Cyclotrons for Therapeutic

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Cyclotrons for Therapeutic Medical Diagnostic
ApplicationsActivities in VECC
Malay K. Dey On behalf of Accelerator Physics
Group, VECC
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Plan of Talk

• 30 MeV Proton Medical Cyclotron

• Design Studies on

• 10 MeV PET Cyclotron with Permanent Magnet

• 250 MeV Superconducting Proton Cyclotron for
  Therapy

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30 MeV Proton Cyclotron

• PET and SPECT isotopes
• RD Experiments in Material Sciences
  radiochemistry

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Medical Cyclotron Magnet
Coils
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Ion Source and Injection Line
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Four Sectors
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Inflector and Central Region
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Two DeesCapacitive Coupling
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RF System
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Beam Diagnostics Pop up Probe
Located at about 10th turn (approx. 2 MeV)
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Extraction Port
Stripper Foil Drive
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Layout of Medical Cyclotron Facility
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MATERIALS SCIENCE BEAM LINE
Proton beam Energy 15-30 MeV, Beam Current
350?A Beam spot size at target location 10mm,
Scanning frequency 200 Hz / 20 Hz orthogonal,
Beam dimension at Target location 30 mm X 30 mm
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Beam Line for Target Studies
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Magnetic Field Measurement Setup
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Median Plane Magnetic Field Distribution
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Radial and Axial Focusing Frequencies
Tune Diagram and Resonances
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Energy Vs Radius
Isochronization Frequency Error
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Test Results
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PET Cyclotron (10 MeV) using Permanent Magnet
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Design Challenges

• Compact Magnet for 10 MeV proton energy
• Optimal choice of average magnetic field and
  pole size
• Minimum permanent magnet volume
• Enough focusing by Hill-Valley sectors
• Enough space in valleys to accommodate RF
  structure

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Specifications
PM
Iron
B Mag Flux density, H Field Strength V
Volume, R Pole radius, L Pole gap E
Energy of the particle
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NdFeB Magnetic Properties
Neodymium Iron Boron (NdFeB) demagnetization
curves
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Material fraction in the simulation ½ model
PM
Al
Iron
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Tosca Model
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1/8 th MODEL
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1/8 th MODEL
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PM Configuration
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Magnetic Field DistributionVertical Sectional
View
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Magnetic Field lines
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Median Plane Magnetic Field Distribution
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Smoothening the Field Data

• Interpolation
• Fourier Harmonic Analysis

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Hill Valley Field
5 cm 15 25 35
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Optimization of Field Profile
Average Field Distribution at different iterations
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Fourier Harmonic Components
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Optimization of Fourth Harmonic Component
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Effect on the Eighth Harmonic Component
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Radial and Axial Focusing Frequencies
at Different Iterations
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?r and ?z Vs Energy and Radius
Frequency error (?o /?)-1
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Static Equilibrium Orbit Properties
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Tune Diagram And Resonances
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Sumulation Of Dees with TOSCA
Fourth Harmonic Operation RF Frequency 82 MHz
Electric Potential Distribution
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Electric Field Lines at the Central Region of
Cyclotron
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Distribution of Electric Field
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Analysis of Accelerated Orbit Dynamics
in the Combined Magnetic and Electric Field

Electric Potential
Magnetic Field
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250 MeV SuperconductingProton Cyclotron for
Therapy
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Specification for Clinical Proton Beam

• Beam Range decides Energy of the Beam
• 250 MeV proton 38 gm/cm2 in
  water
• Energy accuracy 0.4 MeV
• Energy spread 0.1 MeV FWHM
• Beam Intensity is decided by Average Dose Rate
  
• Beam current 2 17 nA is
  sufficient
• Time Structure of the Extracted Beam
• Intensity fluctuation Tolerance
  50 within 50 µs
• Duty Factor gt 10
• Beam Abort Time 60 µs
• Quality Emittance 2-5 p mm-mrad,
  Positional Stability 1 mm,
• Angular stability 1 mrad
• This determines the over all accuracy reqired
  in designing the cyclotron magnet, RF and
  Extraction system

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Key Parameters of the Proton Cyclotron
to be optimized
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Design Challenges
MAGNET STRUCTURE

• In K500 SCC the acceleration of proton is
  prevented by
• Dangerous Resonances
• Insufficient focusing limit 160 MeV
• Max Electric Field in Deflector 140 kV/cm

RF SYSTEM

• K500 SCC RF system is complex
• Iindependently excited Dees, Large Range of
  frequency
• 250 MeV SCC RF system requires
• Fixed frequency and 4 dees,
• Ttwo opposite dees galvanically coupled, other
  two dees are 180 degree out of phase
• All dees driven by single amplifier

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Profile of Sectors, Coil and Yoke
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TOSCA MODEL
Upper half of the cyclotron magnet
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3D Magnetic Field Simulation
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Four Sector Design
To avoid N/2 stop band
Isochronism Focusing
?1(T/A)/931.5 K500 T/A 80 MeV, ?1.1 K250
T/A250 MeV, ?1.26 To avoid resonance near

• Single Turn Extraction
• Four Dee configuration gives large Energy gain
  per turn

• Fast crossing of next most severe resonance at
• Push-Pull mode of acceleration

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Field Shape Optimization

• Isochronism Focusing is optimized by
• Proper field gradient, flutter and spiralling
• Proper positioning of the superconducting coil,
  its cross section, Current
• Increasing angular span of Spiral sectors -
  angle as fifth order polynomial of radius,

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Field Shape Optimization

• Focusing is achieved by
• Azimuthal field variation
• Spiraling of the sectors

Bext30 kG, R_ext85 cm
R_yoke 1.5 meter
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Trmming the Field by Iron Rods
Trim rods are movable up and dwon through the
central line of the Hills By Adjusting the
vertical positions of trim rods final tuning to
isochronous profile is achieved The positions are
set by an optimization technique Differential
Evolution
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Equilibrium Orbit Properties
?r and ?z vs Energy and Radius
Frequency error (?/?)-1
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2nd Harmonic Operation
Push-Pull Mode
Four 38 degree Dees B D are galvanically
coupled A C are 180 degree out of phase w.r.t.
their neighbours All are driven by single RF
Amplifier. Dee voltage 80 kV Energy Gain 390
keV per turn Full energy at 640 Turns
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Ion Source and Central Region of Cyclotron

• Cold Cathode Internal PIG type ion source
• High Brightness more than 100 micro Amps
• Extraction voltage and Source slit geometry can
  control the Plasma boundary, in turn beam
  emmittance

• Important issues in central region
• Electric Focusing
• Phase selection
• Phase to radius correlation
• Single turn extraction is required for specified
  energy width
• Centering of the orbit important in the context
  of Walkinshaw Resonance
• Bunching in time at initial turns high energy
  resolution
• Energy resolution also depends on Stability of
  magnetic field and RF voltage
• Low loss at extraction element and hence low
  activation of cyclotron
• Phase selection is achieved by retractable slit
  3mm dia tungsten rods with 0.2 mm aperture,
  selected phase /- 3.5 RF degrees

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Electric Focusing
Electric Field Calculation with RELAX3D
Z vs turn number for central ray and two other
rays Upper Rays are given initial axial velocity
w.r.t. central ray Lower Rays are given initial
axial displacement w.r.t. central ray
Solid Ray left the ion source at RF phase of 210
degrees, where 270 degrees corresponds to Peak
voltage, dotted ray 220 degrees, dashed 200
degrees
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Extraction System

• Precessional Extraction
• 2 Electrostatic Deflector
• 6 Passive Magnetic Channels
• 1 Active Magnetic Channle in Yoke
• Difference from K500 system
• Position is fixed, since the cyclotron operated
  at one fixed excitation
• Compensating bars and Front porch shims
  compensates the effect of fringing field of
  magnetic channels on the inner orbits

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Single Turn Precessional Extraction
An orbit precession or off-centered ness is
induced at Nu_r1 resonance A small localized
field perturbation having azimuthal first
harmonic component is used to induce a coherent
precission of desired amplitude
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Walkinshaw Resonance

• Coupling Resonance
• Effect Convert radial amplitude of
  coherent/incoherent oscillation into vertical
  amplitude. Beam loss on liners
• Since Nu_r1 resonance sets large radial
  precission, so walkinshaw resonance is brought
  before this, to avoid beam loss.
• This adjustment is done by
• adjusting radial fall-off of field by shimming,
  hill-shoe etc
• adjusting spiral angle at extraction Nu_z can be
  increased/decreased
• Centering the orbits at central and acceleration
  region to keep radial oscillation amplitude small

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OUR VISION AND MISSION
TO APPLY THE TECHNOLOGY FOR THE BENEFIT OF MANKIND
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THANKS