4D Stereotactic Lung IMRT Planning 4D Stereotactic Lung IMRT Planning using Monte-Carlo Dose Calculations using Monte-Carlo Dose Calculations on Multiple RCCT-based Deformable on Multiple RCCT-based Deformable

GeometriesGeometries

Matthias Söhn1, Di Yan2 and Markus Alber1

(1)University of Tübingen, Radiooncological Clinic, Sect. f. Biomedical Physics, Tübingen, Germany

(2)William Beaumont Hospital, Radiation Oncology,Royal Oak, MI, USA

Forschungszentrum für Hochpräzisionsbetrahlung

2 UKTübingen

SRT for small lesions with large mobility:SRT for small lesions with large mobility:Problems of margin-based, static planningProblems of margin-based, static planning

ITV

PTV

large margins necessary!

dose to large normal tissue volume

restricts tumor dose

what geometry is to be used for dose calculation?

3 UKTübingen

SRT for small lesions with large mobility:SRT for small lesions with large mobility:Problems of margin-based, static planningProblems of margin-based, static planning

static dose distribution,calculated on average CT

…large CTV-motion relative to static planning geometry

…dose distribution changes with CTV-motion

…the actual “dynamic” dose distribution!

static planning

exhaleposition

inhalepositiontumor spends more time in upper part of PTV

region (exhale) than in lower part (inhale)

Is it actually necessary to cover whole PTV region with full dose?

optimize actual dose-to-moving-CTVgated treatment

“Tissue-eye-view”

4 UKTübingen

4D IMRT Planning…4D IMRT Planning…

Our approach in the following:

optimization of the expected dose in moving tissue (Tissue Eye View)

5 UKTübingen

The road to Tissue-Eye-View:The road to Tissue-Eye-View:Dose warping to a reference phaseDose warping to a reference phase

beamlet dose…calc. in different geometries

6 UKTübingen

The road to Tissue-Eye-View:The road to Tissue-Eye-View:Dose warping to a reference phase Dose warping to a reference phase

warped to reference geometry

deformableregistration

beamlet dose…calc. in different geometries

7 UKTübingen

The road to Tissue-Eye-View:The road to Tissue-Eye-View:Probability density function (pdf) of breathingProbability density function (pdf) of breathing

0In

25In

50In

75In

100E

x75

Ex50

Ex25

Ex0

0.1

0.2

0.3

0.4

0.5

time [s]0 50 100

ampl

itude

[a.

u.]

relative time spend in CT-bin=> relative weights

pdf

time [s]

am

plit

ud

e

0

100

statistical description of breathing motion!

8 UKTübingen

Tissue-Eye-View: expected dose-to-moving-tissueTissue-Eye-View: expected dose-to-moving-tissue

beamlet dose…calc. in different geometries warped to reference geometry

accumulated inreference geometryusing breathing PDF

TISSUE EYE VIEW

accumulated expected dose distribution in moving tissue, shown in reference geometry

optimizatio

n in tis

sue-eye-view!

optimizatio

n in tis

sue-eye-view!

9 UKTübingen

4D- vs. margin-based static planning: A test case4D- vs. margin-based static planning: A test case

Idealized assumption: perfect daily target-based setup, i.e. no setup-margin

free-breathing PTV-plan: PTV = ITV of all 8 RCCT-phases

free-breathing 4D-plan: optimization of expected dose in ‘tissue-eye-view’ with explicit dose calculation in all 8 RCCT-phases

exhale-gating PTV-plan: PTV = ITV of 3 RCCT-phases around exhale

Comparison of 3 plans…

Implemented using IMRT-software Hyperion:

EUD-based, constrained optimization

Monte-Carlo dose calculation (XVMC)

Prescription: 55Gy EUD to target in 11fx constraints to target (limited overdosage), lung and other unspecified tissue

11 beams

10 UKTübingen

Results: Dose distributions (coronal view)Results: Dose distributions (coronal view)

static dose

accumulated dose accumulated dose

static dose

accumulated dose

57.8Gy 52.2Gy 46.8Gy 38.5Gy 22.0Gy 16.5Gy 11.0Gy27.5Gy

free-breathing PTV-plan exhale-gating PTV-plan free-breathing 4D-plan

lung sparing

11 UKTübingen

Results: Target DVHs (accumulated CTV doses)Results: Target DVHs (accumulated CTV doses)

gating and 4D-plan with similar doses

to moving CTV

free-breathing PTV-plan: lowest and most

inhomogeneous CTV-dose

12 UKTübingen

Results: DVHs of OARs (accumulated doses)Results: DVHs of OARs (accumulated doses)

left (contralateral) lung

skin/unspecified

right (ipsilateral) lung

constraints met similarly well for all plans

13 UKTübingen

Results: EUDs & dosimetric parametersResults: EUDs & dosimetric parameters

objective constraints

EUD

[Gy]

rms overdosage

[Gy]

prescription 55.0 2.0

PTV-plan

-static dose

-accumulated dose

45.1

47.4

1.93.2

gating plan

-static dose

-accumulated dose

49.3

50.9

1.9

2.3

4D-plan

-accumulated dose 50.2 2.0

14 UKTübingen

Results: EUDs & dosimetric parameters, performanceResults: EUDs & dosimetric parameters, performance

objective constraints

calculation time

segmented, fully optimized plan

(Monte Carlo)

EUD

[Gy]

rms overdosage

[Gy]

prescription 55.0 2.0

PTV-plan

-static dose

-accumulated dose

45.1

47.4

1.93.2

60mingating plan

-static dose

-accumulated dose

49.3

50.9

1.9

2.3

4D-plan

-accumulated dose 50.2 2.082min voxel-size: 3mm; beamlet-size: 4x2mm

stat. accuracy MC dose calculation: 3% (3.5•106 histories/segment) dual-quadcore Intel Xeon @ 2.66GHz (8 CPU cores), 16GB memory

15 UKTübingen

Summary & ConclusionsSummary & Conclusions

4D-planning:optimization in Tissue-Eye-View!

explicit dose calculation in multiple geometries using Monte Carlo deformable registration, allowing dose warping to reference geometry optimization of expected dose: dose accumulation in reference geometry using Probability Density Function (pdf) of breathing

potential of dose escalation compared to free-breathing PTV-based planning equal target coverage as gated-treatment, but reduced workload during treatment

16 UKTübingen

Appendix: Fluence Appendix: Fluence distributionsdistributions

PTV plan 4D plan

155

deg

ree

-65

de

gre

e-1

25 d

egre

e