Motion gating and tracking techniques: overview and recent...

Motion gating and tracking techniques: overview and recent developments

Gig S Mageras, PhD, FAAPM

Department of Medical Physics

Memorial Sloan Kettering Cancer Center, New York

MSK/gsm 15-Jun-2018 1

Disclosure

• Research support from Varian Medical Systems


Respiratory gating – some basics

• Intermittent delivery of radiation occurring within a portion of breathing cycle (gate)

• Gate onset/duration determined by respiratory monitoring, either external signal, imaging of internal markers, or electromagnetic tracking

• Usually gate set around end expiration: ↓ tumor motion

• In some apps (e.g. left breast), gate set at enhanced inspiration with coached deep breathing: ↑ normal tissue sparing


Gating – external monitors



Expiration Inspiration

Ohara et al. IJROBP 1989; 17:853

Triggered exposure on simulator

Irradiation synchronized with respiration gate – Univ. Tsukuba, Japan

Equipment/signal processing



Minohara et al. IJROBP 2000; 47:1097

Respiratory gated irradiation system for heavy-ion radiotherapy, Chiba, Japan



Kubo et al. Med Phys 2000; 27:346

Breath signal synchronized with fluoroscopy

Expiration Inspiration

Video camera-based breathing signal

Breathing-synchronized RT program at Univ. California, Davis



Varian Real-time Position Management (RPM)

Gating threshold levels

(amplitude based)

Beam enable intervals

Reflective marker block

Infrared video camera



Prospective RPM-triggered CT acquisition

• Acquisition in axial mode

• (1 slice with couch stationary, couch index to next position)

• RPM triggers issued to contrast injector port

• Each gate triggers 1 slice

• 100 slices takes ~ 9min

Philips PQ5000 single slice CT


mskcc/gsm 10Inspiration

Expiration #1

Expiration #2

Free Breathing

Comparison standard vs respiration-triggered CT - NSCLC


• Voice + visual instruction achieves consistent RPM marker motion

• Observed diaphragm deviations from plan:

• NSCLC, n=21: Systematic -0.1±0.6 cm, random 0.4±0.1 cm (similar in liver)

• Daily IGRT a necessity

RPM-gated RT exhibits interfractional external-internal variation

Yorke et al, JACMP 2003; 6:19


Inconsistent gating accuracy may occur within 1 RT session even with daily IGRT


Ge et al, IJROBP 2013; 85:854

• Studied implanted fiducials in abdomen, RPM amplitude-gated, n=12• ↓ accuracy in 44% of daily fluoro movies• Recommend > 2.5mm safety margin



Pedersen et al. Radiother Oncol 2004; 72:53

Breathing adapted RT of breast cancer: reduction of cardiac and pulmonary doses using voluntary inspiration breath-hold


Gating – internal fiducials



Mitsubishi/Hokkaido Real-Time Tumor-Tracking (RTRT) system

Detected marker

Planned position

Allowed displacement

Image

intensifiers

X-ray

tubes

Gating – internal fiducials

(3)Shirato et al, IJROBP 2000; 48:1187

Prospective Cohort Study of Gated SBRT Using Continuous Internal Electromagnetic Motion Monitoring


Worm et al. IJROBP 2018; 101:366

Calypso monitor screen

Gating – electromagnetic tracking

Patient example at one session



Gray: CBCT scan. Green: beam-on. Red: couch adjustments

Motion in sagittal plane during CBCT (black) and last field of nongated RT (red)

Mean drift: 8mm sup, 5mm post

Gated

Not gated




Gated vs simulated Not gated, n=15, 3 fx


Calypso-gated RT in lung @MSK (protocol)



Axial

Coronal

4DCT at expiration

Calypso-gated RT in lung

Orthogonal kV pair with tracking templates overlaid (blue)



Formation of respiratory motion-corrected CBCT

Dzyubak et al. Med Phys 2014; 41:101918


Track beacons in projection images

CBCT scan

Amplitude sort into 10 bins, reconstruct

each bin

Deform each reconstructed bin to expiration state (model from 4DCT)

Sum

Motion-corrected CBCT


Axial

Coronal

Plan CT (FB) CBCT 4DCT end-expiration CBCTTrueBeam Motion corrected


Verify beacon positions in lung relative to tumor, with motion-corrected CBCT

Calypso beacon



Calypso-gated RT in lung Couch adjustment

Beam on (gated)

Gated CBCT uses a script to gate gantry rotation & kV image acquisition

Kincaid et al, Med Phys 2013; 40:041717

Video courtesy Michelle Svatos

26MSK/gsm 15-Jun-2018

Developer Mode, Varian TrueBeam

Gated CBCT improves tumor visibility in lung, …



Standard CBCT Gated CBCT

…and soft tissue visibility in pancreas.

Standard CBCT Gated CBCT



Motion tracking


Some basics

• Continuous adjustment of radiation beam or patient position to follow the changing position of the target or its surrogate

• A means of localizing the target in real-time is coupled to a target alignment control system

• Instructions to alignment control includes correction for system latency (motion prediction)


Dieterich et al. Med Phys 2008; 35:5684

Motion tracking


Ozhazoglu et al. Med Dosim 2008; 33:117

Motion tracking

Accuracy of Cyberknife lung tumor tracking: analysis of log files

• Correlates external optical signal with kV imaging of internal fiducials every 30-60 s

• Correlation may fail with irregular breathing, baseline drift, or large target rotation

• Analysis of treatment log files, early-stage NSCLC or isolated lung met, n=44:


Motion amplitude (mm)

SD

in

tra-f

xe

rro

r (m

m)

Motion amplitude (mm)SD

pre

dic

tion

err

or

(mm

)

Hoogeman et al. IJROBP 2009; 74:297

Motion tracking


Keall et al. Radiother Oncol 2018; 127:6

KIM 2D-to-3D transformation assumes correlation of motion between observed & unobserved directions. Unobserved motion based on prior observations.

Real-time image-guided adaptive RT in prostate using a standard linac

Motion tracking


Keall et al. Radiother Oncol 2018; 127:6

Motion tracking – worst-motion case with drift in all 3 directions

MV/kV Intratreatment Imaging for Prostate SBRT



Plan hot spot increases 0.5-1.0%

Slide courtesy Perry Zhang

Modification of MLC control-point (CP) sequence to increase fiducial visibility

Copy of TxCP2

Copy of TxCP2

Zhang et al. Med. Phys. 2016; 43:2024

Simultaneous MV-kV intra-fractional motion management VMAT in prostate

MV/kV clinical process – patient setup

Before

After

Position-of-the-day 3D correction – kV/kV setup pair


Hunt et al. J Appl Clin Med Phys 2016;17:473

kV trigger during VMAT 3° MV-DTS

• Triggered kV + MV short-arc digital tomosynthesis @ 20⁰ intervals• Audio/visual alert if 2 mm tolerance is exceeded• Manual interruption and correction of position if needed


MV/kV clinical process – treatment Hunt et al. J Appl Clin Med Phys 2016;17:473


Booth et al. Radiother Oncol 2016; 121:19

First treatment of electromagnetic-guided real-time adaptive RT using MLC tracking for lung SABR


(VIDEO)

Booth et al. Radiother Oncol 2016; 121:19

MR-guided tracking and beam gating



3D MRI acquisitionExpiration breath hold

Select sagittal plane to track relevant

anatomical feature (target contour)

Assign boundary:Expand target contour or

any encompassing contour (e.g. PTV)

Cine:preview acquisition prior to start of delivery (40 s)

Evaluate: does target contour deform

accurately with observed anatomy for tracking?

Select ROI:Based on observed tracking, what % of

target is allowed outside boundary?

Start radiation delivery with continuous imaging

at 4 Hz

Gate off/on when anatomy of interest

outside/inside boundary

Green et al. Med Phys 2018 (accepted)

Implementation of real-time, real anatomy tracking and radiation beam gating

Workflow:

MR acquisition, anatomy tracking and beam gating


Green et al. Med Phys 2018 (accepted)

Commercial Systems, current and near future

• Gated linac +

– External monitor: Varian + RPM, Elekta + Catalyst

– X-ray imaging implanted markers: Mitsubishi/Hokkaido RTRT

– Electromagnetic tracking: Varian + Calypso

– MR-guided: ViewRay MRIdian, Elekta Unity (future: add gating)

• Motion tracking

– Robotic beam : Cyberknife Synchrony

– Couch tracking: experimental

– MLC: customized systems


Motion gating and tracking techniques: overview and recent...

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