Acknowledgements
RapidArc: Clinical
Implementation
Fang-Fang Yin, PhD
• Team efforts from staff at Duke Radiation
Oncology, especially to Dr. J Chang, Dr. J
O’Daniel for providing slide information
• Technical and financial supports from Varian
Medical Systems
Q. Jackie Wu, PhD
Duke University Medical Center
Clinical Implementation of VMAT
• Fundamentals for RapidArc
• Infrastructure/Installation
• Acceptance testing/commissioning
• Planning
• Delivery
• Quality assurance
Fundamentals for VMAT
• Intensity Modulated arc therapy (VMAT)
– An arc-based approach to IMRT
– To be delivered on a conventional linear
accelerator with a conventional MLC
– During an arc, the leaves of the MLC
move and dose rate changes
continuously as the gantry rotates
• RapidArc is one format of VMAT
1
The Principle of IMRT: Dose Painting
Expected 3-field IMRT
Conventional 3-field RT
Static and Rotational IMRT
VMAT
Static gantry IMRT
Typical dose
distribution
OAR
PTV
OAR
Beam Profile
PTV
Multiple apertures
At each angle
The Format of Cone-Beam IMRT
Static Gantry IMRT
Rotational IMRT
One aperture
At each angle
Volumetric Rotational IMRT Options
• Existing Planning Systems
•
•
•
•
Eclipse (Varian) – Duke choice
ERGO++/Monaco (Elekta)
Pinnacle SmartArc (Philips)
Prowess (Prowess)
• Existing Delivery Systems
• RapidArc (Varian) – Duke choice
• VMAT (Elekta)
• Cone-beam Therapy (Siemens) (WIP)
• Existing QA Systems
Field1 @180o
One of 7 fields
One arc from 179o  181o
Count-clockwise
•
•
•
•
•
Matrixx – Duke choice for routine QA
Film – Duke choice for commission
SunNuclear
Delta 4 – Duke choice for future QA device
Optical Scanner ……
2
Where Are We (Duke)?
• Started investigation in June 2008
– A research RapidArc planning station from Varian
• Clinical installation in October
– Acceptance testing, commissioning, QA programs
– Single arc, no couch rotation, partial arc
• First patient treatment
– December 2008
• New versions in August 2009 and May 2011
Clinical Implementation of RapidArc
• Fundamentals for RapidArc
• Infrastructure/Installation
• Acceptance testing/commissioning
• Planning
• Delivery
• Quality assurance
– Allow multiple arcs, couch rotation, partial blocking, etc.
Infrastructure/Installation
• Staff (dedicated and trained)
• Existing machines:
Clinical Implementation of RapidArc
• Fundamentals for RapidArc
– 21EX machine with 120-leaf millennium MLC
• Infrastructure/Installation
– NovalisTx with 120-leaf HD MLC (SRS, SRT,SBRT)
• Acceptance testing/commissioning
• ARIA version 8.6 or above (v10 now)
• Planning
• Eclipse planning station (hardware and software)
• Delivery
• QA equipment
• Quality assurance
3
Acceptance Testing
• Machine readiness
• Verification of installation against items included in the
purchase order
• Inspections of safety and quality of installation and
components
• VMAT performance
• Testing of functionality of each component and system
performance against specifications.
Acceptance Testing Sample
• Test 1.1: Gantry Angle Calibration
– Tolerance: + 0.5°
• Test 1.2: Isocenter Calibration
– Tolerance: + 1 mm
• Test 1.3: General Arc Dosimetry
– Range: 0.2 MU/° to 5.0 MU/°
– Tolerance: + 1%
• End-to-end testing
• Dry-runs for a few test case from simulation to delivery
Acceptance Testing Sample
Acceptance Testing Sample
• Test 1.4
• dMLC Dosimetry
• 0.5cm MLC slit sliding
over 4 cm range
• Gantry:
0°, 90°, 270°, 180°
• Test 2.1:
• Accuracy of dMLC
position vs. gantry
position
• Tolerance: + 1 mm
• Tolerance: + 2%
(over mean value)
4
Acceptance Testing Sample
Acceptance Testing Sample
• Test 2.2:
• Accuracy of dMLC
position during arc
• Tolerance: + 1 mm
2.1: Picket Fence vs. Gantry Angle (static)
Acceptance Testing Sample
Acceptance Testing Sample
2.1: Picket Fence vs. Gantry Angle (static)
5
Acceptance Testing Sample
Acceptance Testing Sample
• Test 2.3:
• Ability to
accurately detect
MLC position error
• Criteria: detect submillimeter error in
position
2.3: Picket Fence with Errors
Acceptance Testing Sample
• Test 2.4:
• Accuracy of dose
rate and gantry
speed control during
RapidArc
• Tolerance: + 2%
Acceptance Testing Sample
• Test 2.5:
• Ability to control
leaf
speed/position
during RapidArc
• Tolerance: + 2%
6
Acceptance Testing Sample
1.20
1.0
1.18
0.8
Percent Deviation (%)
Relative Dose
Acceptance Testing Sample
1.16
1.14
1.12
Off y-axis : -100 mm
Off y-axis : 0 mm
Off y-axis : 100 mm
1.10
1.08
Gantry speed
vs.
Dose rate
(Tolerance 2%)
1.06
1.04
1.02
-150
-100
-50
0
50
0.4
0.2
0.0
-0.2
-0.4
Variation of gantry speed and dose
rate (tolerance 2%)
-0.6
-0.8
1.00
-200
Off y-axis: -100 mm
Off y-axis: 0 mm
Off y-axis: 100 mm
0.6
100
150
200
Off x-axis Position (mm)
Commissioning
• Validate that VMAT is capable of delivering
radiation beams as good as SG-IMRT could
• Define the limitations of planning optimization,
gantry rotation, beam blocking, couch rotation,
and leaf speed, collimator settings
• Develop treatment process and
documentation
-1.0
-60
-40
-20
0
20
40
60
Off X-axis Position (mm)
Workflow for RapidArc Treatment
Case selection
Immobilization/simulation
Planning/prescription
Quality assurance
Target localization
Treatment/validation
7
Clinical Implementation of RapidArc
Planning - Process
• Fundamentals for RapidArc
• Infrastructure/Installation
• Acceptance testing/commissioning
• Planning
• Delivery
• Quality assurance
SG-IMRT
Planning - Preparation
• Site-specific, for each site
– 10 cases from previous IMRT
RapidArc
Planning - Strategy
• Selected site-specific planning strategy
– Develop RapidArc plan with different options
– 1 arc: prostate only, prostate bed, prostate+SV,
brain lesions
– Comparison between IMRT vs. RapidArc
– 2 arcs: prostate+SV+LN, spinal, brain lesions
• Constraint/optimization
– Optimization algorithm
– Constraints sensitivity
– Multiple arcs: Head and neck, brain lesions, analrectal
– Partial arcs: partial breast, liver, …
8
Planning - Optimization
Planning – Quality and Efficiency
• Key challenge
– interconnectivity of the beam shapes within consecutive
VMAT gantry positions
• Constraints
– Target and normal structures
– Mechanicals
• Optimization algorithms
• MLC segments
– Number of segments: IMRT  RapidArc
– Plan quality is comparable if same segments
– More segments: slow gantry rotation for RapidArc
– More segments: long treatment time
• Planner experience
– More parameters
– Understand algorithm
– Aperture based objectives and algorithms
– Understand limitations
Planning - Logistics
• Training – multiple people involved in the
planning
• Gaining experience
Clinical Implementation of RapidArc
• Fundamentals for RapidArc
• Infrastructure/Installation
• Acceptance testing/commissioning
• Develop planning protocols
• Planning
• Last ~ 3 months before patients start
• Delivery
• Quality assurance
9
Delivery – Sample Parameters
Delivery - Tolerances
• MLC leaf motion
• Leaf motion limit: 2.5 cm/s, 5 mm/degree
• Dose rate and gantry rotation speed
• One arc = one field
• MU, doserate, gantry speed linked
• Larger MU  max doserate  varying gantry speed
• Smaller MU  max gantry speed  varying doserate
• Middle  varying gantry speed and doserate
RapidArc Delivery Limits
• Variable gantry speed
– 0.5 – 5.6 degree/sec
• Variable dose rate
– 0 – 600 MU/min (0 -1000 Novalis Tx)
• Variable dose per degree
– 0.2 – 20 MU/degree
• Variable MLC speed
– 0 –2.5 cm/s
Delivery - Efficiency
• Plan quality
• The quality of plan  number of apertures
• Single arc – 177 apertures
• Complexity structures:
• more apertures/arcs
• multiple arcs
• Delivery time
• Single arc – less time (< 2 mins) but sometimes
inferior quality
• Multiple arcs – better quality but longer time
10
Delivery – Treatment Time
Delivery – Partial Arc
• Mechanical collision
• Treatment time = Patient set-up time + Delivery time
• If isocenter is close to
center
• Delivery time=beam-on time+between beam=on time
• Patient setup time: no reduction
• full arc
• Beam-on time: 20-60% reduction (less MUs)
• If isocenter is close to
peripheral
• Between beam-on time:
• 100% saving for single arc
• partial arc
• 20-60% saving for multiple arcs
Partial RapidArc for Liver SBRT
• Partial blocking is
also available
Multiple Arcs vs. Single Arc
Single arc
RapidArc MU = 714
IMRT Total MU = 1572
Multiple arcs
Time: 1.3 min
11
VMAT For Large Size PTV
• Large field size -> sometimes IMRT beam has triple
beam splits
VMAT For Large PTV
3 Arcs, 1000 degree rotation
17cm Field Size << PTV in some
directions
• Multi-sections (parts) of the PTV, large variation of
PTV shape, OARs and their constraints
• Beam orientation selection is part of IMRT planning,
is often not used for RapidArc (i.e. full arc)
VMAT For Large Size PTV
IMRT
VMAT17cm
VMAT For Large PTV
IMRT
VMAT17cm
12
VMAT For Large PTV
IMRT
VMAT26CM
VMAT17cm
VMAT For Large PTV
VMAT 17cm
Field Size Effect On VMAT
Planning Quality
PTV Hot Spot (D1%)
VMAT23cm
160
Collimator 30
150
Collimator 45
140
D1% (%)
VMAT17cm
VMAT For Large PTV
130
120
110
100
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
Projected Field Size X (cm)
13
VMAT For Head-and-Neck
VMAT For Head-and-Neck
VMAT
IMRT
VMAT
Field Thru
Shoulder
Field Thru
Shoulder
VMAT For Head-and-Neck
VMAT
RapidArc For Head-and-Neck
IMRT
Rt Parotid
Lt Parotid
Pharynx
Oral Cavity
Cord
14
VMAT For Head-and-Neck
Clinical Implementation of RapidArc
• Fundamentals for RapidArc
• Infrastructure/Installation
• Acceptance testing/commissioning
Segments Thru Shoulder
• Planning
• Delivery
• Quality assurance
Quality Assurance
• The QA program for the VMAT is similar to SG-IMRT
in principle but with different measurement
approaches due to its dynamic nature that, during
Quality Assurance
• The QA program: validate the functionality
and performance of accepted features
VMAT delivery,
– MLC leaves are moving
• For each planned delivery
– Gantry is rotating
– Patient specific QA
– Dose rate is changing
– Machine specific QA
15
Quality Assurance
• Machine specific QA
– accuracy of the MLC leaf positions during VMAT
delivery
– ability of the system to accurately vary the dose
rate and gantry speed during VMAT delivery
– ability of the system to accurately vary the MLC
leaf speed during VMAT delivery
• Tolerances: Acceptance baselines
Patient Specific QA
• Hybrid QA technique
– Plan to phantom
– Dose measurement to phantom
• Rotational nature
– Not to single plan
• Phantoms
• Instruments
– Ion chamber
– 2-D array (ion chamber, diodes, film, …)
Machine QA Chart
• Daily
– Standard linac QA
– Standard MLC QA
– Rotational delivery of dose to an ion chamber phantom
• Monthly
– Leaf motion
– Gantry rotation
– Dose output
• leaf motion
• gantry motion
• dose rate changes
Patient Specific QA
• Data analysis
– Multiple planes (axial, coronal, sagittal)
– Profiles
– Points
– Gamma analysis
• Collision check
– Before patient on the couch
– When patient on the couch
16
RapidArc QA vs. IMRT QA
• More complex treatment delivery
– Varying gantry angle, gantry speed, dose rate, and
MLC leaf motion
• ImSure does not calculate dose for RapidArc
delivery
• Current IMRT technique: Portal dosimetry
• RapidArc technique: Ion chamber, film, and
Matrixx
QA Measurements
• Ion chamber
– Absolute dose: (meas – calc) / calc < 3%
• Film (coronal, sagittal, and axial planes)
– Optional
• Matrixx (coronal and sagittal planes)
• 3-6 hrs/patient
“Gold Standard” QA Tools
Ion Chamber
• Equipment
– 0.13cc or 0.01cc ion
chamber
Ion Chamber
Film
• Calibration
– 10x10cm2, 100SSD, depth
= dmax, 200MU
– cGy/nC correction factor
• RA delivery
– Center of 30cm x 30cm x
20cm solid water
phantom
– Compare to Eclipse
calculation
• 39 VMAT plans
17
Verification with “Gold Standard” QA
Film
• Equipment
– Kodak EDR2 film
– OmniPro ImRT
• Calibration
– 12 2cm x 2cm squares
– 0 – 300cGy
• RA delivery
– MultiCube (IBA dosimetry)
– Coronal, sagittal, and axial planes
– Compare to Eclipse calculation
• Ion chamber:
– Median: +1.7%
– Range: -0.9% - 2.8%
• Film
– 24/24 > 93% passing rate
– 23/24 > 95% passing rate
– 20/24 > 97% passing rate
– Gamma analysis
• 8 MAT plans
Ion Chamber vs. Eclipse
Result: Axial Film vs. Eclipse
Ion chamber array vs. Eclipse
Eclipse
3%, 3mm DTA, 5% threshold
Film
18
Film vs. Eclipse
Film vs.
Eclipse
Film Film
vs.vs. Eclipse
Eclipse
100
100
95
85
80
75
70
Coronal
Sagittal
Axial
65
3%, 3mm DTA, 5% threshold
% Pixels Passing Gamma (<1)
90
85
80
75
70
Coronal
Sagittal
Axial
65
3%, 3mm DTA, 5% threshold Sagittal and Coronal, 40% threshold Axial
3%, 3mm, axial thresholds up to 40%
1
2
3
14
4
15
5
23
6
24
7
32
8
Plan #
Validation of 2D Ion Chamber Array
60
1
2
3
– 0.07 cm3 sensitive volume
– 0.4cm diameter
• 24 x 24 cm2 grid
• 7.6mm spacing
• Automatic temperaturepressure correction
15
5
23
6
24
7
32
8
Plan #
Angular Dependency:
Future solution from IBA:
Gantry angle sensor
Apply correction
factor to each ion
chamber based on
angularity
+2.2% 15x
• MatriXX Evolution (IBA
Dosimetry)
• 1020 ionization chambers
14
4
+3.0% 6x
+2.0% 15x
+2.8% 6x
Back
60
Front
% Pixels Passing Gamma (<1)
95
90
-1.8% 15x
-3.5% 6x
Measured/Calculated (%)
Herzen et al., PMB 2007; 52: 1197-1208
+3.2% 15x -1.7% 15x
+3.7% 6x -2.0% 6x
19
Results Patient Specific QA
Matrixx QA
%Pixels Passing (Gamma <= 1)
Matrixx vs Eclipse
100
98
96
94
92
90
MatrixxCoronal
MatrixxSagittal
3%, 3mm, axial thresholds up to 5%
88
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
RapidArc (Plan #)
Film vs. Ion
Chamber
Film vs.
Ion Chamber ArrayArray
1: IonEclipse
Chamber vs. Eclipse
Matrixxvs.
vs. Eclipse
Ion Chamber Fig.
vs.
& and
ICA
Eclipse
100
6%
IC
IC Array
%Difference from Eclipse Calculation
2%
0%
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
-2%
%Pixels Passing Gamma (<1)
98
4%
96
94
92
90
Coronal
Sagittal
-4%
Brain
Prostate
Bed
Prostate
-6%
Plan #
Prostate
+ SV
Spine
Gamma = 3%, 3mm, 5% threshold
88
0
1
1
2
33
4
14
155
6
23
7
24
8
32
9
Plan #
20
Effective vs. Efficient
• Stage 1: Intensive QA
– Ion chamber, film in 3 planes, ion chamber array in
2 planes, 3D polymer gel dosimetry
• Stage 2: Rigorous QA
– Ion chamber, ion chamber array in 2 planes
• Stage 3: Effective and Efficient QA
– Ion chamber, ion chamber array in 1 plane
– Ion chamber array only
Effective vs. Efficient
• When implementing a new technology
– Perform intensive patient-specific QA for the first
group of patients
– Rely on QA “gold standards”
– 3D QA very useful
– Use “gold standard” QA technology to transition to
newer QA devices
• Goal: Effective QA
Effective vs. Efficient
Preparation
Delivery
Ion chamber – 1st
15
15
Analysis
5
Film – 1st
15
20
20
5
Ion chamber array – 1st
15
15
Ion chamber – additional
15
7
5
Film – additional
15
10
10
Ion chamber array –
additional
15
7
5
IC + 3 Film + 2 ICA
90
77
55
IC + 2 ICA
45
37
15
IC + ICA
30
30
10
Conclusion
• RapidArc is one format of rotational IMRT for dose
painting
• Implementation of RapidArc requires careful
planning, testing, and verifications.
• Thoroughly testing and commissioning are
necessary prior to patient treatment
• QA is a critical step, always compare with static field
IMRT plan in the early phase
• RapidArc should be judged by its
accuracy, safety, efficiency, applicability, integration
, and adaptation
21
Thank you for your attention
22