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

[email protected]

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

2

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

7

Nano Technology Overview

8

• Radiation interacts with nano-material to generate optical

photons

• Optical photons are measured at photo-detector

9

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

10

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

11

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

12

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

14

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

15

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

16

•All students interested in

pursuing MS and PhD degree

programs are encouraged to

contact me or my students.

17

Topics

1. Introduction of DRDL

2. Lens of the eye dose in pediatric

CT

18

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

20

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

22

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

25

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


26


• 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


27


• 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


28


• 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


29


• 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


30


• Phantoms: CIRS Anthropomorphic Phantoms

• Dosimeters: MOSFETs

• CT Scanners: • Siemens SOMATOM Definition

Flash

• GE Discovery 750 HD SIEMENS

GE

Methods and Materials


31


• 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


32


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


33


• 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




34

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




36

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


37


• 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


38


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


39


• 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


40


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


41


• 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


42





(OB-TCM)


Lens dose

reduction

methods


Organ-Based Tube Current Modulation

(OB-TCM)


43


Physics Part 2. - Conclusions


44


• 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


45





(OB-TCM)


Lens dose

reduction

methods


Gantry Angulation in Head CT


46


Lens

Physics Part 3- Conclusions


47


• 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


48


•Clinical Component

1. Pediatric Patient Study

2. Adult Patient Study

Retrospective Patient Study


49


• IRB approved

retrospective study

• Initially, there were

over 10,000

(pediatric) and

70,000 (adult)

head CTs between

2009-2013

Retrospective Patient Study


50


• 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


51


• 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


52


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


53


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


54


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


55


• 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


56


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


57


• 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


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


59


• 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!

60

nc hps fall meeting october 6, 2016 unc chapel hill, nc

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