single photon nuclear medicine for radiation oncology · single photon nuclear medicine for...

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Single Photon Nuclear Medicine for Radiation Oncology

Richard E. Wendt IIIDepartment of Imaging Physics

5-3250, [email protected]

William D. Erwin, M.S., and Rodolfo Nunez, M.D. contributed slides to this presentation.

Radiopharmaceutical Imaging

• Radioactive tracers label physiology and function.

• Detect presence of specific conditions.

• Measure concentration of specific conditions.

• Measure affinity of locations.

01:50 GMT, 13 January 1998http://www.fourmilab.ch/cgi-bin/uncgi/Earth

Radiopharmaceutical Therapy

• Destructive effect targeted to specific “addresses.”

• Occasional delivery errors.

• Occasional incomplete response.

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Exponential Decay• The essence of decay is that the same fraction of

what remains disappears in a given time interval, whereas a linear decrease would remove the same number each time.

Exponential Decay

0

20

40

60

80

100

120

1 9 17 25 33 41 49 57

Tim e

Am

ount

Rem

aini

ng

Remaining Amount

Linear Decay

0

20

40

60

80

100

120

1 9 17 25 33 41 49 57

Tim e

Amou

nt R

emai

ning

Remaining Amount

Nuclear Reactor

http://web.mit.edu/nrl/www/coreview.html

http://web.mit.edu/nrl/www/core.html

Reactor-Produced RadionuclidesRadionuclide Decay

ModeProduction Reaction Natural Abundance of

Target Isotope (%)σc(b)

14C β- 14N(n,p)14C 99.6 1.8124Na (β-,γ) 23Na(n,γ)24Na 100 0.5332P β- 31P(n,γ)32P

32S(n,p)32P10095.0

0.19—

35S β- 35Cl(n,p)35S 75.5 —42K (β-,γ) 41K(n,γ)42K 6.8 1.251Cr (EC,γ) 50Cr(n,γ)51Cr 4.3 1759Fe (β-,γ) 58Fe(n,γ)59Fe 0.3 1.175Se (EC,γ) 74Se(n,γ)75Se 0.9 30125I (EC,γ) 124Xe(n,γ)125Xe→EC 125I 0.1 110131I (β-,γ) 130Te(n,γ)131Te→

β- 131I 34.5 0.24

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Cyclotron

•

•

r r rF qv B= ×r rF qE=

rmvqB

=

fqB

m=

2πE H R Z A( ) . [ ( ( ) ] /MeV T) cm≈ × −4 8 10 3 2

http://lynx.uio.no/cycdescr.html

Cyclotron ProductionProduct Decay Mode Common Production

ReactionNatural Abundance of

Target Isotope (%)13C β

+ 10B(d,n)11C11B(p,n)11C

19.780.3

13N β+ 12C(d,n)13N 98.9

15O β+ 14N(d,n)15O 99.6

18F β+, EC 20Ne(d,α)18F 90.9

22Na β+, EC 23Na(p,2n)22Na 100

43K (β-, γ) 40Ar(α,p)43K 99.667Ga (EC, γ)

68Zn(p,2n)67Ga 18.6111In (EC, γ) 109Ag(α,2n)111In

111Cd(p,n)111In48.712.8

123I (EC, γ)122Te(d,n)123I124Te(p,3n)123I

2.54.6

201Tl (EC, γ)201Hg(d,2n)201Tl 13.2

Working Generator

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γ Camera: Basic Construction

Collimator

Crystal (sealed)

Photomultiplier Tubes (PMTs)

Radioactive Source of γ or X-rays

Light guide (“pipe”)

(Al faceplates)

(glass window)

light seal

All optical interfaces coupled- coupling grease (Lightpipe-to-PMT)- bonding material (other)

Decoding PMT Output (a.k.a. Anger logic)

LE Williams, Nuclear Medicine Physics, Vol. II, Boca Raton: CRC Press, 1987, p. 113.

Note: original Anger design employed capacitors

Adjusting Linearity

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Linearity Correction

RE Henkin, et al., eds., Nuclear Medicine, St. Louis: Mosby, 1996, p. 91, Fig. 7-7

CFOV

UFOV

Quantitative Flood Evaluation

The Central Field of View (CFOV) has half the area, hence 0.75 the extent on each side, of the Useful Field of View (UFOV).

Uniformity Measures• Calculate for the UFOV and for the CFOV

• Evaluate Differential Uniformity over every vertical and horizontal group of 5 pixels within the chosen FOV

%100minmax

minmaxy UniformitIntegral

FOVFOV

FOVFOV ×+

−=

%100minmax

minmaxy UniformitalDifferenti

pixels 5pixels 5

pixels 5pixels 5 ×+

−=

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Uniformity Measures

IU=3% DU=2%

Collimators

LE Williams, Nuclear Medicine Physics, Vol. II, Boca Raton: CRC Press, 1987, Chapter 4.

Collimator Resolution

RE Hendee, et al., eds., Nuclear Medicine, St. Louis: Mosby, 1996, p. 106, Fig. 8-5.

Note the different terminology from figures from other sources.

zTDFBT

TDRg =++= )(

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Intrinsic Resolution• Intrinsic resolution is the

accuracy of localizing events within the crystal.

• Factors are: crystal thickness, light guide design, PMT technology, and number and size of PMTs.

• Measured without a collimator using a slit phantom

RE Henkin, et al., eds., Nuclear Medicine, St. Louis: Mosby, 1996, p. 89, Fig. 7-4

System Resolution

• The collimator’s geometric resolution (Rg) also plays a role.

• The system resolution (Rs) is the root mean square of the intrinsic (Ri) and collimator resolutions (uncertainty error propagation):

222gis RRR +=

Depth-Independent Sensitivity

• The sensitivity of a parallel hole collimator is roughly independent of depth (F in this figure).

• This is true in a limited field of view

RE Hendee, et al., eds., Nuclear Medicine, St. Louis: Mosby, 1996, p. 104, Fig. 8-4.

Note the different terminology from figures from other sources.

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Gamma Energies and Collimators

Energies of Common NM Gamma Emitters

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 100 200 300 400 500 600

Energy (keV)

Abu

ndan

ce

Co-57 (271.8d)Ga-67 (3.261d)Tc-99m (6.02h)F-18 (110m)Tl-201 (73.1h)In-111 (2.83d)I-131 (8.04d)

Low Energy

Medium Energy

High Energy

511

Single Photon Emission Computed Tomography

Sorenson & Phelps, Physics in Nuclear Medicine, 2nd Ed., Philadelphia: Saunders, 1987, p. 430.

SPECT Cameras

http://www.digirad.com/cardiology.shtm

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SPECT Camera Gantry

Park Medical Systems Brochure, Nov. 1996 Siemens e.cam at U.T. M. D. Anderson Cancer Center

SPECT/CT Gantries

Projections

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Projections

Projections

The Sinogram

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Unfiltered Backprojection

Animation of Unfiltered Backprojection

Spatial Frequencies

Central Slice TheoremImage Magnitude of the FT

Projection

Central Slice

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Density of Samples in the Spatial Frequency Domain

Filtered Projections

Filtered Backprojection

Animation of Filtered Backprojection

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Filters for Backprojection

Z.-H. Cho, J.P. Jones, and M. Singh, Foundations of Medical Imaging, New York: Wiley, 1993, p. 81

Expectation MaximizationChoose an initial

parameter λ[0]. Set k=0.

E-step: Estimate unobserved data using λ[k]

and the measurements y(d).

M-step: Compute maximum likelihood estimate of parameter

λ[k] using estimated data.

k=k+1. Converged?

Done

Typically use FBPas the initial guess.

Estimate the number of counts in each pixel of the projections that came from each pixel of the image.

∑=+

'

][

][]1[

),'(),()(),(

b

k

kk

dbdbdydbx

λλ

Choose the next estimate of λso that it makes the estimated data above most likely.

∑=

++ =D

d

kk dbpdbxb1

]1[]1[ ),(),()(λ

Why is EM Better than FBP?

• The probability function p(b,d) in

• This captures the probability that a count in a particular pixel of the image slice will wind up in a particular point on the projection, which is affected by collimator blurring, attenuation and scatter.

∑=

++ =D

d

kk dbpdbxb1

]1[]1[ ),(),()(λ

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OSEM Iterative SPECT:OSEM Iterative SPECT:Collimator Resolution ModelingCollimator Resolution Modeling

Standard Filtered

Backprojection

2-D Iterativew/ fan beam

modeling (m=12,n=10)

99mTc Bone Scan (osteosarcoma), Low-Energy High-Resolution Collimator

2-D pre-filter: Butterworth, fc = 0.6 Nyquist, order = 10

3-D Gaussian Post-Filter (7.8 mm FWHM)

3-D Iterativew/ cone beam

modeling (m=25,n=10)

OSEM Iterative SPECT:OSEM Iterative SPECT:Collimator Resolution ModelingCollimator Resolution Modeling

Standard Filtered

Backprojection

67Ga Citrate, Medium-Energy Low-Penetration Collimator

3-D Gaussian Post-Filter (9.6 mm FWHM)

12 iterations, 10 subsets

25 iterations, 10 subsets

2-D pre-filter: Butterworth, fc = 0.65 Nyquist, order = 7

2-D Iterativew/ fan beam

modeling

3-D Iterativew/ cone beam

modeling

Acquisition Orbits

Circular

Elliptical

Body

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How Many Views Are Needed?

• Essentially, the azimuthal spacing between lines of projection should equal the spacing between pixels.

• The center is okay, while the periphery needs more views. projectionin spacing pixeld

FOV ofdiameter D where2

180over Views #

==

=dDπo

θ

D

d

Partial Volume Effect

S.R. Cherry, J.A. Sorenson and M.E. Phelps, Physics in Nuclear Medicine: 3rd Ed., Philadelphia: Saunders, 2003, Fig. 17-16

Recovery Coefficient

• The recovery coefficient is the ratio of the apparent concentration to the true concentration.

• Note that RC can be greater than unity when cold spots are present.

S.R. Cherry, J.A. Sorenson and M.E. Phelps, Physics in Nuclear Medicine: 3rd Ed., Philadelphia: Saunders, 2003, Fig. 17-6

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Anterior

Posterolateral

Primary HyperparathyroidismPrimary Hyperparathyroidism

99m99mTc Sestamibi SPECT imagesTc Sestamibi SPECT images



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Uptake in Lumbar SpineUptake in Lumbar Spine



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111111--In ProstascintIn Prostascint

Negative Negative ProstascintProstascint

Attenuation corrected 111Attenuation corrected 111--In Octreotide SPECTIn Octreotide SPECT

Localize Localize NeuroendocrineNeuroendocrine TumorTumor

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CT scan with contrast was equivocal as to pancreas or duodenum.CT scan with contrast was equivocal as to pancreas or duodenum.



Lesion is in the duodenum, not the pancreas.Lesion is in the duodenum, not the pancreas.

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Clearance

0 hrs 6 hrs 24 hrs 48 hrs 120 hrs 144 hrsLogarithmic images, each scaled separately

Region Time-Activity Curve

Simple MIRD

SourceSourceÃ=A0τ

ÃnE

ÃnEφTargetTarget=ÃnEφ/m=ÃΔΦ=ÃS=A0τS

D

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The MIRD Average Man

The Future of Radiopharmaceutical Therapy

• Voxel-scale dosimetry would allow construction of dose-volume histograms.

• Quantitative SPECT is essential in order to determine time-activity curves and cumulated activity for each voxel.

• Registered CT is highly desirable for determining the attenuation properties to feed into radiation transport calculations.

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