Recent developments in cyclotrons for proton therapy at...
Transcript of Recent developments in cyclotrons for proton therapy at...
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We Protect, Enhance and Save Lives.
Recent developments in
cyclotrons for proton therapy at
IBA
Yves Jongen.
Founder & CRO
IBA sa
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06A typical PT center €30-55 millions for equipment
€45-100 millions for the center€€3030--55 millions for equipment55 millions for equipment€€4545--100 millions for the center100 millions for the center
80-100 m
35 m
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The accelerator is a very small part of a PT system
� A Proton therapy system is much more than an accelerator
� It is most often a complex, multi-room system, filling a Hospital building.
� The treatment rooms are larger than the cyclotron vault
� The total investment is around 100 M€, of which 45 M€ for the equipment
� The cyclotron represents only 7 M€ of this!� The investment to develop the cyclotron was less
than 4 M€, out of more than 60 M€ spent on developing IBA PT system
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06Proton Therapy end of 2007
PT center under operation
Courtesy Janet Sisterson & PTCOG
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NCC, Kashiwa
MGH, Boston
MPRI, Indiana
UFPTI, Jacksonville, FL
Beijing, China
NCC, Ilsan
WPE, Essen
13 IBA PT customers in the world
Orsay (France)
ProCure 2 Chicago
Hampton Univ., Virginia
Wanjie, China
U.Penn, Philadelphia
ProCure 1Oklahoma City
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06IBA has currently the largest installed base in PT
PT Installed base shares - PROTON -(1994-2008) in ROOMS
IBA60%Hitachi
13%
MHI13%
Varian7%
SHI3%
Still River4%
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06Cyclotrons for Proton therapy?
� In 1991, when IBA entered in PT, the consensus was that the best accelerator for PT was a synchrotron
� IBA introduced a very effective cyclotron design, and today the majority of PT centers use the cyclotron technology (not only IBA but Varian, Still Rivers)
� Over these 15 years, users came to appreciate the advantages of cyclotrons:�Simplicity�Reliability� Lower cost and size�But, most importantly, the ability to modulate rapidly
and accurately the proton beam current
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06Proton beam current regulation
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06Change of energy?
� Cyclotrons are simpler at fixed energy� Energy change by graphite/beryllium degrader at
waist after cyclotron exit, followed by divergence slits and energy analyzer
� This very effectively decouples the accelerator from the patient
� Unlike the synchrotron, the emittance is identical in X and Y. This makes gantry optics much easier in scanning mode
� Yes, neutrons are produced, but ESS is well shielded and the average beam current in PT is low > limited activation
� How fast? 5 mm step in energy in 100 msec at PSI (vs. 2 sec for IBA or 4 sec. for a synchrotron).
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06The IBA ESS
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06More ExpertiseThe energy selection system
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06More ExperienceUFPTI, Jacksonville, USA
• Construction start date: Mar 2004• PT equipment installation start: Mar 2005• 1st Patient : Aug 2006 ! • today : 130 patients/day treated in 3 Gantry rooms• up to 250 fields/day
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06The UPHS Particle Therapy Centre, Philadelphia
•The largest Particle Therapy centre to date!• 4 Gantry Rooms•1 Fixed Beam Room (2 beams) + 1 Experimental Room• Beam since July 2008• First patient treatment in Autumn 2009
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06Procure center #1, Oklahoma city, USA
• First center of the Procure network• 2 Gantry Rooms• 1 Fixed & Inclined Beam Room• Beam since July 2008• First patient treatment in Autumn 2009
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06Hampton University Proton Therapy Institute
• 4 Gantry Rooms• 1 Fixed Beam Room• All equipment installed• Beam accelerated in the cyclotron
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06Westdeutsche Protonentherapiezentrum, Essen
• First Particle Therapy centre based on a Public Pri vate Partnership (PPP) model•3 Gantry Treatment Rooms•1 Double Fixed Beam Room with Eye Treatment line• Beam since September 2008• First patient treatment in Autumn 2009
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06New cyclotron and gantry for CPO in Orsay
• New equipment for an existing PT center• New cyclotron, ESS and one new gantry room• Transition to be made without interrupting treatmen ts !!!!!• 2 existing Fixed Beam Rooms• All equipment installed, cyclotron beam extracted, optics tuning ongoing
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06C230 median plane view
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06C230 in numbers
� 230MeV, 500nA proton beam for therapy� Resistive but high field magnet: 2.9T peak field, 1.1m
extraction radius, 4 spiral poles, elliptical gap, 800A, 524 kA-turns, 9mm pole gap at outer radius
� Internal hot filament PIG source� RF system: 106MHz 100kW, harmonic mode 4, dee
voltage from 60 kV at the center to 120 kV at extraction
� Electrostatic deflector extraction
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06More ExpertiseThe CYCLONE 230 cyclotron
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06The cyclotron opens at median plane for service
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06Inside the cyclotron
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06The ion source and central region
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06Electrostatic deflector
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06Recent improvements on the C230
�15 C230 cyclotrons have been built, but we keep adding improvements. Recent developments include:�Correction of slight tilts in the orbit plane
�Design improvements in the RF cavities�New deflector design
�Improved beam current regulation
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06Recent improvements on the C230
�15 C230 cyclotrons have been built, but we keep adding improvements. Recent developments include:�Correction of slight tilts in the orbit plane
�Design improvements in the RF cavities�New deflector design
�Improved beam current regulation
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06RF cavity redesign
� Problem:Due to the elliptical pole shape, the counter-dee gap decreases with radius.
� Consequence:Beam losses on counter-dees at large radius.
� Solution: Maximize the counter-dee gap.
� Method:Redesign the RF cavities to increase the counter-dee gap from 10mm to 12mm.
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06RF cavity redesign
� New cavity design
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06RF cavity redesign
� New cavity design
Redesigned area
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06RF cavity redesign
� New cavity design
230MeV orbit
12mm
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06RF cavity tuning redesign
� Problem:The present cavity tuning by a variable capacitor in the median plane needs periodic replacement. It is difficult to share the larger RF current drawn by this capacitor equally in the upper and lower cavity.
� Consequence:Capacitor failures: loss of reliabilityLack of up-down symmetry: leaks of RF in the cyclotron through the accelerating gaps
� Solution: Tune the cavities with inductive tuners in the valleys sliding on RF contacts
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06New cavity tuner design
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06Electrostatic deflector optimization
� Problem:The ‘old’ septum intercepted a significant amount of beam.
� Consequence:Activation, limited extraction efficiency…
� Solution:Reduce septum beam apparent thickness.
� Method:Analytical study and beam tracking. Then build it and try it!
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06Electrostatic deflector optimization
� Beam tracking simulation of ‘new’ deflector.
Pole edge
Circulating beam
Extracted beam
Deflector
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06Electrostatic deflector optimization
� Beam tracking simulation at JINRComparison between ‘old’ and ‘new’ septum :
1%0%Losses inside deflector on HV plate
1%8%Losses inside deflector on septum
9%28%*Losses on septum entrance (0.1mm)
‘New’‘Old’
* plus circulating beam
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06Electrostatic deflector optimization
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06Experimental results
� Radial track using integral radial probe
Beam currenton externalbeam stop
(Raw data, not corrected for RF noise and radial probe efficiency.)
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06Experimental results
� Radial track using integral radial probe
Adj. dowel pinsNew RF cavity
Adj. dowel pinsNew RF cavityNew deflector
Integral radial probe beam current External beam stop current
Def
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06Proton beam current regulation optimization
� Present situationThe proton beam current is slaved to an external time function by measuring the extracted beam with an ion chamber, doing a digital regulation by varying the arc current in the ion source. The current loop regulates the beam current with an accuracy better than 2%, up to a bandwidth of 2.5 KHz
� Problem:We have a “dark current”. Even when the arc is turned off, a proton beam current of 30 to 100 picoampere is extracted from the cyclotron
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06Proton beam current regulation optimization
� Consequence:The dark current results in small inaccuracies in beam delivery. In pencil beam scanning, it can result in small amounts of beam being delivered outside the treatment field
� Solution:Use a reduction of the dee voltage to suppress the proton beam when it is not needed. Possibly, use the dee voltage variation exclusively to regulate the beam current
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063 kV dee voltage variation is enough
Beam current vs Dee Voltage
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06Modulating the dee voltage by 3 kV at 62 kHz!
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06Regulating 500 µsec pulses
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06Data analysis on IC cyclo, 4 nA peak
Regulation triangle 100 Hz 4 nA
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Thank you…