This document discusses using ridge filters to reduce treatment time for proton modulated scanning beams. Ridge filters can spread out the Bragg peak to allow fewer energy levels and beam spots while maintaining dose uniformity and distal conformity. Simulations show a ridge filter constructed to provide a flat 1cm area at 100MeV preserved the distal falloff and penumbra. Preliminary results commissioning the technique in Eclipse planning show treatment time could be reduced by around 45% with similar dose distributions using fewer energy levels, beam spots and monitor units. Further work is needed to refine machine parameters and validate models.

1. Treatment time reduction for
proton modulated scanning
beams
James Durgin, Derek Dolney, James McDonough
University of Pennsylvania
December 9, 2009
Delaware Valley AAPM Young Investigator Symposium

2. Treatment Options
Double Scattering Uniform Scanning Modulated
Scanning
Distal Conformity ~Equal ~Equal ~Equal
Proximal Conformity Poor Poor Good
Lateral Conformity Depth dependent Depth dependent Depth dependent
Dose Uniformity Target dependent Target dependent Best
Time Fastest Intermediate Slowest

3. Bragg Peak Stacking
Achieving a uniform
dose requires many
Bragg peaks
At lower energies,
range straggling
decreases resulting
in sharper Bragg
peaks

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

5. Range Shifters, Ridge Filters
Current solution is a Ridge filters could be
range shifter used in conjunction
Pulls back distal Spreads out Bragg
peak peak
Increases range Minimal degradation
straggling of penumbra
Neutron production possible

6. Designing a Ridge Filter
Goals
Flat ~1cm area at 100MeV
Preserve distal falloff
Conserve penumbra
Considerations
Focused beam
MLC, bolus exchanger
Dedicated nozzle

7. Geant4 Simulations
Commonly used for
proton modeling
Saves on
development costs
No beam time issues
Code used for Eclipse
commissioning
available

8. Ridge Filter Shape

9. Depth Doses

10. Ridge Filter Penumbra

11. 1-Dimensional Stacking
A simple algorithm
was used to test
stacking in 1
dimension
Spacing increased
Number of energy
levels decreased

12. Eclipse Commissioning
Real test is how Eclipse uses beam data
Commissioning requires depth dose in water,
penumbra in air, other machine parameters

13. Preliminary Results
Tested a sphere target, d=1.5 cm, in Rando
phantom at ~100MeV
Similar dose distrubtions with and without RF

14. Preliminary Results
Energy levels from 14 to 5 Ridge
filter
Beam spots from 150 to 122
MUs reduced by ~45%
Unobstructed

15. Summary
Modulated scanning is slow at shallow depths
A range shifter is required
A ridge filter can be constructed to decrease
delivery time while preserving much of the
beam quality
Eclipse commissioning shows fewer energy
levels, beam spots, and MUs with similar
coverage

16. Future Work
Combine range shifter and ridge filter
Site specific devices
Refine machine parameters for planning
Validate Monte Carlo models

17. Acknowledgements
James McDonough
Derek Dolney
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.

18. Additional Slides

19. Ridge Filter Material

20. Penumbra v. Distance of RF

21. Penumbra v. Thickness of RF

22. Depth Dose at Several Energies

23. Penumbra v. Depth

24. MLCs with Modulated Scanning

25. Penumbra v. Depth