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4D: Adaptive Radiotherapy & Tomotherapy

Bhudatt Paliwal, PhD

ProfessorDepartments of Human Oncology & Medical Physics

University of WisconsinMadison

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Additional Contributors to this Talk

W. TomeDept of Human Oncology

T. McNutt, M. Kaus, V. Pekar, Philips Medical Systems

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Radiation Oncology Workflow

Simulation Immobilization

Forward PlanningTreatment setup

Dose computation

Inverse PlanningDefine Objectives

Optimize

Plan Analysis

Delivery System QA Dose Accuracy

Verify and Monitor Delivery

Deliver Treatment

Pre-Verify Dose/Position

Export to Delivery System

Target and Structure Definition

Image Patient

Adaptive Analysis

Pretreatment CT Guidance

Modify Plan/Patient Position

Multi-modality Imaging

Planning4D ComponentsDelivery

Export for Population

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Where is the greatest uncertainty now?

Treatment Uncertainties

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0.1

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-50 -40 -30 -20 -10 0 10 20 30 40 50Deviation from ideal

Pro

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bilit

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Target

Biology

Motion

Setup

Delivery

Dosimetry

Total

IMRT Improved Delivery Uncertainty

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4D Radiotherapy Adaptation Considerations

Radiobiology

Portal Images

On-line Imaging(Spirometry)

Fractionation

Setup Error

Organ Motion

Plan Modification

Target Re-Assessment

Tumor Response

PhysicianPatient

Dose Verification

4D Dose Eval

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4D Approaches - Frequency

• Multi-Fraction - Weeks– Monitor course of treatment and modify

plan at intervals of multiple treatment fractions

• Inter-Fraction - Day– “Plan of the Day” treatments– Prostate, Head and Neck

• Intra-Fraction - Seconds– Use 4D images to generate plans that

adapt to breathing cycle during treatment– Lung

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4D Breathing

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• Is it possible to daily re-plan?– 3D Conformal? IMRT?

• Is it practical to manage all the accumulated data offline and periodically re-plan?

• Are breathhold techniques acceptable or do we require dynamic motion compensation in our delivery?

• Is the incremental clinical benefit worth the cost?

• Can the process be made efficient enough for the busy clinic?

• Could we increase time per fraction and reduce the number of fractions to improve delivery?

– Biology?– Reimbursement?

4D Treatment Planning4D Treatment Planning

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4D Component Organization

4D Data Management• Time Series Volume Data• Record of Treatment Delivery• Time Series Portal Images

4D Image Processing• Deformable Registration• Model Based Segmentation• Organ Propagation• 4D Visualization

4D Evaluation• Organ Motion Analysis• Setup Error Assessment• 4D Dose Evaluation• Radiobiological Assessment

4D Treatment Planning• Geometric Uncertainty Planning • Adaptive Plan Modification• Automatic Re-planning (3D, IMRT)• Intra-fraction Motion Planning

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Align IsocenterAlign TxCT withContours

Determine translation (and rotations)

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Respiratory Gating

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PROSTATE EXAMPLE (Model-Based Image Segmentation*)

*Model-based image segmentation is a work in progress

Drag and Drop organs to Initialize Segmentation

Use 3D edit tool to improveinitialization for rectumPerform model-based

auto segmentationFine adjust with 3D edit tools

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Use 3D edit tools to improve breast modelsContinue adaptation to image dataSegmentation completeAdapt organ models to the image dataDrag and Drop OrgansUse 3D edit tool to initialize spine

BREAST EXAMPLE( Model-Based Image Segmentation*)

*Model-based image segmentation is a work in progress

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Summary

• 4D RT concepts represent a challenging new step for radiation oncology

• Various image processing tools show promise in automating the image segmentation process to identify organ motion

• Data management and automated analysis are required to enable adequate monitoring of the course of treatment

• Molecular imaging may play a strong role in assessing tumor response to therapy

• Economical benefit may be realized in the trade-off be geometrical vs. radiobiological sparing of normal tissues with reduced the number of fractions, and daily re-planning