ArcCHECK

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ArcCHECK
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Outline

• The QA Challenge for Rotational Beams
• Limitations of existing 2D approaches
• What is 3D, 4D?
• ArcCHECK
• Description, Applications
• Features
• ArcCHECK versus competition
• Key benefits of ArcCHECK
• FAQ

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QA Challenge for Rotational Beams

• Modern technologies are becoming rotational.
• (RapidArc, VMAT, TomoTherapy, IMAT)
• Rotational beam delivery creates a challenge for
  patient specific QA.
• An ideal QA tool would be 3D but this is not
  always practical.

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What is 3D?

• Is this 3D?
• No
• A 2D detector plane designed for IMRT QA

• Is this 3D?
• No
• Two orthogonal 2D detector planes designed for
  IMRT QA

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The Future in 3D

• Make the detector plane
• coherent to the beam

3D

• Is this 3D?
• Yes!

An isotropic 3D array is defined by the detector
geometry, not just by the phantom shape around
the detectors!
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Key Features

• Designed for Helical Arc Delivery
• RapidArc, TomoTherapy, VMAT
• Consistent and coherent measurement geometry
  regardless of gantry angle
• 1386 diodes in a helical geometry
• This detector orientation is patent pending
• 21cm diameter, 21cm length
• 1cm spacing, 2.9cm depth
• Pulse by pulse measurement
• 4th Dimension Time
• 50ms update frequency

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Coherent Delivery

• Detectors remain normal to beam surface
• Measure entrance and exit dose
• Result is a composite dose for entire delivery
• Center cavity accommodates inserts

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Applications

• Fast plan QA
• Composite and real-time measurement
• Find failure mechanisms
• TPS, Linac, MLC
• Ability to measure
• Gantry angle
• Leaf end position
• Dose
• Time synchronized analysis
• Routine machine QA, imaging QA, setup QA
• RapidArc, VMAT, helical delivery commissioning

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Data Display

• ArcCHECK dose unrolls like a world map
• ArcCHECK mathematically extracts same dose from
  TPS
• ArcCHECK performs comparisons

Unroll ArcCHECK Dose
Unroll TPS Dose
Compare!
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QA Failure Mechanisms

• What if there is a failure of the QA comparison?
• Find failure mechanism
• A potential problem to be aware of
• How do you find the failure mechanism if you
  cannot tell if the error is in the QA dose
  algorithm or in the TPS dose algorithm?
• With ArcCHECK there is no QA dose algorithm!
• Focus on measurements, easier to find failure
  mechanisms.
• How to find failure mechanism? MLC, angle, dose,
  plan? They all vary.
• With ArcCHECK we know time, gantry angle, MLC
  leaf ends and of course dose
• This allows one to verify delivery data at each
  sub-segment against a Varian file

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Composite vs. Control Point

• Composite
• The entire treatment dose shell consisting of all
  control points
• Typical rotational QA will be composite
• Control points
• Sub-sections of the treatment dose shell
• Up to 177 control points on a RapidArc delivery
• Tomotherapy does not use control points
• ArcCHECK can measure composite, individual
  control points, and ranges of control points
• 50ms update speed of ArcCHECK enables fast dose
  data parsing
• Benefits of control point QA
• If there is a problem with composite, then drill
  down to evaluate individual control points
• Use control point analysis to help improve
  treatment planning process

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HeliGridTM

• Detectors do not overlap from a BEV perspective
• Benefit is increased detector density
• Each detector row is offset, creating what can be
  called a helical or spiral effect, hence
  HeliGridTM (hee li grid)

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Diode Benefits for Rotational QA

• Reproducibility
• Short term /- 0.15 (15 consecutive 60 cGy
  fields)
• Long term /- 0.2 (9 month period)
• Sensitivity change lt 0.5/kGy at 6MV, 1.5/kGy
  at 10 MeV
• User calibrated in only 15 minutes (typically
  every 12-18 months)
• Sometimes, smaller is better
• More than 4500 times smaller than ion chambers
• Allow TRUE point to point comparison with the TPS
  calculated dose
• Offer 10 times or more sensitivity than ion
  chambers despite small size
• Measure in Absolute Dose with no warm-up time
  required

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Gantry Angle Measurement
source

• Early research shows ArcCHECK can determine
  gantry angle to within 1º with 2cm spacing on
  prototype
• This will improve with 1cm spacing and refinement
  of the technique
• This should get to at least 0.5º, and perhaps
  finer
• This is accomplished with ray tracing
• Measure entrance and exit dose with leaf
  positions to determine beam angle

MLC
MLC
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World Map

• Think of a world map
• This concept is similar to ArcCHECK
• The detectors are wrapped around the phantom
  and irradiated.
• The result is a data file that is unwrapped like
  a world map

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Cavity Plug

• Cavity plug addresses desire to have measurement
  on CAX
• Standard plug will have insert that accommodates
  different detectors

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At SNC, QA Independence

• SNC Software
• SNC solutions are independent of planning and
  delivery vendors, assuring proper checks and
  balances

• SNC Data
• SNC data files are open format for easy export
  and independent analysis
• SNC files include all relevant data
• Dose, Normalized, Corrected, Raw, Offset,
  Calibration

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One 2D Array Two 2D Arrays


Sagittal
Coronal
Equivalent
A 2D array can generate two orthogonal dose
distributions in conventional coronal and
sagittal orientations.
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Competitive Comparison

• ScandiDos Delta 4
• Detector quantity 1069
• True 3D isotropic cylindrical design No
• Weight 27 kg
• Easy to use 4 cable connections
• Secondary calculation Optional

• SNC ArcCHECK
• Detector quantity 1386
• True 3D isotropic cylindrical design Yes
• Weight 14 kg
• Easy to use Single cable connection
• Secondary calculation 2010

• SNC Advantage
• Only ArcCHECK is truly 3D in design
• Only ArcCHECK is specifically designed for arc /
  rotational modalities
• ArcCHECK has 30 more detectors, is half the
  weight, and has only one cable connection making
  the ArcCHECK easier to setup and use

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Competitive Comparison
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ArcCHECK Key Benefits

• Fast plan QA
• Composite and real-time measurement
• Find failure mechanisms
• TPS, Linac, MLC
• No issues with secondary dose algorithms or black
  boxes
• Ability to measure
• Gantry angle
• Leaf end position
• Dose
• Time synchronized analysis
• Routine machine QA, imaging QA, setup QA
• RapidArc , VMAT, helical delivery commissioning
• Planned future DVH analysis

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FAQ

• Is 1cm detector spacing sufficient?
• Yes. Testing has shown that spacing of only 2cm
  is sufficient to detect gantry angle and setup
  errors.
• Why are there not detectors in the middle, or on
  CAX?
• First, they are not necessary from a QA and
  Dosimetry perspective. Entrance and exit dose
  will indicate a problem just as well as CAX dose
  will.
• Second, permanent interior detectors would
  complicate the design, add to the cost, and
  result in a non-homogenous interior design.
• Third, permanent interior detectors would add to
  the setup complexity by increasing weight and
  number of cable connections.
• Can I add a detector to the middle, or on CAX?
• Yes, the ArcCHECK Cavity Plug option will enable
  this.

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Thank you, Questions?