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Slides - Department of Physics and Astronomy - University of ...

In vivo Determination of optical

properties from pleural PDT in

humans

Julia Sandell*, Jarod Finlay, Timothy Zhu, Joe Friedberg,

Keith Cengel

Department of Radiation Oncology, University of Pennsylvania

*presenter


Introduction

HPPH Study

Spectroscopic Methods

Optical Properties

Comparison of Optical Properties

Finite Element Modeling (FEM) of fluence

FEM results with inhomogeneous optical

properties and in arbitrary geometries

Conclusion

June 16th, 2010 ASP 2010

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Pleural photodynamic

therapy protocol

Diagnosis: Mesothelioma

or pleural effusion.

Drug: HPPH ® 24 or 48

hrs prior to irradiation.

Light: 661 nm (red) light

15-60 J/cm 2 .

Delivery: Continuously

moving point source in

the thoracic cavity

HPPH Study

June 16th, 2010 ASP 2010

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Spectroscopy

Controller

403-nm Laser

CCD

White light

Multi-fiber probe

Spectrograph

Source 1 1.4 2.7 4.1 6.1 8.1

Sample

Source 2 0.7 2.1 3.5 5.1

June 16th, 2010 ASP 2010

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Fitting two ways to check consistency

Reflectance fitting for wavelength

dependence 1

Reflectance fitting for individual sourcedetector

separations 2

1. Hull & Foster, J. Opt. Soc. Am. 18, 584-599 (2001)

2. Finlay & Foster, Med. Phys. 31,7 (2004)

Absorption model :

µ a

= Σε i

c i

c i

are Hemoglobin and a Gaussian representing HPPH

Scattering model:

µ s´ = A (λ/λ0) -b

⇒Are they consistent with each other?

June 16th, 2010 ASP 2010

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Tissue Optical Properties:

Organ

Aorta

µ a

(cm -1 )

0.12-0.18

Absorption Coefficient: Pre and Post PDT

Pre PDT

Post PDT

Chestwall

0.002-0.54

10

Diaphragm

0.15-1.08

Lung

0.49-0.88

1

Pericardium

Serratus

Skin

0.07-0.79

0.17-0.97

0.51-0.64

m_a (cm^-1)

0.1

0.01

Organ

µ s

’(cm -1 )

Aorta

Chestwall

Diaphragm

31.20-1120

2.91-19.45

9.65-21.7

0.001

aorta

chestwall

chestwall

diaphraghm

diaphragm

lung

lung

lung

pericardium

pericardium

Organ

seratus

serratus

serratus

serratus

skin

skin

tumor

Lung

21.14-22.52

Pericardium

25.68-51.61

* Log scale

Serratus

3.875-38.0

Skin

2.24-5.77

June 16th, 2010 ASP 2010

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Comparison of Optical Properties

Pre-PDT: Wavelength and Soure-Detector Separation

Wavelength Fit

Source-Detector Fit

10

mueff

1

aorta

aorta

aorta

chestwall

lung

lung

lung

pericardium

pericardium

pericardium

pericardium

pleura

Organ

* Log scale

June 16th, 2010 ASP 2010

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Summary of Two Fitting Methods

Generally the source-detector fit provides higher values

for µ eff than those given by wavelength fitting

Differences in optical properties are overall within an

order of magnitude

Future work will include a phantom study to be able to

determine in a systematic way how the two methods

differ

From this study we hope to develop constraints on the

algorithms

June 16th, 2010 ASP 2010

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Finite Element Modeling (FEM)

Standard diffusion equation solution

Assume homogeneous optical properties

Computing fluence in cavity walls

Using Comsol Multiphysics software®

Agrees with analytical solution of fluence

June 16th, 2010 ASP 2010

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Analytical Solution:

Fluence in tissue surrounding a cavity

Solving the diffusion equation in a cavity setting:

Must account for multiple scattering within cavity

Fluence outside cavity is independent of index of

refraction mismatch

S=source (W)

$

t

=

3S

"[

µ

4#

tr

! µ

eff

e

r(1

+ µ

( r!

r

eff

c

)

" r

c

)

!

2e

! µ ( r!

r

r

t

2

c

)

]

µ tr

= µ a

+ µ s


µ eff

= (3µ a

µ s

’) 1/2

r = distance away

from source

rc = radius of cavity

°Star, WM, PMB 40, 1-8 (1995)

June 16th, 2010 ASP 2010

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FEM Results:

Spherical Cavity with a Centrally Located Source

Fluence rate calculated

using optical properties

from study

Modeling the fluence rate

in the tissue surrounding a

spherical cavity

Cavity radius determined

from volume data of each

patient

Power ranges from 5-8 W,

according to treatment

June 16th, 2010 ASP 2010

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FEM Solution:

Spherical Cavity with Inhomogeneous Optical

Properties

Using a linear function to

describe µ a

Varying this function over

180°

Definite change in fluence

in half of cavity where µ a is

varying

Allows us to set up different

regions of optical property

values

Agrees with analytical

solution

June 16th, 2010 ASP 2010

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FEM Solution:

Contours from Chest Phantom

Assume homogeneous

optical properties

Centrally located source

Read in data from a

chest phantom to

generate contours

Compute fluence within

arbitrary geometry in

surrounding tissue

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Conclusion

General agreement in optical properties between

source-detector and wavelength fitting

Able to use FEM to model effects on fluence

from heterogeneous optical properties

Determine fluence of surrounding tissue using

FEM in arbitrary geometries

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Future Work

Use IR camera system to

obtain patient geometry

during surgery

Develop a FEM solution

for arbitrary source

location and fluence

within the cavity

Account for the effect of

heterogeneous tissue

optical properties on

fluence using FEM

6

5

m 4

c

2 / )

J

3

(

2

!

1

0

-20

-25

Z (cm)

-30

-35

-40

-30

-20

-10

Y (cm)

0

June 16th, 2010 ASP 2010

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Acknowledgements





Support

NIH R01-CA-129554 (T. Busch)

ACS IRG-78-002-28 (J. Finlay)

Theresa M. Busch, Ph.D.

PDT Program

Clinicians: Harry Quon; ; Kelly Malloy; Bert O’Malley, O

Jr; ; Gregory Weinstein

Physicists: Timothy Zhu; Jarod Finlay; Andrea Dimofte, , Chang Chang, Ken Wang

Carmen Rodriguez, Deborah Smith, Michael Mehler

Travel Funding

Fontaine Foundation

Graduate and Professional Student Association

Thank you!

June 16th, 2010 ASP 2010

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