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ArcCHECKTM
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TPS, Linac, MLC. Ability to measure. Gantry angle. Leaf end ... TPS, Linac, MLC. No issues with secondary dose algorithms or black boxes. Ability to measure ... – PowerPoint PPT presentation
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Title: ArcCHECKTM
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ArcCHECKTM
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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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Discussions Information Weight
- 0º beam is normal to the array and all
information is weighted equally - 90º 2D reduced to 1D, most information is lost
- Other angles variable weights
- Dosimetric information is over or under-weighted
based on beam angle and field size
0º
90º
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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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DVH Analysis
- Uses existing IMRT QA measurements to generate
the 3D patient dose DVH statistics
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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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No Black Boxes
SNC Transparency
- It is common for the audited system (TPS) and the
auditing system (QA System) to use black box
solutions.
- Sun Nuclear is independent from algorithms to
hardware to software systems. - The Sun Nuclear genetic tree creates healthy
checks and balances for the radiation therapy
ecosystem.
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Caution Shared DNA
- When a QA system shares DNA with a TPS, at some
point one will achieve great comparisons between
similarly wrong datasets, rather than catching
errors with independent QA. The QA device will
not recognize the error coming from the TPS,
because that error will be it's sibling.
TPS
Independent Comparison
Compare And Prove What?
Treatment Plan Calculation
Black Box Calculation Supplier
STOP
Calculation Algorithms
Treatment Machine Supplier
QA System
SNC QA System
QA Calculation
QA Calculation
Data
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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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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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