Download - Delaware Valley 2010
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Treatment time reduction for proton modulated scanning
beams
James Durgin, Derek Dolney, James McDonoughUniversity of Pennsylvania
December 9, 2009Delaware Valley AAPM Young Investigator Symposium
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Treatment Options
Double Scattering Uniform Scanning Modulated Scanning
Distal Conformity ~Equal ~Equal ~EqualProximal Conformity Poor Poor Good
Lateral Conformity Depth dependent Depth dependent Depth dependentDose Uniformity Target dependent Target dependent BestTime Fastest Intermediate Slowest
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Bragg Peak Stacking
Achieving a uniform dose requires many Bragg peaksAt lower energies, range straggling decreases resulting in sharper Bragg peaks
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Beamline Transmission
Reducing proton energy in beam line reduces the rate of protons in nozzle~1% at 100MeV
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Range Shifters, Ridge Filters
Current solution is a range shifterPulls back distal peakIncreases range stragglingNeutron production
Ridge filters could be used in conjunctionSpreads out Bragg peakMinimal degradation of penumbra possible
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Designing a Ridge Filter
GoalsFlat ~1cm area at 100MeVPreserve distal falloffConserve penumbra
ConsiderationsFocused beamMLC, bolus exchangerDedicated nozzle
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Geant4 Simulations
Commonly used for proton modelingSaves on development costsNo beam time issuesCode used for Eclipse commissioning available
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Ridge Filter Shape
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Depth Doses
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Ridge Filter Penumbra
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1-Dimensional Stacking
A simple algorithm was used to test stacking in 1 dimensionSpacing increasedNumber of energy levels decreased
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Eclipse Commissioning
Real test is how Eclipse uses beam dataCommissioning requires depth dose in water, penumbra in air, other machine parameters
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Preliminary Results
Tested a sphere target, d=1.5 cm, in Rando phantom at ~100MeVSimilar dose distrubtions with and without RF
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Preliminary Results
Energy levels from 14 to 5Beam spots from 150 to 122MUs reduced by ~45%
Ridge filter
Unobstructed
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Summary
Modulated scanning is slow at shallow depthsA range shifter is requiredA ridge filter can be constructed to decrease delivery time while preserving much of the beam qualityEclipse commissioning shows fewer energy levels, beam spots, and MUs with similar coverage
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Future Work
Combine range shifter and ridge filterSite specific devicesRefine machine parameters for planningValidate Monte Carlo models
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This work was supported by the US Army Medical Research and Material Command under Contract Agreement No. DAMD17-W81XWH-04-2-0022. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the US Army.
AcknowledgementsJames McDonough
Derek Dolney
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Additional Slides
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Ridge Filter Material
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Penumbra v. Distance of RF
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Penumbra v. Thickness of RF
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Depth Dose at Several Energies
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Penumbra v. Depth
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MLCs with Modulated Scanning
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Penumbra v. Depth