1 volumetric modulated arc therapy - clinical implementation outline

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2010 ACMP Annual Meeting, San Antonio2010 ACMP Annual Meeting, San Antonio

Volumetric Modulated Arc TherapyVolumetric Modulated Arc Therapy--

Clinical Implementation Clinical Implementation

Daliang Cao, PhD, DABR

Swedish Cancer Institute, Seattle, WA


AcknowledgementAcknowledgement

David M. Shepard, Ph.D.David M. Shepard, Ph.D.

Muhammad K. N. Afghan, Ph.D.Muhammad K. N. Afghan, Ph.D.

Fan Chen, Ph.D.Fan Chen, Ph.D.

Min Rao, Ph.D.Min Rao, Ph.D.

Jinsong Ye, M.S.Jinsong Ye, M.S.

Tony P. Wong, Ph.D.Tony P. Wong, Ph.D.

Vivek Mehta, M.D.Vivek Mehta, M.D.

David HousleyDavid Housley

Igor Gomola, Ph.D.Igor Gomola, Ph.D.

Gerry Gerry VantellingenVantellingen

Jie Shi, Ph.D.Jie Shi, Ph.D.

Kris LyleKris Lyle


OutlineOutline

Basics of VMAT and its recent developmentBasics of VMAT and its recent development

VMAT treatment planningVMAT treatment planning

VMAT commissioning and QAVMAT commissioning and QA


History of VMAT History of VMAT

�� VMAT, formally known as Intensity Modulated Arc The rapy (IMAT), VMAT, formally known as Intensity Modulated Arc The rapy (IMAT), was first was first brought up by Dr. Cedric Yu in 1995.brought up by Dr. Cedric Yu in 1995.


IMATIMAT

�� 19951995-- Initial paper described the delivery technique and Initial paper described the delivery technique and demonstrated feasibility.demonstrated feasibility.


Basics of IMATBasics of IMAT

IMAT is a rotational IMRT that can delivered using IMAT is a rotational IMRT that can delivered using conventional linear accelerators with conventional MLC.conventional linear accelerators with conventional MLC.

Radiation is on while gantry is rotating with MLC l eaves Radiation is on while gantry is rotating with MLC l eaves moving continuously.moving continuously.

Intensity modulation is created by overlapping arcs .Intensity modulation is created by overlapping arcs .

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ARC 1

ARC 2

ARC 3

From Cedric Yu

IMAT DeliveryIMAT Delivery


Benefit of Rotational IMRTBenefit of Rotational IMRT

254425440.1550.1550.9330.9330.0380.0380.1510.1513333

254525450.1710.1710.9120.9120.0490.0490.1760.1762121

254225420.1800.1800.9080.9080.0530.0530.1870.1871515

257025700.1860.1860.8790.8790.0580.0580.2020.2021111

259925990.1920.1920.8550.8550.0640.0640.2220.22299

259725970.2060.2060.8670.8670.0640.0640.2420.24277

256425640.2150.2150.8140.8140.0900.0900.3180.31855

273327330.4880.4880.7470.7470.1240.1240.6650.66533

Total Integral Total Integral DoseDose

Mean Dose To Mean Dose To the Region At the Region At

RiskRisk

Minimum Dose Minimum Dose Covering 90% Covering 90% of the Target of the Target

(1.0 = Max)(1.0 = Max)

Standard Standard Deviation In Deviation In The Target The Target

DoseDose

Objective Objective Function ValueFunction Value

Number of Number of Beam Beam

DirectionsDirections

Improvement found by increasing the number of beam angles

Independent of the number of beam angles

D.M. Shepard, et al, Medical Physics, 26 pp. 1212 (1999); T.R. Mackie, et al, Intensity Modulated Radiation Therapy – The State of the Art, pp. 247 (2003)


IMAT: 1995IMAT: 1995 --20072007

Over this time, the IMAT delivery technique largely Over this time, the IMAT delivery technique largely withered on the vine.withered on the vine.

LinacLinac manufacturers did not have control systems manufacturers did not have control systems capable of delivering IMAT.capable of delivering IMAT.

No treatment planning system offered a robust No treatment planning system offered a robust inverse planning tools for IMAT.inverse planning tools for IMAT.


IMAT: 2008-2010

Elekta and Varian introduced control systems Elekta and Varian introduced control systems that are capable of delivering IMAT.that are capable of delivering IMAT.

Key innovation is that the dose rate, gantry Key innovation is that the dose rate, gantry speed, and MLC leaf positions can be changed speed, and MLC leaf positions can be changed dynamically during rotational beam delivery.dynamically during rotational beam delivery.

The term VMAT has been adopted.The term VMAT has been adopted.

The first robust commercial VMAT planning The first robust commercial VMAT planning solutions were introduced.solutions were introduced.

2010 ACMP Annual Meeting, San Antonio2010 ACMP Annual Meeting, San AntonioCourtesy of Varian Medical


Varian – The Single Arc Approach

VarianVarian’’s initial RapidArc solution focused s initial RapidArc solution focused exclusively on single arc treatments.exclusively on single arc treatments.

““RapidArcRapidArc”” requires a Varian requires a Varian linaclinac, OBI, EPID, , OBI, EPID, and Eclipse treatment planning.and Eclipse treatment planning.

Single arc delivery times are typically 2 minutes Single arc delivery times are typically 2 minutes or less.or less.

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Elekta VMAT – Key Features

One can simultaneously vary: gantry position, One can simultaneously vary: gantry position, gantry speed, leaves of the multigantry speed, leaves of the multi --leaf collimator leaf collimator (MLC), back(MLC), back--up diaphragm, and dose rateup diaphragm, and dose rate

Single Single oror multiple arc delivery multiple arc delivery

Coplanar or nonCoplanar or non--coplanar deliverycoplanar delivery

Collimator rotationCollimator rotation


Siemens – Cone Beam Therapy (CBT)

Siemens has a VMAT delivery solution under development.

Their approach is based on delivering bursts of radiation symmetrically about a series of discrete beam angles during gantry rotation.

The beam is turned on and off during the gantry rotation with dose rates up to 32 MU/sec.


VMAT Treatment PlanningVMAT Treatment Planning


Commercial Planning SystemsCommercial Planning Systems

Elekta Ergo++Elekta Ergo++®®

Elekta MonacoElekta Monaco®® VMATVMAT

Philips SmartArcPhilips SmartArc®®

Eclipse RapidArcEclipse RapidArc®®

ProwessProwess®® & & NucletronNucletron MasterPlanMasterPlan®® (Work In Progress)(Work In Progress)


Elekta Ergo++Elekta Ergo++Anatomy based semiAnatomy based semi --inverse planninginverse planning

The shape of each segment within a VMAT arc is The shape of each segment within a VMAT arc is determined by the Beamdetermined by the Beam’’s Eye View (BEV) of targets s Eye View (BEV) of targets and adjacent critical structures.and adjacent critical structures.

After aperture shape is determined, the weight of e ach After aperture shape is determined, the weight of e ach segment is optimized to achieve a desirable dose segment is optimized to achieve a desirable dose distribution.distribution.

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2010 ACMP Annual Meeting, San Antonio2010 ACMP Annual Meeting, San Antonio 2010 ACMP Annual Meeting, San Antonio2010 ACMP Annual Meeting, San Antonio

Ergo++ Ergo++ -- Pancreas Pancreas -- Case 1Case 1


Ergo++ Ergo++ -- Pancreas Pancreas -- Case 1Case 1


Ergo++ Ergo++ -- GBMGBM


Monaco is an IMRT planning system originally developed at the University of Tubingen.

VMAT planning is a work in progress.

An arc sequencer was used to convert the optimized fluence maps into a single VMAT arc.

Dose calculation uses Monte-Carlo dose engine.

Elekta MonacoElekta Monaco



PTV1 (60 Gy), PTV2 (57 Gy), and PTV3 (54 Gy).

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Elekta Monaco


Philips SmartArcPhilips SmartArc

SmartArc is an extension of the current DMPO SmartArc is an extension of the current DMPO functionality in Pinnacle.functionality in Pinnacle.

Designed to work with both Varian and Elekta.Designed to work with both Varian and Elekta.

FDA 510(k) clearance was received in April 09FDA 510(k) clearance was received in April 09

Currently available clinically in PinnacleCurrently available clinically in Pinnacle 33 9.0 9.0


Prostate ExampleProstate Example

1 arc, 180 cGy/fraction

480 monitor units, 1.75 minutes


H&N ExampleH&N Example

PTV70

PTV60

PTV66

2 arcs, 512 monitor units

4 min. 7 sec. delivery time2010 ACMP Annual Meeting, San Antonio2010 ACMP Annual Meeting, San Antonio

Solid = SmartArc Dashed = Tomotherapy

H&N ExampleH&N Example

PTV70

PTV60

PTV66

CordLt. Parotid

Rt. Parotid

PTV50

Lt. Parotid

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Comparison of Comparison of different inverse planning approaches different inverse planning approaches


A Pancreas CaseA Pancreas Case

Anatomy-based Fluence-based Aperture-based


A Pancreas CaseA Pancreas Case

Thick Solid lines: Anatomy-basedThin Solid lines: Fluence-basedDashed lines: Aperture-based


A H&N CaseA H&N Case

Thin Solid lines: Anatomy-basedThick Solid lines: Fluence-basedDashed lines: Aperture-based


Which Planning System to Choose?Which Planning System to Choose?

The anatomyThe anatomy--based Inverse planning is easy to plan and based Inverse planning is easy to plan and is capable of generating conformal dose distributio ns for is capable of generating conformal dose distributio ns for simple cases. However, it may fail to provide a sol ution simple cases. However, it may fail to provide a sol ution for more complex cases.for more complex cases.

Both fluenceBoth fluence--based and aperturebased and aperture--based inverse planning based inverse planning approaches can achieve comparable plan qualities fo r approaches can achieve comparable plan qualities fo r most of the clinical cases.most of the clinical cases.


VMAT Commissioning and QAVMAT Commissioning and QA

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Elekta VMAT CommissioningElekta VMAT Commissioning

J.L. Bedford and A.P. Warrington, Commissioning of Volumetric Modulated Arc Therapy (VMAT). IJROBP 73 (2) pp. 537-545 (2009)


VMAT Commissioning testsVMAT Commissioning tests

Beam flatness and symmetryBeam flatness and symmetry

MLC leaf calibrationMLC leaf calibration

Sliding window doseSliding window dose

Rotational accuracyRotational accuracy

Beam interruption and terminationBeam interruption and termination


VMAT Machine Specific QAVMAT Machine Specific QA

MLC leaf positionMLC leaf position

Gantry angleGantry angle

Dose rateDose rate

The three major variables during VMAT deliveryThe three major variables during VMAT delivery


A special VMAT plan with specific MLC A special VMAT plan with specific MLC leaf motion patterns and dose rate leaf motion patterns and dose rate

variations was developed to check all variations was developed to check all three major variables three major variables

Gantry continue rotates while the MLC leaves are moving.

Dose rate also varies while gantry is rotating.

The plan was measured using a MatriXX 2D ion chamber inserted in a MULTICube phantom.

The data were recorded in movie mode with 0.1 second sampling time.


The VMAT plan for machine QAThe VMAT plan for machine QA

The theoretical dose distribution calculated using convolution/superposition dose engine in Pinnacle. The calculation was done w ith 1° gantry spacing.


How to check the variablesHow to check the variables

MLC leaf motion: The projection position of the tip for MLC leaf motion: The projection position of the tip for each MLC leaf on the MatriXX device can be used to each MLC leaf on the MatriXX device can be used to determine the MLC leaf motion accuracy.determine the MLC leaf motion accuracy.

Gantry angle: The projection width of the 1cm gap Gantry angle: The projection width of the 1cm gap between MLC leaves on the MatriXX device can be use d between MLC leaves on the MatriXX device can be use d to determine the gantry angle.to determine the gantry angle.

Dose rate: The absolute dose measured in the open Dose rate: The absolute dose measured in the open area from each 0.1s sample can be used to determine area from each 0.1s sample can be used to determine the actual dose rate.the actual dose rate.

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The measurement resultThe measurement result

The measurement was interpolated into 1mm dose grid using cubic splineinterpolation method. The sample time is 0.1 second .


QA ResultsQA Results

The standard deviation of the gantry angle error is 1.0° with a maximum error of 2.6°. The standard deviation of the leaf position error i s 1.1mm with a maximum error of 3.1mm in this case.The mean error of the dose rate is 2.7 MU/minutes o r 3.2% in relative mode.


VMAT patient specific QAVMAT patient specific QA


VMAT plan QA methodsVMAT plan QA methods

Film & ion chamber.Film & ion chamber.

2D diode array (2D diode array (MapcheckMapcheck in in MapPhanMapPhan phantom)phantom)

2D ion chamber array (MatriXX in MULTICube phantom)2D ion chamber array (MatriXX in MULTICube phantom)

Other 2D/3D diode system (Delta4 & Other 2D/3D diode system (Delta4 & ArcCheckArcCheck) )


Film & Ion ChamberFilm & Ion Chamber

A stack of solid water phantom with a total thickne ss of 15cm.A stack of solid water phantom with a total thickne ss of 15cm.A 0.6cc farmer chamber was inserted at the depth of 10cm.A 0.6cc farmer chamber was inserted at the depth of 10cm.A film was sandwiched 1cm above the ion chamber. A film was sandwiched 1cm above the ion chamber.


2D Diode Array2D Diode Array

A MapCheck device inserted into a A MapCheck device inserted into a MapPhanMapPhan solid water phantomsolid water phantom

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2D ion Chamber Array 2D ion Chamber Array

An IBA MatrixxAn IBA Matrixx®® 2D ion2D ion--chamber array inserted in a MULTICube phantom.chamber array inserted in a MULTICube phantom.


ScandidosScandidos DeltaDelta 44

A cylinder-shaped plastic phantom with 2 imbedded orthogonal crossing detector planes.

1069 diode detectorsDose is recorded in 2 planes and a 3D dose is reconstructed for comparison with the QA plan.


1386 diode detectors arranged in cylindrical geomet ry1386 diode detectors arranged in cylindrical geomet ry

Measures entrance and exit doseMeasures entrance and exit dose

The QA can be done in composite or per control poin t The QA can be done in composite or per control poin t

Arc Check Arc Check –– Sun NuclearSun Nuclear


A HeadA Head --&&--Neck CaseNeck Case

A threeA three--arc headarc head--&&--neck case with 498 MU neck case with 498 MU to deliver 200 cGy per to deliver 200 cGy per fractionfraction

The delivery time for The delivery time for this case is 5.6 minutesthis case is 5.6 minutes


Film & Ion Chamber QA resultFilm & Ion Chamber QA result

The Gamma analysis passing rate in this case is 96. 4%The Gamma analysis passing rate in this case is 96. 4%The measured ion chamber dose was 0.2% more than th e planned oneThe measured ion chamber dose was 0.2% more than th e planned one

measurement plan


MapCheck in MapCheck in MapPhanMapPhan QA resultQA result

With 3% and 3mm criteria, the gamma analysis passin g rate is 96.With 3% and 3mm criteria, the gamma analysis passin g rate is 96.5%5%Dose threshold in gamma analysis is 10%Dose threshold in gamma analysis is 10%

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Dose Rate DependencyDose Rate Dependency

0.975

0.980

0.985

0.990

0.995

1.000

1.005

0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00 400.00 450.00 500.00

dose rate (MU/minute)

rela

tive

dose

res

pons

e

Mapcheck diode

MatriXX ion chamber

The variation of dose response with the dose rate c an reach up to 2.5% for MapCheck diode.


Calibrate MapCheck with medium dose rateCalibrate MapCheck with medium dose rate

Gamma passing rate increased to 98.8%Gamma passing rate increased to 98.8%

Dose calibration was performed at 224 MU/Min


Angular dose response of MapCheck Angular dose response of MapCheck diodediode

Significant variation of the dose response can be f ound when theSignificant variation of the dose response can be f ound when the incidence incidence beam angle is parallel to the detector plane.beam angle is parallel to the detector plane.Each diode in MapCheck may have different angular d ose response Each diode in MapCheck may have different angular d ose response curve. curve.

-10.0

-5.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

-180 -120 -60 0 60 120 180Gantry Angle

Per

cent

Err

or (%

)

180°°°°

90°°°°

0°°°°

-90°°°°

Couch

detector array& phantom

-180°°°°

phantom setup MapCheck Diode MatriXX ion chamber

-10.0

-5.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

-180 -120 -60 0 60 120 180

Gantry Angle

perc

ent e

rror

(%

)


MatriXX QA resultsMatriXX QA results

measurement plan

With 3% and 3mm criteria, the passing rate is 98.2% for this corWith 3% and 3mm criteria, the passing rate is 98.2% for this cor onal sliceonal sliceNo dose threshold was applied in gamma analysis. No te the passinNo dose threshold was applied in gamma analysis. No te the passing rate reduces to 97.1% g rate reduces to 97.1% if a 10% threshold is applied. if a 10% threshold is applied.


ArcCheckArcCheck QA resultQA result

Gamma analysis passing rate is 95.2% for this case.


SummarySummary

VMAT has been introduced into daily clinic. As a ro tational apprVMAT has been introduced into daily clinic. As a ro tational approach oach to IMRT, VMAT can provide highly conformal dose dis tributions wito IMRT, VMAT can provide highly conformal dose dis tributions with th excellent delivery efficiency.excellent delivery efficiency.

Various commercial planning systems are available f or VMAT Various commercial planning systems are available f or VMAT planning. For relative simple cases, all systems ca n provide higplanning. For relative simple cases, all systems ca n provide high h plan quality. However, the anatomyplan quality. However, the anatomy--based semibased semi--inverse planning inverse planning algorithm may fail to provide a clinical acceptable plan for moralgorithm may fail to provide a clinical acceptable plan for more e complicated headcomplicated head--&&--neck cases.neck cases.

The gantry angle, MLC leaf position, and dose rate are three majThe gantry angle, MLC leaf position, and dose rate are three major or variables during VMAT delivery that need to be chec ked as part ovariables during VMAT delivery that need to be chec ked as part of f machine specific QA. Various systems can be used fo r VMAT machine specific QA. Various systems can be used fo r VMAT patientpatient--specific QA provided that users know the limits of each specific QA provided that users know the limits of each system.system.

1 volumetric modulated arc therapy - clinical implementation outline

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