INT EXPERIENCE IN VOXEL DOSIMETRY FOR 90-Y MICROSPHERES LIVER

TREATMENT PLANNING

C. Chiesa, Foundation IRCCS Istituto Nazionale Tumori MILAN

Anna Negri, Post graduate Health Physics school

Silvia Pellizzari, Facoltà di Ingegneria, “la Sapienza” University , Rome

Index • Aim of our study • Quantitative single

SPECT • Voxel quantification • Is convolution necessary

? • Multiple SPECT approach • Clinical application: 90Y

microsphere dosimetry

• VOXELDOSE by A. Dieudonnè

• STRATOS by PHILIPS

AIM OF OUR STUDY

For a parallel organ, and a fixed mean dose non uniformity reduces biological effects

0

50

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Gy

REAL

volume 1volume 2

0

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MEAN APPROX

volume 1volume 2

Overkilling

Reduced biological effect Apparently good biological effect

120 Gy SF = 9%

O’Donoghue Implications of Nonuniform Tumor Doses for

radioimmunotherapy: Equivalent Uniform Dose JNM 1999 40:1337-1341

• BED →ψ (distribution)

• Sf (ψ) dψ = p(ψ) dψ exp(-αψ)

• SF = ∫ p(ψ) dψ exp(-αψ)

• EU_BED = -1/α ln(SF)

• It is BED which wuold give same biological effect (SF) if BED distribution was uniform

BED normalised distribution

0,0E+00

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Gy

prob

abili

ty

40 0,2

BED-VH differenziale

EUD - EU_BED in voxel dosimetry

⋅−=

∑ ⋅−

voxel

i

BED

n

eBEDEU

iα

αln1_

DeSF ⋅−= α

BEDeSF ⋅−= α

⋅−=

∑ ⋅−

voxel

i

D

n

eEUD

iα

αln1

Global survival fraction is the average

of survival fraction in single voxels

β=0

β≠0

AIM In liver radioembolization

which parameter better correlates with biological effects ? (if any)

Jones LC, Hoban PW

Treatment plan comparison using equivalent uniform biologically effective dose EU_BED Phys Med Biol (2000) 42:159-170

Non uniformity effects NEGLECTED

(mean voxel quantities)

Non uniformity effects INCLUDED

Dose rate effects NEGLECTED Mean dose D EUD

Dose rate effects INCLUDED Mean voxel BED EU_BED

Is it possible to outline a treatment planning based on dosimetric strategy ?

EUD explains lobar treatment limited toxicity (linear model, β=0 for simplicity)

Survival fraction for lobar treatment

(hp spared lobe fraction = 0.3)

SF = 0.7 exp(- α D) + 0.3

0.10

1.000 50 100 150 200 250 300

Mean absorbed dose to whole liver D (Gy)

SF

0.3

EUD = -1 / α * ln(SF)

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Mean absorbed dose to whole liver D (Gy)

EUD

(Gy)

1st Effect of non uniformity, at lobe scale

Quantitative single SPECT

• Two identical spheres with identical 99mTc activity positioned at the centre and at the border of a 20 cm cylindical water phantoms

• The apparent difference in counts is evident • In principle, attenuation effects are reduced for high energy (131-I) • In practice, effective linear attenuaiton coefficients are similar • WE DO NEED ATTENUATION CORRECTION

Quantification: need of attenuation correction

SPECT ATTENUATION CORRECTION METHODS SPET-CT or PET-CT (124 I, 90Y) are ideal. CT attenuation rescaled for gamma energy . SPECT and CT from different scanner: mispositioning, DICOM compatibility problems (feasible since mu map is rather flattened, especially in abdomen) Chang attenuation correction: OK if medium is uniform (brain). Poor on abdomen, forbidden in thorax.

Scaled to 140 keV

Scaled to 140 keV

Our voxel dosimetry workflow CT Siemens 5 mm slices SPET GE Infinia 4.42 mm slices

Siemens e.soft work station

SPECT – CT coregistration: patient mispositioning problem

OSEM reconstruction: DICOM compatibility problem (unsolved)

CT based attenuation correction (GE requires a SPECT-CT gantry)

Scatter correction (no a INT)

PSF correction (no a INT)

MATLAB SPECT convolution code on PC. Radiobiological calculation.

Attenuation corrected SPET

Mispositioning partially corrected by coregistration.

Major problem for organ delimitation: having only SPECT on MATLAB.

Lost the anatomical reference of CT

Sensitivity calibration (counts to activity conversion)

Patient relative • Possible if the known

injected activit is within the FOV

• Ex: microsphere

Absolute • Necessary in

systemic administration

• Preliminar phantom calibration

totalGBqActivityvoxelGBqActivity

totalmTcCountsvoxelmTcCounts

)()(

)99()99(

=

Tumor volume < 1 cc were considered non reliable 99mTC SPECT dosimetric calculations

Strong limit with 131-I voxel dosimetry

Recovery coefficient as a function of sphere volume

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1.40

0 5 10 15 20 25 30Volume [cm^3]

R

Recovery Cooefficient

Partial volume effect correction is possible and mandatory in mean dose approach

It is not applicable for voxel approach

When is voxel dosimetry useful ?

• Voxel dosimetry is useful if activity appears non uniform at voxel level, to use EUBED model

• It is less useful when activity distribution appears uniform

• Is must be corrected when the

medium is NON uniform “Appears” : we do not see the real

activity distribution

177Lu DOTATATE: rather uniform

99mTc-MAA liver radioembolization

Dosimetric optimization of SPECT OS-EM reconstruction protocol

Mean dose is not disturbed by image noise Single voxel counts are strongly affected by image noise. High spatial resolution is important. WE STUDIED: • Spatial resolution • Uniformity & statistical noise (Strongly impacts on single voxel counts ! ) • Uniformity in a single lesion (Strongly impacts single voxel counts ! ) •Partial volume effect (Non trivial on single voxel basis, non isotropic)

Spatial resolution vs subsets and iteration number

9.8

13.2

8.4

11.6

7.0

11.3

6.6

11.0

6.5

10.3

6.9

10.0

6.6

10.1

6.1

9.9

6.8

10.3

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3

6

9

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15

0 8.4Gaussian filter [mm]

Spat

ial r

eolu

tion

FWH

M [m

m]

4 subs 4 it6 subs 6 it8 subs 8 it10 subs 10 it6 subs 30 it10 subs 20 it10 subs 30 it15 subs 30 it30 subs 30 it

Apparent dose distribution (Differential DVH) depends on image NOISE which depends on image statistics & the recon parameters

4 subs 4 it 10 subs 10 it 30 subs 30 it

Noise dependence upon recon parameters and filtering

2.1% 2.0%2.9%

2.3%

3.8%

2.4%

5.3%

3.4%

7.2%

4.0%

7.7%

4.2%

9.7%

4.7%

12.4%

5.3%6.3%

19.4%

0%

5%

10%

15%

20%

0 8.4

Gaussian filter FWHM [mm]

(Dev

. St.)

/ mea

n [%

]

4 subs 4 it6 subs 6 it8 subs 8 it10 subs 10 it6 subs 30 it10 subs 20 it10 subs 30 it15 subs 30 it30 subs 30 it

Sphere in background 4:1 phantom: dosimetry of a sphere 37 mm in diameter α= 0.2/Gy , no gaussian filter ROI threshold choice in order to reproduce the volume Uniform sphere: D = EUD theoretically ∆ between them increases with noise We choose a resonable compromise between ∆ and spatial resolution

Recon par V D EUD ∆ α = 0,2 /Gy [cm³] [Gy] [Gy] [%]

4 subs 4 it 27,5 289 230 20,6% 6 subs 6 it 28,0 300 225 25,1% 8 subs 8 it 27,8 306 227 25,8%

10 subs 10 it 27,6 308 212 31,0% 6 subs 30 it 28,1 307 207 32,7%

10 subs 20 it 27,5 309 210 32,1% 10 subs 30 it 27,0 310 210 32,1% 15 subs 30 it 28,7 304 204 32,8% 30 subs 30 it 27,0 322 211 34,4%

Voxel dosimetry: convolution

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0.5

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SPET image:

One single cubic voxel

is radioactive (4.42 mm)

90-Y Dose image:

Energy is transported

to neighbour cubic voxels

This calculation has to be repeated for any source voxel

(million of voxels)

Massimiliano Pacilio (Roma) Nico Lanconelli, Sergio Lo Meo (Bologna) Leonel Torres; Marco Coca Perez (Cuba) Francesca Botta, Marta Cremonesi, Amalia Di Dia, Mahila Ferrari (IEO Milano)

S-factors for different Voxel Dimensions & Radionuclides

San Camillo Forlanini Hospital - Roma Alma Mater Studiorum - Bologna University Center for Clinical Research, Havana - Cuba

European Institute of Oncology - Milano Courtesy of Francesca Botta, IEO, Milan Italy

www.df.unibo.it/medphys

S values depende DRAMATICALLY on distance on source voxel

β irradiation: nearest neighbour has 1/10 dose of the source voxel

X irradiation (bremstrahlung)

Energy trasport: how far ? CONCEPTUAL PROBLEM 90Y • Rmax: 11 mm • Rmean 4 mm • INT 4.4 mm voxel: 11 voxel

kernel • Cesena 4.8 mm voxel: 5 voxel

kernel • M. Ljungberg (Lund): 1 voxel

kernel. Local deposition.

PRACTICAL PROBLEM • Convolution enlarges the object • Voxel are populated, but they do

not belong to patient body

OK

NOT OK

• With liver treatment and beta emitters, propagation goes not far

• We use a second threshold on dose (unsatisfactory approach)

• With gamma emmitters, and systemic administrations, out body voxel are populated

• Each region under study should be segmented (time consuming)

Energy trasport: how far ?

Convolution seems not necessary for β emission Ljungberg Frey Sjogreen Liu Dewaraja Strand Canc Biother & Radiopharm 2003:18 99-107

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0 1 2 3 4 5 6 7 8 9 10

mm

S (G

y / G

Bq s

)

S - Voxel transport

PSF - 7 mm spatialresolution

Convolution seems not necessary for β emission

• The spatial resolution is a propagation of counts out of the source voxel • Dose transport is an additional propagation on image to be avoided • Approximation: dose is proportional to voxel count, without voxel convolution

• Dvoxel = Ãvoxel S or Dvoxel = NDs S

• S = Dvoxel / NDs = <Eβ> / Mvoxel NDs / NDs = <Eβ> / Mvoxel = 933 keV / Mvoxel

• S = 1.729 Gy / (GBq s) (voxel side 4.42 mm)

• In particular, with microsphere

• Ãvoxel = Avoxel / λ = ALIVERCvoxel (Tc) / CLIVER (Tc) / λ only physical decay

• Dvoxel = Cvoxel (99m-Tc) [1.443 x 64.2 x 3600 x ALIVER [GBq] / CLIVER (Tc) x 1.729 ]

• Dvoxel = Cvoxel (99m-Tc) x K

• Advantage: rescaling the SPECT allows to use of all work station softwares, SPECT-CT coregistration, counturing on coregistered images, ROIS, ROI statistics…..

• Problem with mantissa if Gy unit is used: K = 0.03518 Gy • We used cGi • Limit of 2 byte integer. Siemens station cuts above.

• Organ dosimetry is immediate with Olinda also for gamma emitters. You

take only the photon column from the output

• For lesions, gamma S values are needed. (Gamma contribution is low anyhow).

Convolution seems not needed for β emission

CALCOLO DOSE VOXEL SENZA CONVOLUZIONE Limite 2 byte 65535

T 1/2 (h) S (GY/GBq s) A terapia (GBq) Conteggi totali SPECT FEGATO MAX COUNT K (cGi) Max dose (cGi)

64,2 1,729 1,1 18031990 15410 3,518 54206

Radioembolizzazione mediante microsfere marcate con 90Y

- FEGATO SANO → 75% fase venosa (vena Porta) → 25% fase arteriosa (arteria epatica)

- TUMORE → 100% fase arteriosa

Radioembolizzazione con microsfere marcare 90Y • FASE DIAGNOSTICA - requisiti clinici - CT: valutazione lesioni - angiografia: studio morfologia arterie - 148MBq in 5ml di MAA marcati con 99mTc - WB e SPECT - Escludere shunt polmonare o gastro-intestinale

Radioembolizzazione con microsfere marcate 90Y

IPOTESI: - Biodistibuzione microsfere 90Y uguale a 99mTc-MAA - Nessun spostamento delle microsfere Prescrizione attività (da ditta produttrice): - 120 Gy al lobo da trattare

Gym

AD 12050=

⋅=

trichiesta eRLSFAA ⋅−⋅−⋅−

= λ)1()1(• FASE TERAPEUTICA - angiografia: eventuale embolizzazione shunt; iniezione microsfere - WB e SPECT (bremsstrahlung)

• FOLLOW-UP - risposta terapeutica: RECIST, WHO, EASL - tossicità: bilirubina, albumina, Child

SHUNT

Immagini CT, SPECT e fusione 99mTc MAA pre terapia 90Y post terapia

Dosimetry of microspheres

SASd tAD~

∫ ==

Microspheres are trapped in microcapillary.

No biological clearance. Only physical decay

Only one scintigram is enough !

The integral is very easy

D = A / λ * S = T1/2 / ln2 * A *S

D [Gy] = 50 A [GBq] / M [kg]

Dosimetry of microspheres: a lot of strong points

• No biological clearance: one SPECT is enough • Only one source-target organ • Homogeneus medium • Non penetrating radiation • Optimal gamcacamera imaging with 99mTc

Multiple time points: hard task • 3D approach • A real 3D dosimetry

should consider one TACT for each voxel

• This requires to exactly realign each SPECT

• Rigid or non rigid SPECT coregistration are necessary

• 2.5 D approach • TACT is averaged on

the whole lesion/organ

• TACT is derived from a sequence of planar, or from mean SPECT counts

• Dose distribution is 3D from one SPECT

INT METHODS

AND SIMULATION

RESULTS

Radiobiological parameters Non tumoral parenchima

α/β = 2.5 Gy

Trep = 2.5 h

Tumor tissue

α/β = 10 Gy

Trep = 1.5 h

Krishnan et al Am J Clin Onc (2006) 29:562-567

Tumor tissue

O’Donoghue

J Nucl Med 1999

α1 = 0.2 / Gy

α2 = 0.35 / Gy

α3 = 0.5 / Gy

Non tumoral parenchima

Jackson et al

Int J Rad Onc Biol Phys 31:883 (1995)

D1/2= 41.6 ± 3.5 Gy (non cirrhotic)

β=0 ½=exp(-α 41.6) α = 0.0166 Gy used

BED = 41.62 [ 1 + 1.5/2.5]

β≠0 ½=exp(-α BED) α = 0.0104 Gy ongoing

Other values for microspheres ? Surely yes

RADIOSENSITIVITY α

The absorbed dose in each voxel by voxel convolution

voxelphysvoxels ATA ⋅⋅=2

1443.1~

We choose Ãs from diagnostic SPECT with 99mTc-MAA, mainly for two reasons: - Goal: develop a previsional dosimetry tool - Poor image quality of 90Y bremstrahlung imaging - S voxel-voxel from www.df.unibo.it/medphys

)(:)()(:)( 90999099 YATcCountsYATcCounts totalm

totalvoxelm

voxel =

A patient relative calibration method was adopted

( )∑ ←⋅=voxel

voxelvoxelvoxels

stst SAD ~

Extensive code validation was performed 1. Virtual SPET to exclude statistical noise, compared with theoretical calculation

1. 1 source voxel, 2x2x2 source voxel 2. uniform cube sources 48x48x48, 60x60x60 3. Uniform cube with internal cube contrast 3:1 to test DVH

2. Real objects: cylinder uniform phantom compared with theoretical calculation

m

ETA

mEA

DdmdED

⋅

⋅⋅=

⋅=⇒=

2ln

~2

10 ββ

=

=⇒

hTkeVE

Y2,64

935

21

90 βTheoretical calculation

Warning: the theoretical calculation neglects

Border effects

bremstrahlung

CLINICAL RESULTS

Clinical background • 46 intermediate/advanced HCC treatments considered

• Glass spheres (Therasphere by MDS Nordion)

• Treatment planning: 120 Gy to lobe

• Toxicity G1 G2 G3 (liver failure 21% , ascites 19%): 40%

• Efficacy on lesions (CT density reduction > 50%): 46%

• Retrospective dosimetry on 99mTc MAA SPET images

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100

Dose (Gy)

Vol

ume

(%)

11 GBq

Dose Volume Histograms Healthy parenchima lesion

A jump to a smaller scale was done. From organ to organ, to voxel to voxel irradiation

The dose distribution is considered uniform at voxel scale.

This is still an approximation, but the closest to reality we can reach in vivo.

0 100 200 300 400 500 600 700 800 9000

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Dose (Gy)

Vol

ume

(%)

Toxicity: basal Child = A5 No correlation with any dose parameter

Child = A-5

No compl

Compl0

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40

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80

100

120

Mea

n vo

xel a

bsor

bed

dose

(Gy)

Child = A-5

No compl

Compl0

20

40

60

80

100

EUD

(Gy)

Child = A-5

No compl

Compl0

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200

300

400

500

Mea

n B

ED o

n vo

xels

(Gy)

Child A-5

No compl

Compl0

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100

150

200

EU_B

ED (G

y)

MTD 5/5 = 30 Gy

MTBED 5/5 = 54 Gy

Is the toxicity caused by the treatment ?

Child > A-5

No compl

Compl0

20

40

60

80

100

120

p = 0.22

Mea

n vo

xel a

bsor

bed

dose

(Gy)

Child > A-5

No compl

Compl0

20

40

60

80

p = 0.16

EUD

(Gy)

Child > A-5

No compl

Compl0

100

200

300

400

p = 0.22

Mea

n B

ED o

n vo

xels

Child > A-5

No compl

Compl0

20

40

60

80

p = 0.17

EU_B

ED (G

y)

Toxicity: basal Child > A5 Equivalent uniform parameter

MTD 5/5 = 30 Gy

MTBED 5/5 = 54 Gy

Tumors: good dose-response correlation according to EASL (tumor Hounsfield density)

( )bxaey ⋅−−= 191 lesions→21 with volume < 1cm3 excluded

Mean D vs EASL α = 0.2 / Gy

500 1000 1500

-0.5

0.0

0.5

1.0

R2=0.37Spearman r = 0.62p<0.0001

D (Gy)dens

ity r

educ

tion

EUD vs EASL α=0.2/Gy

200 400 600 800 1000

-0.5

0.0

0.5

1.0

R2=0.52Spearman r=0.71p<0.0001

EUD (Gy)

Mean BED vs EASL α = 0.2 / Gy

2000 4000 6000

-0.5

0.0

0.5

1.0

R2=0.34Spearman r=0.60p<0.0001

BED (Gy)

EU-BED vs EASL α = 0.2 /Gy

1000 2000 3000

-0.5

0.0

0.5

1.0

R2=0.52Spearman r = 0.71p<0.0001

EU-BED (Gy)

Dose-response correlation coefficients

Vol > 1 mL

Mean value

Equivalent uniform

valueMean value

Equivalent uniform

valueMean value

Equivalent uniform

valueD 0.37 0.52 0.37 0.52 0.37 0.52

BED 0.34 0.52 0.34 0.51 0.34 0.48D 0.06 0.17 0.06 0.17 0.06 0.18

BED 0.05 0.16 0.05 0.16 0.05 0.17D 0.12 0.28 0.12 0.29 0.12 0.30

BED 0.11 0.27 0.11 0.26 0.11 0.27

Alpha=0.35 / Gy Alpha=0.5 / Gy

WHO

RECIST

EASL

Alpha = 0.2 / Gy

1) EASL gives better correlations

2) Correlation is independent from alpha (good news !)

3) Correlation is always better using EU values, i.e. including non uniformity of dose distribution

Tumors: correlation dose-response according to EASL (tumor Hounsfield density)

Mann Withney test p<0.0001 PD+SD vs PR+CR Dose media VS EASL (α=0.2/Gy)

PD SD PR CR0

500

1000

1500

D [G

y]

EUD VS EASL (α=0.2/Gy)

PD SD PR CR0

500

1000

EUD

[Gy]

BED VS EASL (α=0.2/Gy)

PD SD PR CR0

2000

4000

6000

BED

[Gy]

EU-BED VS EASL (α=0.2Gy)

PD SD PR CR0

1000

2000

3000

EU-B

ED [G

y]

Dose as marker for EASL response ROC analysis

Strigari et al JNM 2010 • 90Y therapy images • Mean dose D

AUC = 0.59 [0.44 – 0-71]

Chiesa et al EANM 2010

• 99mTc diag. images • Mean dose D

AUC = 0.81 [0.70 – 0.91] • EUD

AUC = 0.88 [0.79- 0.96]

99mTc-MAA SPET dosimetry better separates responding – non responding lesion populations

Present treatment planning schema

• Prudence & courage

• Clinical conditions:

– Child,

– necessity of two lobe treatment

– irradiated fraction

• Any lesion (including only viable region) EUD > 200 Gy

• Whole liver “healthy” tissue (excluding tumors and necrotic part)

EU_BED < 54 Gy

WITH PRUDENCE

NOTA BENE: such dose limits should not be applied to resin spheres !

Voxel dosimetry leaded to different activity prescription !

-100%

-50%

0%

50%

100%

150%

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00-

Jan-

000-

Jan-

000-

Jan-

000-

Jan-

00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

(vox

el a

ctiv

ity -

prot

ocol

act

ivity

) pr

otoc

ol a

ctiv

ity

Comparison of injected activity according to protocol and voxel dosimetry & Child method

In 20 % of cases activity increase, in 40 % of cases activity decrease

SOFTWARE

AVAILABLE

VoxelDose

J Nucl Med 2010 51:1600

arnaud.dieudonne@bjn.aphp.fr

VoxelDose • Voxel convolution

based • Allows delineation of

tumor and parenchyma

• D mean, Dmin, Dmax, DVH

• Dieudonnè et al JNM in press

• Applied to liver treatment • Dmean in optimal

agreement with compartmental model

• Fast calculation: 1 h • 45 min needed for

manual segmentation • Allows to draw ROIs on

SPECT-CT coregistered images

• It is a too heavy machinery. Import – export from imageJ

• Dieudonnè itself: VoxelDose cannot be distributed yet

VoxelDose:

Comments from an user: Federica Fioroni Fioroni.federica@asmn.re.it

Reggio Emilia 0522 296653

PHILIPS: STRATOS Voxel dosimetry software running under Windows 7 NVIDIA graphic board advised Sequence of quantitative SPECT or PET needed (problem left to users !) 2.5 D modality available in 6 months (one SPECT and sequance of planar) Price: 50’000 euro (37’000 in a recent sale) Commercial bug under solution: no CE mark Software tool in strong evolution and development with easy company –

user communication

56

Integration into complete Planning Workflow

TRT core algorithms (e.g. voxelized S-value approach)

STRATOS: Dosimetry workflow

PET/SPECT-Quantification

Organ Segmentation

Dose calculation

Therapy plan

Image Data Import

Image Registration

TAC Fitting / Integration

Organ Segmentation

Dose calculation

Therapy plan

Image Data Import

Image Registration

TAC Fitting / Integration

TRT core algorithms (e.g. voxelized S-value approach)

Image registration • Many SPECT are coregistered to a single reference CT

– Advantage: no need to repeat CT scan

• Rigid and non rigid coregistration algorithm

• Non rigid not good according to Philips itself

• Manual coregistration available

Patient data courtesy: Prof. Kirsch / Dr. Hellwig, UK Homburg

Screenshot: Registration Workstep

PHILIPS: STRATOS • The DVK is radionuclide specific and depends on the Voxel

dimensions that are used in the grid. The DVK for certain radio nuclides is determined experimentally using Monte Carlo simulations and several codes, like ETRAN, EGS4 and Geant, to calculate the dose volume kernel have been developed [Giap 1995; Loudos 2009].

• DVK for different voxel sizes is provided by the company

• The convolution of the residence time map with the DVK yields a dose per activity map [Gy/Bq].

• When this is multiplied with the administered activity a dose map can be calculated which displays the dose per Voxel [Gy].

STRATOS: extrapolation to infinite time to be improved

Method 1: only the area under the curve

between the time of injection and the last scanning time point is calculated.

Method 2: linear extrapolation or physical decay

0,010

0,100

0 24 48 72

FIA

t-t0 (h)

177Lu DOTATATE Left KIDNEY

STRATOS: segmentation

• ROI have to be manually drawn

• For 3D region selection, one needs to navigate through the axial planes, adding contours every now and then (??).

• When one is finished with this, the system will interpolate the drawn contours, such that in every slice containing the selected region, the ROI is drawn.

• volume [ml], # of voxels, and min, max and mean Voxel intensity, of the ROI can be shown

STRATOS: calibration with cylindrical phantom

(absolute calibration) STRATOS uses a calibration factor (CF) to quantify the SPECT scans.

In order to find such a calibration factor, which is specific to each imaging system and depends on the acquisition settings, a phantom study is required.

For this one conducts a (NEMA) phantom experiment. It is best to have a Phantom that is anthropomorphic. The mean counts per ml in this region needed to be extracted in order

to be able to calculate the CF

63 Patient data courtesy: Prof. Kirsch / Dr. Hellwig, UK Homburg

Screenshot: Dose evaluation workstep

STRATOS: treatment planning Time activity curve Differential and integral histograms

65 Patient data courtesy: Prof. Kirsch / Dr. Hellwig, UK Homburg

Screenshot: Dose evaluation workstep

STRATOS: correction for non homogeneus media Now an experimental solution for Voxulus exists that translates a CT map into a density

map and corrects the absorbed dose with that density. In that sense, we are effectively just modifying the amplitude of our DVKs, not the shape

Dose in water-like material Dose corrected with density (not correct for tissue with other density than water)

• Partial volume effect: 4 mathod for correction

• Easy counturing tool

• It speeds up the whole calculation

• Comparison fully manual calculation with OLINDA vs STRATOS: quantitative agreement about mead D

STRATOS

Comments from an user: Federica Fioroni Fioroni.federica@asmn.re.it

Reggio Emilia 0522 296653

La voxel dosimetry pone nuovi problemi

JNM 2004

Dose alle lesioni (124I previsionale)

100 Gy (5-720) 270 Gy

(10-1700)

170 Gy (17-760)

350 Gy (37-1000)

100 Gy (6-880)

Dose assorbita prevista con somministrazione di for 15 GBq 131I

Courtesy of George Sgouros JNM 2004

Come interpretare la non uniformità di dose a livello di voxel ?