Treatment time reduction for proton modulated scanning

beams

James Durgin, Derek Dolney, James McDonoughUniversity of Pennsylvania

December 9, 2009Delaware Valley AAPM Young Investigator Symposium

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

Bragg Peak Stacking

Achieving a uniform dose requires many Bragg peaksAt lower energies, range straggling decreases resulting in sharper Bragg peaks

Beamline Transmission

Reducing proton energy in beam line reduces the rate of protons in nozzle~1% at 100MeV

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

Designing a Ridge Filter

GoalsFlat ~1cm area at 100MeVPreserve distal falloffConserve penumbra

ConsiderationsFocused beamMLC, bolus exchangerDedicated nozzle

Geant4 Simulations

Commonly used for proton modelingSaves on development costsNo beam time issuesCode used for Eclipse commissioning available

Ridge Filter Shape

Depth Doses

Ridge Filter Penumbra

1-Dimensional Stacking

A simple algorithm was used to test stacking in 1 dimensionSpacing increasedNumber of energy levels decreased

Eclipse Commissioning

Real test is how Eclipse uses beam dataCommissioning requires depth dose in water, penumbra in air, other machine parameters

Preliminary Results

Tested a sphere target, d=1.5 cm, in Rando phantom at ~100MeVSimilar dose distrubtions with and without RF

Preliminary Results

Energy levels from 14 to 5Beam spots from 150 to 122MUs reduced by ~45%

Ridge filter

Unobstructed

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

Future Work

Combine range shifter and ridge filterSite specific devicesRefine machine parameters for planningValidate Monte Carlo models

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

Additional Slides

Ridge Filter Material

Penumbra v. Distance of RF

Penumbra v. Thickness of RF

Depth Dose at Several Energies

Penumbra v. Depth

MLCs with Modulated Scanning

Penumbra v. Depth