4D Target Definition: How to deal with a moving target Dr Thirion Lung Stereotactic National Lead Clinician

Overview • Respiratory related Tumour Motion: Background – Main challenge in Pulmonary SABR – Not predictable / individualised / temporal variation

• Respiratory-related Tumour Motion: Impact on Radiotherapy – GTV delineation – Planning impact: Interplay effect

• Methods to account for respiratory motion in radiotherapy – Free breathing methods: Motion encompassing vs. Respiratory gated methods – Breath-hold techniques – Real-time tumour tracking methods 3rd Annual SRS/SBRT Annual Symposium 2

Breathing Mechanics

• Breathing pattern variations - Position ( upright / prone / supine / lateral decubitus) - Depth of respiration - Breathing type (chest / abdominal)

3rd Annual SRS/SBRT Symposium

Tumour Motion: Inter-patient variation

Key findings: Tumour motion - From 1 mm to > 2cm, < 1 cm in 78% of patients - Non-linear in 50% 3rd Annual SRS/SBRT Symposium

Tumour Motion: Intra-patient variation

3rd Annual SRS/SBRT Symposium

3D Ct scan : Limitations

• Standard non-4D radiotherapy Ct scan limitations: – Fast acquisition Helicoidal Ct Scan = snapshot – No appreciate the full tumour motion – Risk of motion related distortion affecting tumour shape and size

•

3rd Annual SRS/SBRT Symposium

3D Ct scan : Limitations

Multiple snapshots

One snapshots

3rd Annual SRS/SBRT Symposium

3D Ct scan : Limitations

• Tumour motion and speed of CT scan acquisition • If CT scanning speed acquisition > tumour motion speed – Tumour position & shape captured at an arbitrary

• breathing phase (= systematic error) • If CT scan speed = tumour motion speed – Tumour position & shape distorted

3rd Annual SRS/SBRT Symposium

3D Ct scan : Limitations

3rd Annual SRS/SBRT Annual Symposium

4D CT: New Gold Standard ?

• Advantages: – Reduce motion artefact – Provide Tumour / organ motion information

• Limitations: – Temporal information limited to one breathing cycle – Irregular breathing pattern will still cause artefacts – Minimal breath coaching always required

3rd Annual SRS/SBRT Annual Symposium

Planning and delivery limitations- interplay effect

Motion of the tumor and of the MLC leaves – can create unexpected hot/cold spots, especially in the areas of high gradients

Patient No

RM

PTV

Amplitude (cm) V100

PTV min CTV V100 dose

CTV min dose

1

1.6

-15.4%

-43%

0%

0%

2

1.0

-6.5%

-15%

0%

2%

3

1.0

-8.7%

-14%

0%

-2%

4

0.8

-5.8%

-12%

0.3%

2%

5

0.8

-5.4%

-10%

0%

0%

6

0.5

-0.7%

-3%

0.7%

3%

Interplay effect

3rd Annual SRS/SBRT Symposium

Methods to account for respiratory motion in radiotherapy

• Free breathing methods – ITV based method (= Motion encompassing methods) – Mid-Ventilation based method (= Motion encompassing methods) – Gating (Respiratory gated methods)

• Breath-hold technique – Deep Breath Hold Method – Active Breathing Control (ABC) – Self-Held Breath Hold with respiratory monitoring

• Real-time tumour tracking methods

3rd Annual SRS/SBRT Symposium

3rd Annual SRS/SBRT Symposium

Free Breathing Methods

3rd Annual SRS/SBRT Symposium

ITV based Radiotherapy • Definition – ITV = composite GTV , including all phases

• Delineation technique (Listen to Alina) – MIP not enough ! – All phases should be checked

• Advantage: – Can be used with all delivery technique (3D / IMRT / Tomotherapy)

• Disadvantage: – Large Volume – Predictability of respiratory motion – Interplay effect, if IMRT 3rd Annual SRS/SBRT Symposium

Mid-Ventilation based Radiotherapy

Principles: • Treat tumour in average position • Benefit of wide-beam penumbra in the lung • Under-coverage of GTV for a small part of breathing cycle • Estimated 0.6% and 6% TCP loss if 5 and 15 mm amplitude if PTV = GTV

3rd Annual SRS/SBRT Symposium

Tumour Motion: Intra-patient variation

3rd Annual SRS/SBRT Symposium

Respiratory Gated Methods

3rd Annual SRS/SBRT Annual Symposium

Respiratory Gated Methods

• Treatment delivery limited to selected breathing phases • 2 types of Gating: • Internal gating – fluoroscopy – Principe : tumour visualisation / fiducials / internal organ as surrogate – Products: RTRT system , Exatract

• External gating – optical gating – Principles ; external respiratory surrogates , eg abdominal surface – Product: Varian RPM, Visio RT, Anzia Belt,

3rd Annual SRS/SBRT Symposium

Respiratory Gated Methods

• Requirements – 4D treatment delivery ability

• Tumour Motion (surrogate or direct ) – Predictability of tumour motion – No interplay effect

3rd Annual SRS/SBRT Symposium

Varian RPM system

3rd Annual SRS/SBRT Symposium

Respiratory External Gated Methods: Limitations (1)

Tumor Home Position and Instant Position

3rd Annual SRS/SBRT Symposium

Respiratory External Gated Methods: Limitations (2) • During treatment simulation, the reference home position should be accurately measured, using techniques such as 4D CT. • During treatment planning, the patient and tumour geometry at the reference home position should be used. • During patient setup, the tumour daily home position should be matched to the reference home position. • During the treatment delivery, the tumour home position should be maintained the same

3rd Annual SRS/SBRT Annual Symposium

Respiratory External Gated Methods: Limitations (3)

• Limitations - Correlation between tumour position / motion and external marker position / motion may vary, leading intra or/and inter fractionation variation - QA recommended (Fluoroscopy)

3rd Annual SRS/SBRT Symposium

Respiratory Internal Gated Methods

Hokaido system • Real-time fiducial tracking by 2 IR camera, with 3D reconstruction • Comparison to pre-treatment reference images allowing to define gating window • High exposure (fluoro monitoring ) / markers insertions 3rd Annual SRS/SBRT Annual Symposium

Internal Gating

Extract / Novalis Body System • Combination of optical surface and fluoroscopybased internal tracking system, allowing 1. Check of pt position (surface fiducial ) coupled with table correction 2. Stereoscopic camera checking internal fiducial / organ position

3rd Annual SRS/SBRT Symposium

Breath-hold techniques

3rd Annual SRS/SBRT Annual Symposium

Breath-hold techniques ABC / DBH • Advantages – Minimal PTV volume – No tumour motion – No interplay effect

• Disadvantages – Patient suitability – Treatment interruptions – Residual “motion”, intra breath hold variation

3rd Annual SRS/SBRT Symposium

Real-time tumour tracking methods

3rd Annual SRS/SBRT Annual Symposium

Real-time tumour tracking methods • Synchrony system • Advantages – Real tracking – Small volume – No treatment interruption

• Limitation – Fiducial – 2 D tumour visualisation – OAR ??

3rd Annual SRS/SBRT Symposium

Thank You

3rd Annual SRS/SBRT Symposium