics
1. Introduction of DRDL
2. Lens of the eye dose in pediatric
CT
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Radiation Dose to the Lens of the Eye from
Computed Tomography Scans of the Head
October 6, 2016
Chapel Hill, NC
Natalie Januzis, Terry Yoshizumi*
Topics
1. Introduction
2. Physics Component
Estimating lens dose from CTDIvol
Organ-based tube current modulation
Gantry angulation
3. Clinical Component
Pediatric patient study
Adult patient study
4. Concluding remarks
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skip
Motivation 1
• AJR cataract paper review in 2012
• Weaknesses
• No lens dose data; instead used the number of CT scans
21 Introduction Physics Component Clinical Component Conclusions
Radiation-induced Cataract • Lens is an avascular tissue with an
epithelial cell layer containing lens
fibre cell progenitors on the anterior
surface
• Types of cataract:
• Cortical, nuclear, posterior
subcapsular, and supranuclear
• Posterior Subcapsular Cataract (PSC)
associated with radiation exposure
Background and Significance
Worgul et al., “Cataracts among Chernobyl Clean-up Workers: Implications Regarding Permissible Eye Exposures,”
Radiation Research 167: 233-243 (2007).
Lens Anatomy
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Cataract Incidence and Treatment
• Leading cause of blindness worldwide
• Lens opacities found in 96% of the population
over 60 years old
• Only treatment is surgical removal • Accounts for 12% of US Medicare budget overall and 60% of all
Medicare costs related to vision
• Cataract costs represent 40% of overall US ocular disease
expenditures
• Risks associated with treatment:
• Posterior capsular opacification (secondary cataract), raised intraocular pressure,
retinal detachment, etc.
Background and Significance 23
• Radiation-induced cataracts in humans first reported in 1906
• Dose thresholds estimated using data on exposed populations
Radiation Exposure and Cataracts
Decreasing
dose
threshold
Problems with older studies:
– Few subjects with doses < few Gy
– Did not have tests sensitive enough to detect early lens changes
Kleiman, NJ, “Radiation Cataract,” Annals of the ICRP 41: 80-97 (2012).
Background and Significance 24
Lens Dosimetry Model
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Introduction - Physics Component - Clinical Component - Conclusions
• Physics Component
Part 1. Estimating lens dose from CTDIvol
Part 2. Organ-based tube current modulation
(OB-TCM)
Part 3. Gantry angulation
Lens dose
reduction
methods
Introduction Physics Component Clinical Component Conclusions
Challenges with Lens Dosimetry in Head CT
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• Variety of different head imaging protocols
• Each with different technical parameters (mA, pitch, etc.) based on anatomy to be imaged
Brain Sinus Facial Bones
Orbits Craniofacial
All of Siemens protocols were helical. For GE, the craniofacial protocol was the only one acquired helically.
Estimating Lens Dose in Head CT Exams
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• Approach • Determine a lens dose estimation method that does not
require knowledge of protocol-specific exposure factors (kVp, mA, etc.)
Lens dose measured in
anthropomorphic
phantoms
CTDIvol-
to-lens
dose CF
Standard measure of
scanner radiation output
(CTDIvol)
Estimating Lens Dose from CTDIvol
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• Volume CT Dose Index (CTDIvol) • Represents the weighted average
radiation dose within a cylindrical phantom from a central slice of a scan
A
B
C
D
E
CTDI Head phantom:
• Diameter: 16 cm
• Material: PMMA
• A-E: pencil ion chamber
openings
• A: Center
• B-E: Peripheral – 1 cm
from surface
Estimating Lens Dose from CTDIvol
Introduction Physics Component Clinical Component Conclusions
29
Introduction - Physics Component - Clinical Component - Conclusions
• Advantages of
using CTDIvol
• Accounts for
differences in technical
parameters (mA, kV,
pitch, etc.) among
different imaging
protocols
• Recorded in a
patient’s medical
record for each exam
Methods and Materials
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• Phantoms: CIRS Anthropomorphic Phantoms
• Dosimeters: MOSFETs
• CT Scanners: • Siemens SOMATOM Definition
Flash
• GE Discovery 750 HD SIEMENS
GE
Methods and Materials
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• One MOSFET dosimeter placed in
predrilled location for lens of the
eye
• MOSFETs calibrated at 120 kV
against an ADCL calibrated ion
chamber
• Phantoms scanned with 5 different
imaging protocols on each
scanner:
• Brain, Sinus, Facial Bones, Orbits,
Craniofacial
Phantom- and Protocol- Specific Lens
Dose
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
Brain Sinus Facial Bones Orbits Craniofacial Craniofacial
HD
Le
ns
do
se
(m
Gy
)
Newborn
1-year-old
5-year-old
10-year-old
Adult female
Adult male
GE Discovery 750 HD
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
Brain Sinus Facial Bones Orbits Craniofacial
Le
ns
do
se
(m
Gy
)
Newborn
1-year-old
5-year-old
10-year-old
Adult female
Adult male
SIEMENS SOMATOM Definition Flash
Phantom age-specific CTDIvol-to-lens
dose conversion factors
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• CTDIvol was recorded off of
the structured dose report
• Linear regression analysis
was performed to derive
phantom age-specific CFs
• Scanner-specific
• Scanner-independent
Slope of the line is taken as
the CTDIvol-to-lens dose CF
Phantom age-specific CTDIvol-to-lens
dose conversion factors
Introduction Physics Component Clinical Component Conclusions
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Phantom
Discovery 750 HD
SOMATOM
Definition Flash
Scanner-
independent
CF R2 CF R2 CF R2
Newborn 1.18 0.96 1.07 0.99 1.14 0.94
1-year-old 1.01 0.99 0.97 0.96 0.99 0.97
5-year-old 0.93 0.95 0.95 0.99 0.94 0.97
10-year-old 0.88 0.94 0.85 0.98 0.86 0.95
Adult female 0.86 0.96 0.82 0.94 0.84 0.94
Adult male 0.88 0.90 0.84 0.90 0.86 0.89
Decreasing CTDIvol-to-lens
dose CF with increasing age
Motivation 2
• ICRP Publication 118 (2012):
• Reduced threshold dose to 0.5 Gy (50 rads)
• Previous threshold dose estimates were
0.5-2 Gy for acute and 5 Gy for protracted
exposures
35 Introduction Physics Component Clinical Component Conclusions
Phantom age-specific CTDIvol-to-lens
dose conversion factors
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions Newborn 1-year-old 5-year-old
10-year-old Adult
female
Adult
male
CTDI phantom
16 cm
10 cm 13 cm 14 cm
15 cm 16 cm 17 cm Normalizing dose in
phantoms of varying sizes
to dose measured in a 16-
cm diameter phantom
Due to the effects of
attenuation, lens dose
(and CTDIvol-to-lens dose
CFs) will vary among
head sizes
Patient Size-Specific Mathematical Model
Between Lens Dose and CTDIvol
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• AP and lateral (LAT) measurements were used to
calculate the effective diameter, dEff
• Phantom age-specific CTDIvol-to-lens dose CFs were
plotted against dEff and exponential regression analysis
was performed to derive α and β
Patient Size-Specific Model to Estimate
Lens Dose from CTDIvol
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
Effective Diameter, dEff
(cm)10 11 12 13 14 15 16 17 18
CT
DI v
ol-t
o-L
en
s D
os
e C
F
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
R2: 0.962
Eqn: 1.870exp(-0.048dEff
)
Scanner Independent (SI)
Exponential regression
coefficients
α β R2
Discovery 750 HD 2.005 -0.051 0.95
SOMATOM Definition Flash 1.667 -0.041 0.92
Scanner-independent (SI) 1.870 -0.048 0.96
Evaluation of Patient Size-Specific
Mathematical Model
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• Determined the CTDIvol-to-lens dose CF for each
phantom using their effective diameter measurement and
the SI fit function
• Calculated the lens doses for each phantom and protocol
from the CTDIvol
• Compared fitted and measured values:
Evaluation of Patient Size-Specific
Mathematical Model
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
0 10 20 30 40 50-30
-20
-10
0
10
20
30
CTDIvol (mGy)Dif
fere
nce
betw
een
fitt
ed
an
dm
easu
red
(%)
-21
-18
-15
-12 -9 -6 -3 0 3 6 9 12 15 18 21
0
5
10
15
Difference between fitted and measured (%)
Nu
mb
er
of
valu
es
• 84% of fitted values fell within 10% of measured values
• 97% of fitted values fell within 15% of measured values
Physics Part 1.- Conclusions
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• Lens dose per protocol ranged from 4-36 mGy
• Derived a scanner-independent, size-specific
method to estimate lens dose from CTDIvol
• Fitted values fell within 10-15% of measured values
Lens Dosimetry Model
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Introduction - Physics Component - Clinical Component - Conclusions
• Physics Component
Part 1. Estimating lens dose from CTDIvol
Part 2. Organ-based tube current modulation
(OB-TCM)
Part 3. Gantry angulation
Lens dose
reduction
methods
Introduction Physics Component Clinical Component Conclusions
Organ-Based Tube Current Modulation
(OB-TCM)
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
Physics Part 2. - Conclusions
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• Lens dose per protocol ranged from 5-25 mGy
• Average reduction in dose with OB-TCM ranged
from 14-26%
• Larger error associated with OB-TCM in CTDIvol-
to-lens dose estimation method
• Stresses the need for accurate positioning when using
this dose reduction method
Lens Dosimetry Model
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Introduction - Physics Component - Clinical Component - Conclusions
• Physics Component
Part 1. Estimating lens dose from CTDIvol
Part 2. Organ-based tube current modulation
(OB-TCM)
Part 3. Gantry angulation
Lens dose
reduction
methods
Introduction Physics Component Clinical Component Conclusions
Gantry Angulation in Head CT
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
Lens
Physics Part 3- Conclusions
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• Dose to the orbit can decrease by 67-92% with gantry angulation
• Effectiveness of this method to reduce lens dose is dependent upon the anatomy of the head • Influences whether or not entire brain can be scanned
while still avoiding the orbit
• Dose to the lens depends upon the distance from the imaged volume
Patient Lens Dose Reconstruction
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
•Clinical Component
1. Pediatric Patient Study
2. Adult Patient Study
Retrospective Patient Study
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• IRB approved
retrospective study
• Initially, there were
over 10,000
(pediatric) and
70,000 (adult)
head CTs between
2009-2013
Retrospective Patient Study
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• 206 pediatric patients and 243 adult patients were
selected for chart review
• MaestroCare application was used to access electronic
medical records
• For each exam, CTDIvol was recorded off of structured
dose report
• AP and LAT diameters were measured on axial images in
the supraorbital region
Lens Dose Reconstruction Methods
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• AP and LAT diameters on axial images were used to
calculate effective diameter
• Use effective diameter to determine CTDIvol-to-lens dose
CF
Scanner-independent OB-TCM
** Requires knowledge of scanner model/manufacturer**
Lens Dose Reconstruction Methods
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
Room 2009 2010 2011 2012 2013
B5 GE Lightspeed GE Lightspeed GE Lightspeed Siemens Definition
Flash
Siemens Definition
Flash
C1 GE VCT Siemens
Definition
Siemens Definition Siemens Definition
Flash
Siemens Definition
Flash
C3 GE Lightspeed GE Lightspeed GE Lightspeed GE Discovery 750
HD
GE Discovery 750
HD
J1 GE Lightspeed
XTRA
GE Lightspeed
XTRA
GE Lightspeed
XTRA
GE Lightspeed GE Lightspeed
J3 GE Lightspeed GE Lightspeed GE Lightspeed GE Lightspeed GE Lightspeed
CTER_1 GE VCT GE VCT GE VCT GE Lightspeed GE Lightspeed
CTER_2 - - GE VCT GE Lightspeed GE Lightspeed
CTS_3 - - GE Discovery 750
HD
- -
PO - Neurologica
Ceretom
- - -
** Assumed OB-TCM was employed on all head scans performed on Siemens
scanners starting in 2010 **
Relationship Between Head Size and Age
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
0 2 4 6 8 10 12 14 16 185
10
15
20
Age (years)
Eff
ecti
ve
dia
mete
r,d
Eff
(cm
)
20 25 30 35 40 45 50 55 60 65
12
14
16
18
20
22
Age (years)
Eff
ecti
ve
dia
mete
r,d
Eff
(cm
)
Pediatric Adult
Cumulative Lens Dose
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
Pediatric Adult
50 550 1050 1550 2050 2550 30500
20
40
60
Cumulative lens dose (mGy) from 2009-2013
Nu
mb
er
of
pati
en
ts
0 100 200 300 400 500 600 700 800 900 10000
10
20
30
40
50
Cumulative lens dose (mGy) from 2009-2013
Nu
mb
er
of
pati
en
ts
ICRP Threshold Dose (500 mGy) ICRP Threshold Dose (500 mGy)
17 patients
(8.3%)
53 patients
(22%)
Age-Based vs. Size-Based Cumulative Lens Dose
Introduction Physics Component Clinical Component Conclusions
55
Introduction - Physics Component - Clinical Component - Conclusions
• Evaluate the need for patient size estimates when
estimating lens dose from CTDIvol
• Calculated lens dose using the phantom age-
specific CTDIvol-to-lens dose CFs
Patient Age
(years)
Phantom age-
specific CF
0-1 Newborn
1-5 1-year-old
5-10 5-year-old
10-18 10-year-old
18+ Adult male
Age-Based vs. Size-Based Cumulative
Lens Dose
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
Pediatric Adult
0 1000 2000 3000 4000
0
1000
2000
3000
4000
Age-based lens dose (mGy)S
ize-b
ased
len
sd
ose
(mG
y)
y = 0.9415x
R2 = 0.9934
0 500 1000 1500
0
500
1000
1500
Age-based lens dose (mGy)
Siz
e-b
ased
len
sd
ose
(mG
y)
y = 0.9777x
R2 = 0.9884
Age-based overestimates lens dose compared to size-based
Clinical– Conclusions
Introduction Physics Component Clinical Component Conclusions
57
Introduction - Physics Component - Clinical Component - Conclusions
• Reconstructed cumulative lens doses from head
CT exams
• Pediatric: 40-1016 mGy
• Adult: 53-2892 mGy
• ** Important to note that Duke is a Level I Trauma
Center and has a comprehensive cancer center
**
• Distribution of lens doses may be different than other
medical centers
Re-cap
Introduction Physics Component Clinical Component Conclusions
58
Physics Component
Clinical Component
• Derived a model to estimate lens dose from CTDIvol
• Determined methods to account for lens dose reduction methods • OB-TCM
• Gantry angulation
• Reconstructed patient
doses • Pediatric
• Adult
Concluding remarks
Introduction Physics Component Clinical Component Conclusions
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Introduction - Physics Component - Clinical Component - Conclusions
• New dosimetry model may be used for future epidemiological
studies in CT
• Cumulative lens dose in pediatric patients may present potential
risks; Cataracts in growing children are more clinically challenging
than adults
• Nation-wide surveys report 69%* of all 309,807 pediatric scans
were head (lens dose may be of concern?)
• At Duke we found that pediatric head CT scans were 58% of total
5239 CT scans in 2003 and 45% of total 4852 in 2015.
• A follow-up study for patients with lens dose > 0.5 Gy may shed
new light on the cataract incidents and threshold dose
• A larger scale pediatric CT lens dose study may shed more light.
*Don Frush
Thank you!
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