Thomas Rockwell Mackie
Emeritus ProfessorUniversity of Wisconsin
Director of Medical DevicesMorgridge Institute for Research
Madison WI
Unconventional Acceleration Systems for Proton Radiotherapy
• 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.
Conflict of InterestStatement
• 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
Outline
• 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
The “Infinitron”
Apply Boost or Avoidance (Negative Boost) Dose to Regions of Varying Size
RT
RP
r6
r5r4
r3
r2
r1RB
Normal Tissue
CTV
Boost (GTV) or Avoidance Region
From Ryan Flynn, University of Iowa
Dose Contrast Resolution
Step andShoot
Tomo
IntensityModulated
Protons
“It is crazy medicine and unsustainable policy.”
Proton radiotherapy will fail if it cannot be made much less expensive.
• 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.
Nearly at End of Development of Cyclotrons and Classical
Synchrotrons
Superconducting Cyclotrons
Varian Mevion (>9 tesla)
From Eric Klein, Wash U)From Varian
Difficult to increase the magnetic field strength further
Classical Synchrotrons
ProTom
Small Beam Pipe Small Magnetic Volume Small Magnets
EMMA, Daresbury Laboratory, U.K.
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
Evolution of the Fixed-Field Alternating Gradient (FFAG) Accelerator
70 - 430 MeV/nucleon Ion FFAG
PAC
< 3
m
< 5 m
Particle Accelerator Corp
Adapted from Carol Johnson, FermiLab
World’s first ns-FFAG
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.
Unlike Synchrotron: fields are constant in time (‘Fixed Field’) and vary wth position: increases across beampipe
Orbit changes marginally with energy
Looks like a Synchrotron
Strong Focussing (‘Alternating Gradient’)
Dipole field increases with particle energy
Adapted From Roger Barlow, Huddersfield University, UK
FFAG: Hybrid of a Synchrotron and Cyclotron
The Non-Scaling FFAG
• “Scaling” FFAG have a constant orbit shape and non-scaling 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
F=focusing, D=Defocusing
Accelerator FrontiersParticle Energy Vs. Beam Power
Trend Favors Linear Accelerator
High Energy Machine
Particle energy is converted to create new particles.
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 formany turns. E.g., European Free Electron Laser
High Power Beam
Beam power is converted to produce secondarybeams.
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
Cyclinacs = Cyclotron (60 MeV) + Linac (Variable 60 to 200 MeV)
U Amaldi, Nuclear Instruments and Methods in Physics Research A 521 (2004) 512–529
Optical coupling
Proton source HGI
Stack of “Blumleins”
SiC photoconductive
switchesMonitor
Focusing
Laser
“Blumlein”HGI
Beam
Dielectric Wall Accelerator
Laser
Source
Thousands of Photoconductive Switches
Dielectric Wall Accelerator
Timing System
HGI
Prototype DWA System
Courtesy Compact Particle Accelerator Corporation
PrototypeDWA
System
Courtesy Compact Particle Accelerator Corporation
• 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
Laser Proton Accelerator
High Atomic Number Foil
Titanium Hydride Foil
High Power Light is Absorbed by the Foil Creating a Plasma
Laser Proton Accelerator>1017 W in 10-15 s
++++++++++++
Electrons Escape Leaving Heavy Positive Plasma
Laser Proton Accelerator
++++++++++++
Titanium Hydride Plasma Is Created
+++++++
+++++++
Laser Proton Accelerator
++++++++++++
Lighter Protons are Driven from the Heavier Ions
+++++++
+++++++
Laser Proton Accelerator
++++++++++++
+++++++
+++++++
Lighter Protons are Driven from the Heavier Ions
Laser Proton Accelerator
Laser
Blow OffPlasma
Target
Electron Cloud
FastIons
Laser Proton Gantry Systems
Ma et al, Laser Physics 2006; 16:1-8
Ma et al, Laser Physics 2006; 16:1-8
Laser Proton Gantry Systems
Temporal StructureContinuous Beam?
Energy ElectronicallyAdjusted?
Time to Vary Emax
Cyclotron Yes No >50 ms
Synchrotron
No Yes 1 s
Cyclinac Yes Yes 1 ms
DWA and Laser Accel
No Yes At pulse period
FFAG Nearly Yes 10-20 ms
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 + $150-200 million
• 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
Conclusions
