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3 Forrest Iandola Computational Geometry Compensators Medical Physics in 30 Seconds Goal: kill cancer with radiation Deliver radiation with protons, photons, other particles, or ions Monte Carlo simulation of proton therapy beams is an up-and-coming field
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Representing Range Compensators with Computational Geometry in TOPAS
Forrest Iandola1,2 and Joseph Perl1
1 SLAC National Accelerator Laboratory2 University of Illinois at Urbana-Champaign
2Forrest Iandola
Computational Geometry Compensators
Overview
• Medical Physics in 30 Seconds• Introduction to TOPAS• What is a range compensator?• Subtraction Solid geometry• Modeling compensators with Subtraction Solids• Approximation with polyhedrons for (potentially)
faster performance
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Medical Physics in 30 Seconds
• Goal: kill cancer with radiation• Deliver radiation with protons, photons,
other particles, or ions• Monte Carlo simulation of proton therapy
beams is an up-and-coming field
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Computational Geometry Compensators
Introduction to TOPAS
TOPAS (Tool for Particle Simulation)
• TOPAS = Monte Carlo simulation of radiation therapy beamlines
• User can easily customize beamline for specific treatment facilities
• Uses Geant4 for the “real” physics
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What is a Range Compensator?
• A radiation therapy beamline collimates the beam and produces a specific energy spread
• Range compensator produces an energy spread• Construction: drill a number of holes out of a
cylinder of lucite• Each drill hole may have a unique depth• “The thickness of the Lucite [plastic] will
proportionally reduce the depth [energy] of the protons”1
1 http://neurosurgery.mgh.harvard.edu/protonbeam/
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What is a Range Compensator?
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Subtraction Solids
• Geant4 supports boolean solid combinatorial geometry– Subtraction solids– Union solids
• It’s as simple as newSolid = Solid1 - Solid2• Overlap among subtracted solids is
acceptable• Solids can be recursively subtracted
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Compensator with Subtraction Solids
Compensator comprised of a bigCylinder with n holes subtracted:
newSolid1 = bigCylinder - smallCylinder1newSolid2 = newSolid1 - smallCylinder2…Compensator = newSolid(n-1) - smallCylinder(n)
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Compensator with Subtraction Solids
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Approximation for Performance Gains
• Approximate the drill holes with a collection of hexagons
• Lack of overlap among hexagons allows us to model all hexagons as a single polyhedron
• Future work: evaluate performance benefits (and accuracy reduction) with polyhedron method
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Computational Geometry Compensators
Approximation for Performance Gains
Subtraction Solid Polyhedron
12Forrest Iandola
Computational Geometry Compensators
Approximation for Performance Gains
• Future work: evaluate performance benefits (and accuracy reduction) with polyhedron method
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Computational Geometry Compensators
Acknowledgements
• Harald Paganetti (Massachusetts General Hospital and Harvard University)
• Jan Schuemann (Massachusetts General Hospital and Harvard University)
• Jungwook Shin (UC San Francisco)• Bruce Faddegon (UC San Francisco)• DOE and NIH for generous support
Contact: [email protected]