Unconventional Acceleration Systems for Proton Radiotherapy

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1 Unconventional Acceleration Systems for Proton Radiotherapy Thomas Rockwell Mackie Emeritus Professor University of Wisconsin Director of Medical Devices Morgridge Institute for Research Madison WI

2 Conflict of Interest Statement Board of Directors of Novelos Corp Board of Directors of Compact Particle Accelerator Corporation Board of Directors of HealthMyne I also own shares in these companies.

3 Outline The Infinitron Reaching perfection in cyclotron and synchrotron design Fixed-Field Alternating Gradient (FFAG) Cyclinac Dielectric Wall Acclerator (DWA) Laser Plasma Accelerator Funding to bring these technologies to life

4 The Infinitron Schultz and Kagan (Med. Phys. (30) 273, 2003) postulated the Infinitron as the hypothetical ultimate radiotherapy device. The Infinitron would deliver the desired dose to the tumor and give zero dose to normal tissue. IMRT with IGRT is closer to the Infinitron than conventional photon therapy IMPT is closer than IMRT

5 Dose Contrast Resolution Apply Boost or Avoidance (Negative Boost) Dose to Regions of Varying Size CTV R P r 1 r 2 R B r 6 r 3 Boost (GTV) or Avoidance Region r 4 R T r 5 Normal Tissue From Ryan Flynn, University of Iowa

6 Step and Shoot Tomo Intensity Modulated Protons

7 It is crazy medicine and unsustainable policy. Proton radiotherapy will fail if it cannot be made much less expensive.

8 Nearly at End of Development of Cyclotrons and Classical Synchrotrons Superconducting cyclotrons are in proton radiotherapy with fields that would be difficult to surpass Classical synchrotrons have been reduced in size, complexity and cost Improvements going forward will be modest.

9 Superconducting Cyclotrons Varian From Varian Mevion (>9 tesla) From Eric Klein, Wash U) Difficult to increase the magnetic field strength further

10 Classical Synchrotrons ProTom Small Beam Pipe Small Magnetic Volume Small Magnets

11 Evolution of the Fixed-Field Alternating Gradient (FFAG) Accelerator Simultaneously invented by Tihiro Ohkawa in Japan, Keith Symon at the UW-Madison and Andrei Kolomensky in the USSR in 1950 s. The most intensive early studies were carried out by Symon, Donald Kerst and others at the UW-Madison MeV/nucleon Ion FFAG < 3 m PAC Particle Accelerator Corp EMMA, Daresbury Laboratory, U.K. World s first ns-ffag Adapted from Carol Johnson, FermiLab < 5 m PAC ns-ffag design is a compact accelerator producing variable energy ~DC beam up to 330-MeV for proton and 430 MeV/nucleon for ion therapy

12 FFAG: Hybrid of a Synchrotron and Cyclotron Looks like a Synchrotron Strong Focussing ( Alternating Gradient ) Dipole field increases with particle energy Unlike Synchrotron: fields are constant in time ( Fixed Field ) and vary wth position: increases across beampipe Orbit changes marginally with energy Adapted From Roger Barlow, Huddersfield University, UK

13 The Non-Scaling FFAG F=focusing, D=Defocusing Scaling FFAG have a constant orbit shape and nonscaling FFAG do not Abandon scaling principle lose control of tune and fall into resonance? If the tune changes rapidly, resonances don t have time to destroy the beam. Rapid acceleration: Big turn-to-turn variation in energy Adapted From Roger Barlow, Huddersfield University, UK and Michael Craddock, TRIUMF, UBC

14 Accelerator Frontiers High Energy Machine Particle Energy Vs. Beam Power Particle energy is converted to create new particles. Trend Favors Linear Accelerator Linear collider machine because synchrotron radiation at bending magnet is too wasteful. E.g., International Linear Collider Synchrotron Light Source Particle energy is converted to photon. Linear machine because small emittence cannot be preserved for many turns. E.g., European Free Electron Laser High Power Beam Beam power is converted to produce secondary beams. Linear machine because it is believed to be easier to handle beam loss. E.g., European Spallation Source Adapted from Shinji Machida, CERN Accelerator School

15 Cyclinacs = Cyclotron (60 MeV) Linac (Variable 60 to 200 MeV) U Amaldi, Nuclear Instruments and Methods in Physics Research A 521 (2004)

16 Dielectric Wall Accelerator HGI Blumlein Laser Optical coupling Proton source Focusing HGI Beam SiC photoconductive switches Monitor Stack of Blumleins

17 Dielectric Wall Accelerator Timing System Thousands of Photoconductive Switches Source HGI Laser

18 Prototype DWA System Courtesy Compact Particle Accelerator Corporation

19 Prototype DWA System 20 MV/m has been achieved for system High gradient insulator >50 MV/m Switch reliability has not been proven at high gradients Viable clinically at 35 MV/m Courtesy Compact Particle Accelerator Corporation

20 Laser Proton Accelerator Titanium Hydride Foil High Atomic Number Foil

21 Laser Proton Accelerator >10 17 W in s High Power Light is Absorbed by the Foil Creating a Plasma

22 Laser Proton Accelerator Electrons Escape Leaving Heavy Positive Plasma

23 Laser Proton Accelerator Titanium Hydride Plasma Is Created

24 Laser Proton Accelerator Lighter Protons are Driven from the Heavier Ions

25 Laser Proton Accelerator Lighter Protons are Driven from the Heavier Ions

26 Laser Fast Ions Blow Off Plasma Electron Cloud Target

27 Laser Proton Gantry Systems Ma et al, Laser Physics 2006; 16:1-8

28 Laser Proton Gantry Systems Ma et al, Laser Physics 2006; 16:1-8

29 Temporal Structure Continuous Beam? Energy Electronically Adjusted? Time to Vary Emax Cyclotron Yes No >50 ms Synchrotro No Yes 1 s n Cyclinac Yes Yes 1 ms DWA and Laser Accel No Yes At pulse period FFAG Nearly Yes ms

30 Cost to Research and Develop New Proton Technologies ns-ffag $hundreds of millions $30-60 million more Dielectric Wall Accelerator $36 million already $30-70 million more Plasma Laser Accelerators ~$50 million already $ million

31 Conclusions Cyclotrons and synchrotron development has matured FFAG technology, having a combination of cyclotron and synchrotron characteristics, looks promising Cyclinac is a cyclotron married to a linac The DWA is a light weight, compact, high gradient inductive accelerator The laser plasma accelerator may be the most compact if emittance can be lowered