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Accuray Radixact at University of WI: The next chapter in TomoTherapy

innovation

Jennifer Smilowitz, Ph.D.Clinical Associate Professor

Departments of Human Oncology and Medical PhysicsUniversity of Wisconsin, Madison, WI, USA

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Disclosure

This work is funded in part by the University of Wisconsin / Accuray research agreement.

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History of TomoTherapy at UW

1988: Tomo idea conceived by Rock Mackie at UW.

1997: TomoTherapy Inc. founded by Mackie and Reckwerdt

2002: First patient treated at UW. 2013/14: 2 HDA units replace the Hi-Arts 2015: Radixact research unit installed

Ken Ruchala

Dave Pearson

Jeni Smilowitz

John Balog

Rock Mackie

At UW Bench top unit, ~1999

First gantry ~ 2001

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IMRT/IGRT Integration into Clinical Practice

Del

iver

y Fe

asib

ility

SophisticationInitially a specialty machine: a pioneer for IMRT and IGRT

Improvements:• TomoDirect• Dynamic Jaw• DCS• VoLo• GPU processing• TQA • Easier plan

transfer• OIS connectivity• Fixed target

Hi-Art 20132005

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Current and Future Radixact Features

1. Key new hardware features– Higher dose rate (nominal 1000

cGy/min) – Additional magnetic shielding

around linac– Couch catcher

2. Gantry redesign with space for kV imaging system

3. Motion compensation4. Key software features :

– Precision iTPS– Common database– Integration with third party TPS

(RayStation)

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Project 1: Dosimetric Stability and Reliability

• Same linac and target as the latest HDA systems operating at higher dose rate.

• Energy and output of Radixact assessed as part of a larger investigation into the tomotherapy systems at UW.

• Smilowitz, JB, Dunkerly, D, Yadav, P, Hill, P and Geurts, M., Long Term Dosimetric Stability of Multiple TomoTherapy Delivery Systems, J Appl Clin Med Phys, Accepted March 2017

99.75 99.8 99.85 99.9 99.95 100 100.05 100Relative Output

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0.05

0.1

0.15

0.2

0.25

0.3

0.35

Fre

quen

cy

SN 477 HDA

SN 488 HDA

SN 05 Radiexact

Non-DCS systems DCS systems

Monitor Chamber, Relative Output

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Major Dosimetric Component Replacement History

The service record history does not cover the compete duration of the output and energy study due to limited availability of records for the Hi-Art systems.)

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….to a robust and sophisticated treatment ready for new features

Del

iver

y Fe

asib

ility

Sophistication

Hi-Art

• Space for onboard KV imaging• New couch features

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Project 2: Motion Compensation

• Accuray has proposed a method to compensate for intrafraction motion

• Helical, dynamic jaw plans created for 11 patient datasets (per IRB approval)

– ITV based plan (3 mm expansion of ITV) = PTV

– 3 mm expansion of GTV = PTV

• Dose distributions with motion generated to address:

– The effect of motion on intended plan created with an ITV

– The effect of motion mitigation

– The impact of smaller PTVs based on GTV expansion only

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Dose computation with Motion Trace

1. Motion trace was generated for the 11 cases (4 liver, 4 lung, 3 pancreas)

2. Contour GTV on single phase CT scan and use sequential deformable to propagate to all phases.

3. Identify center of mass (COM) 4. Combine COM motion

with RPM file(extend for tx. length)

Dose computed using a GPU-based tomotherapy dose code that rigidlytransformed dose according to trace.

Avg/min/max COM motion (cm): Lat. 0.8/0.1/1.4A/P 1.2/0.2/2.8S/I 1.9/0.8/3.5

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Fractional dose difference maps (note scale)

(a) Effect of intrafraction motion (Dose 2-1)

(b) Motion compensation (Dose 3-1)

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Results

* DC offset in motion trace

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Conclusion and next steps

• Tumor motion during TomoTherapy helical delivery produced plans with large volumes of tissue having substantial dose difference from planned dose.

• These differences were mitigated within clinically acceptable tolerances using MLC and jaw motion compensation, enabling further gain through margin reduction.

• Next steps:– Where are the regions of under and overdose?– Quantify effect of target coverage versus sensitive

structures

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Pancreas - example of effect of DVH

ITV based planWith motionMotion Compensated

Duod./stomach

liverGall bladder

kidneys

DVH has more information, but still tells an incomplete story…

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Project 3: Treatment Planning

• New integrated Data Management System( iDMS) with a new TPS based on CyberKnife interface, “Precision”

• Same GPU “VoLo” optimization• We are investigating the effect on planning with higher dose

rate by (manually) generating “dosimetrically equivalent plans” and looking at gantry period, treatment and leaf open histograms.

• We will soon begin testing a new transfer software (HDA to Precision Planning, then a machine transfer to Radixact)

• TomoTherapy planning RayStation (Phase 2 of our clinical TPS upgrade)

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How does the high dose rate effect planning?

Similar tomo “feel”

New features (ex: DxVv)

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“Dosimetrically equivalent” Plan Study

• Re-planned clinical cases to create “Dosimetrically equivalent” plans (within 1 Gy and meeting MD dose objectives)

– Maintaining planning parameters (MF, FW, pitch & objectives)

– Evaluation of DVH metrics and normal tissue objectives

• Look at resultant treatment times, not goodness of plan

D98

D2

D95

D50

PTV 70

PTV 56

PTV 60

Esophagus

Parotid_L

RadixactHDA

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Preliminary results to date: Treatment time

850 cGy/min

1000 cGy/min

“Dosimetrically Equivalent” plans

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850 cGy/min

1000 cGy/min

“Dosimetrically Equivalent” plans

Preliminary results to date: Gantry Period

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What happens to the Leaf Open Times (LOT)

with fast GP?

IliacSupraglottic HN

Rad

iexa

ctTo

mo

HD

A

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MVCT Scanning is ~ 40%Faster

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60

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Iliac Prostate Meningioma Head and Neck

Seconds

HDA RADIXACT

59.9 %

From Accuray study on UW Madison HDA clinical system and Alpha Radixact bunker (Cristina Negrut, Jeremy Heil and Jeff Sudmeier)

10 sec 6 sec

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Summary

• Alpha research unit for next generation TomoTherapy delivery system is installed in WIMR

• Initial testing shows Radixact is as stable and reliable as current clinical HDA systems

• Dose difference due to intrafraction motion is observed even with ITV-based plans. A rigid proposed motion compensation method is able to decrease dose differences.

• Higher dose rate reduces plan time as expected as gantry period speeds up. This also changes the the LOT histogram and will potentially allow for more delivery options, with less short LOT.

• Tomo research is exciting and ongoing here at UW.

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Thank you to many contributors on the various projects!

• UW Faculty– John Bayouth, Mark Geurts, Poonam

Yadav, Patrick Hill, Rock Mackie• Accuray Team

– Cristina Negrut, Andrea Cox, Calvin Mauer

– Ed Chao, Eric Schnarr, Jake Shea– Nancy Sauer and Rick Vaden

• UW Graduate Students– Erin Adamson– Mariajose Bedoya– Sarah Bitant– Vimal Desai– David Dunkerley– Sabrina Hoffman– Ian Marsh– Andrew Santoso– Catherine Steffel– Natalie Viscariello