Squeezing the proton towards small proton therapy systems
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Squeezing the proton
towards small proton therapy systems
Roelf Slopsema. M.Sc. / UF Health Proton Therapy Institute
Disclosures • I worked as an R&D physicist for IBA from 2002 until 2004 • I have received a research grant from IBA in 2007 • I have performed paid consultancy work for MevIon in 2013 • I work at a center that has IBA equipment • I like protons • I am not a PhD
Learning objectives
After this presentation you…….
• …. know what proton therapy is
• …. have an overview of the historical development of proton
accelerators and proton therapy
• .... have an understanding of the different factors driving the
development of smaller PT systems
• …. know the different technologies applied to make PT
systems smaller
• …. have an idea of the small proton therapy systems available
now, in the near future, and in the distant future
Overview
• what is proton therapy?
• technical challenges of proton therapy systems
• history of proton accelerators and PT systems
• rationale for smaller PT systems
• technology for smaller PT systems
o limited-angle gantry
o superconducting cyclotrons
o linear accelerators
o laser-accelerated protons
• current status and outlook for the future
What is proton therapy? (1)
• Proton therapy (PT) = type of radiotherapy that uses high-
energy protons to irradiate diseased tissue
• The process through which high-energy protons loose energy
while traversing matter results in a distinct depth dose
distribution called the Bragg peak
• The penetration depth of the Bragg peak can controlled with
the entrance energy, allowing for complete sparing of
structures distal to the target
PT depth dose distribution
PT delivery techniques
Several different delivery techniques are applied in PT:
• 3D conformal proton therapy : using a block (aperture) and
range compensator to conform the dose to the target
– passive scattering
– uniform scanning
• Spot scanning : using many, scanned, small beams of varying
energy to ‘paint in the target’ (allows for IMPT)
PT dose distribution
3D conformal XT IMRT 3D conformal PT
http://www.cancernetwork.com/articles/improving-therapeutic-ratio-hodgkin-lymphoma-through-use-proton-therapy/page/0/2
PT dose distribution
Technical challenges of PT delivery (1)
Energy loss in coulomb interactions with shell electrons for electrons1 or protons2:
Ek : kinetic energy 46 MeV/cm
E0: rest energy
electrons: E0 = 0.511 MeV
protons: E0 = 938.3 MeV
2.1 MeV/cm
2.0 MeV/cm
10 MeV electrons: =0.93 → 1/2=1.2
10 MeV protons: =0.14 → 1/2= 51
1700 MeV protons: =0.93 → 1/2= 1.2
At same kinetic energy protons lose much more energy than electrons because of higher mass.
1: Moeller cross section ; 2 Bethe equation (http://pdg.lbl.gov/2014/reviews/rpp2014-rev-passage-particles-matter.pdf)Technical challenges of PT delivery (2)
Range: dE/dx ↑ → RCSDA↓
You need large proton energy to get sufficient range in the body.
2.5 cm (EYE) : Ek ≥55 MeV
16 cm (BRAIN): Ek ≥160 MeV
32 cm (ABDOMEN): Ek ≥230 MeV
Note: Compared to electrons,
protons scatter little allowing
deep penetration with little
lateral deflection around the
initial beam direction.Technical challenges of PT delivery (3)
Magnetic rigidity of a charged particle –
charge 1, rest energy E0, kinetic energy Ek:
High E0 and Ek results in high BR
For example,
bending a 250 MeV proton with a 1.5 T field
results in a bending radius of 1.6 m,
requiring a 2.5 m long magnetic field for a 90◦ bendTechnical challenges of PT delivery (4)
1. You need high proton energy to achieve
sufficient range inside the patient
→ large accelerator
2. The high proton kinetic and rest energy results
in large magnetic rigidity
→ large bending radii / large magnets
3. Clinical applications require beam delivery from
different angles with respect to patient
→ large gantry structuresInvention of the cyclotron
• invented in 1931 by
Lawrence & Livingstone
• Noble prize in 1939
• 4.5 inch, 80 keV
4.5-inch cyclotron Ernest Lawrence1931 / 11 inch cyclotron / protons to 1 MeV
1937 / 37 inch cyclotron / deutrons to 8 MeV
"He creates and destroys."
1939 / 60 inch cyclotron / deutrons to 16 MeV "I must confess that one reason we have undertaken this biological work is that we thereby have been able to get financial support for all of the work in the laboratory. As you know, it is much easier to get funds for medical research." —Lawrence to Niels Bohr, 1935
Atomic explosion over Hiroshima.
1946 / 184 inch synchrocyclotron / protons to 340 MeV
Evolution of accelerator energy
Birth of proton therapy
Robert Wilson: “Higher-energy machines are now under construction, however, and the
ions from them will in general be energetic enough to have a range in tissue comparable to
body dimensions. It must have occurred to many people that the particles themselves now
become of considerable therapeutic interest.”
‘Radiological Use of Fast Protons’,
http://users.physics.harvard.edu/~wilson/cyclotron/bobwilsn.html R.R. Wilson, Radiology 47(1946), 487-491Birth of proton therapy
• 1954 first patient treated
with protons at Berkeley
Radiation Laboratory
• irradiation to destroy the
pituitary gland in patients
with hormone-sensitive
metastatic breast cancer
Robert Stone and John Lawrence, Ernest's
brother, treat a patient with neutrons from
the 60-inch cyclotron.Development of proton therapy
• 1957 : results from Berkeley duplicated in Uppsala, Sweden
• 1961: Harvard Cyclotron facility starts PT
• 1990: first hospital-based PT system opens at Loma Linda
University, CA
• 2001 : PT starts at MGH
• 2006-2014: an additional 10 large, hospital-based PT centers are
opened in the U.S. (I.U., M.D. Anderson, UF, Upenn, Hampton Uni., …)
• 2013 onwards: introduction of smaller, one-room PT systemsIBA cyclotron: 230 MeV, 220 tons
IBA gantry: 38 feet tall by 35 feet wide, >200,000 pounds
Five-room proton therapy center as installed at Scripps (San Diego, CA) http://www.varian.com/us/oncology/proton/technology.html / http://www.scripps.org/services/cancer-care__proton-therapy
Rationale for smaller systems
Rationale for smaller systems
High cost of PT equipment limits widespread adaptation of
proton therapy.
Linear accelerator: $2.8 million (2.4-3.0) 1
5-room PT system: $144 million 2
1 Modern Healthcare / ECRI Institute Technology Price Index July 2013 (http://www.modernhealthcare.com/article/20130724/NEWS/307249943)
2 http://www.proton-therapy.org/zapper.htmRationale for smaller systems
‘smaller systems’ can reduce cost by…..
• reducing foot print of building
• eliminating need for construction of dedicated
building/room
• reduction in #components
• making PT available for smaller centers (one
room) or as extra modality in existing centers
(economy of scale)
• make proton therapy more compatible with
conventional forms of RTTechnical challenges of PT delivery (4)
1. You need high proton energy to achieve
sufficient range inside the patient
→ large accelerator
2. The high proton kinetic and rest energy results
in large magnetic rigidity
→ large bending radii / large magnets
3. Clinical applications require beam delivery from
different angles with respect to patient
→ large gantry structuresApproaches to smaller PT systems 1. Limit the number of treatment rooms 2. Reduce the foot print of the building (land/shielding) • accelerator under gantry • accelerator on gantry • reduce required shielding (proton absorption / degradation) 3. Shrink the size of the accelerator • superconducting cyclotron • linear accelerator with very high potential gradient • laser-accelerated protons 4. Shrink the size of gantry structure / beamline • short gantries • limited-angle gantries / fixed beam line
Limit the number of treatment rooms
IBA Proteus system with four rooms
IBA Proteus system with one room
Take a multi-room facility and strip away
all tx rooms except one....
→ smaller, but not very cost effectiveReducing foot print - cyclo under room
Sumitomo PT system:
• single gantry
• double-decker
• small vault foot print:
16mx20m
http://lightions.com/news/sumitomo-proton-therapy-system-clears-fda-510k/16Shrink size gantry – Sumitomo short gantry http://www.aapm.org/meetings/2013AM/documents/Sumitomo.pdf
Shrink size gantry – few fixed angles
IBA – inclined beam line:
• two fixed beam lines (90 and
30deg)
• limited-angle gantry that
rotates just nozzle (not beam
line)
• robotic positioner
• often in centers with
additional ‘full gantry rooms’
http://www.aapm.org/meetings/2013AM/documents/Sumitomo.pdfShrink size gantry – limited angle
MevIon S250: 180 degrees IBA Proteus One : 220 degrees
http://www.aapm.org/meetings/2013AM/documents/Sumitomo.pdfReducing foot print – shrinking beamline
IBA Proteus One:
• incorporate energy-selection system into gantry
• move scanning magnets from nozzle to gantry
• conventional to superconducting cyclotron
• limited-angle gantry
scanning magnets
energy-selection system
degrader
http://www.aapm.org/meetings/2013AM/documents/Sumitomo.pdfReducing foot print – IBA Proteus One http://www.aapm.org/meetings/2013AM/documents/IBA.pdf
Shrink size accelerator – superconducting cyclo
First some cyclo basics….
Revolution period:
T = 2πm/B
But for relativistic energies:
m = γm0 → T increases with energy
To compensate for mass increase with radius you need to either….
• decrease RF frequency with radius > synchrocyclotron
• increase magnetic field with radius > isochronous cyclotronShrink size accelerator – superconducting cyclo
…some more cyclo basics….
Isochronous cyclotron
• continuous beam (~100 MHz)
• increasing magnetic field causes
vertical defocusing > need for complex
magnet shape
Synchrocyclotron IBA C230 isochronous cyclotron
• pulsed beam structure (kHz region)
• lower RF power
• simpler magnet design (weak focusing)
• earliest cyclotrons used for PT were synchrocyclotrons
• later commercial cyclotrons are isochronousShrink size accelerator – superconducting cyclo • superconductivity allows increase of magnetic field above levels obtainable with conventional electromagnets (several T) • higher magnetic field results in smaller bending radius (at same energy) r = mv/B • But, increased magnetic field makes vertical focusing difficult saturated poles > limit on field gradient between hills/valleys limit in spiral design • To account for this you either… stay with an isochronous cyclotron, but limit the magnetic field increase use a synchrocyclotron design allowing for higher magnetic fields
Shrink size accelerator – superconducting cyclo Varian MevIon TriNiobium Core IBA S2C2 SC isochronous cyclotron SC synchrocyclotron SC synchrocyclotron http://www.aapm.org/meetings/2013AM/documents/Sumitomo.pdf
Shrink size accelerator – superconducting cyclo
Comparison of normal and superconducting cyclotrons used for proton therapy
Manufact. Model Super- Type Energy Weight Diam. Peak B
conducting [MeV] [tons] [m] [T]
IBA C230 NO isochronous 230 220 4.3 2.2
Varian YES isochronous 250 90 3.1Reducing foot print - cyclo on gantry
MevIon S250 systemShrink size accelerator – proton linacs Issues with proton linear accelerators…. • long or high field gradients needed • protons move at relatively low speed (up to of 60% of speed of light) > large variation in speed along accelerator Potential benefits…. • variable energy without degrader (neutrons, shielding) • fast energy change • light: no need for (heavy) magnets in accelerator Different approaches…. • long cavity-coupled linac • dielectric wall accelerator
Proton Linacs - LIGHT
• LIGHT = Linac Image Guided Hadron Technology
• Spin-off from LHC project (R&D facility at CERN)
• LIGHT components:
– Radio-frequency quadrupole ‘injector’ (4.5 MeV)
– Side-couple drift tube linac (35 MeV)
– Cavity-Coupled linacs (10 accelerators > 230 MeV)
• Potential benefits1
– lower shielding requirements (no absorbers for energy modulation)
– fast energy changes (2-3 ms)
– (modular)
– (more compact)
– (lower cost) ‘We estimate that the cost of a LIGHT facility will be in the region of US$40m vs. US$160-200m for
those using cyclotrons or synchrotrons’
http://www.advancedoncotherapy.com/Our-LIGHT-system/Product-overviewLinear accelerators- LIGHT
Proton Linacs – Dielectric wall accelerator Principles of dielectric wall accelerator… • developed at Lawrence Livermore National Laboratory • uses fast switched high voltage transmission lines to generate pulsed electric fields on the inside of a high gradient insulating (HGI) acceleration tube • high electric field gradients are achieved by the use of alternating dielectric insulators and conductors and short pulse times • use of laser-controlled switching to ‘fire’ acceleration in phase with proton propagation and energy • DWAs are expected to reach acceleration gradients around 100 MV/m STATUS OF THE DIELECTRIC WALL ACCELERATOR, G. Caporaso et al, Proceedings of PAC09, Vancouver, BC, Canada
Proton Linacs – Dielectric wall accelerator AAPM presentation, R. Mackie, ‘Dielectric wall accelerator and distal edge tracking proton therapy system’
Proton Linacs – Dielectric wall accelerator AAPM presentation, R. Mackie, ‘Dielectric wall accelerator and distal edge tracking proton therapy system’
Proton Linacs – TomoTherapy PT system
• proton arc therapy
• using ‘distal edge tracking’Proton Linacs – CPAC system
CPAC = Compact Particle Acceleration Corporation
using dielectric wall technology
http://www.cpac.pro/index.htm / http://www.gizmodo.com.au/2012/03/the-petite-particle-accelerator-a-proton-gun-for-killing-tumours/mlShrink accelerator – laser-accelerated protons
Principles of laser accelerated protons…
• Target Normal Sheath Acceleration (TNSA)
• ultra-intense laser pulse hits thin foil >10 W/cm
19 2
• plasma plume created in focal region
• laser accelerates plasma electrons
• electrons exit on other side creating strong electric field TV/m
• protons (ion) are pulled out and accelerated under the
influence of created electric fieldShrink accelerator – laser-accelerated protons
Shrink accelerator – laser-accelerated protons
Characteristics current experimental systems…
• maximum proton energy of 70 MeV for a 100 TeraWatt laser
• development of PetaWatt lasers underway enough for clinical PT energies
• high power requires pulsed lasers
• 10 Hz repetition for ultra-short pulses (50 fs)
• few pulses per minute for long pulses (700 fs)
• biology experiments have been performed
Proton Accelerators, M. Schippers, in Proton Therapy Physics, Ed. H. Paganetti, 2012 / A compact solution for ion beam therapy with laser accelerated protons, U. Masood et al, Appl. Phys. B (2014) 117:41-52Shrink accelerator – laser-accelerated protons
Benefits of laser-accelerated protons….
• no need for accelerator
• no/less need of particle transport (mirrors
instead of magnets)
Challenges of laser-accelerated protons….
• laser power and maximum energy
→ need 1022 W/cm2 to get 200 MeV protons
• energy spread → loss of bragg peak
• ultra-short pulsed beam → extreme
instantaneous dose rates 1010 Gy/s (biology/dosimetry)
Proton Accelerators, M. Schippers, in Proton Therapy Physics, Ed. H. Paganetti, 2012 / A compact solution for ion beam therapy with laser accelerated protons, U. Masood et al, Appl. Phys. B (2014) 117:41-52PT system with laser-accelerated protons ‘Our proposed design for laser-driven beams results in a substantial reduction in size by a factor of 2-3, and hence weight, compared to the most compact conventional Ion Beam Therapy gantry systems….’ A compact solution for ion beam therapy with laser accelerated protons, U. Masood et al, Appl. Phys. B (2014) 117:41-52
Current status and outlook
• Currently most PT centers are large, multi-room facilities
• Recently the first one-room systems have started operation and
several more are under constructionOperational
Research-facility PT systems 12
http://www.ptcog.ch/index.php/facilities-in-operationOperational
Multi-room hospital-based systems
(IBA Proteus , Varian ProBeam, Hitachi ProBeat)
27
http://www.ptcog.ch/index.php/facilities-in-operationOperational
Multi-functional one-room systems
(MevIon S250, Proteus One)
2
http://www.ptcog.ch/index.php/facilities-in-operationUnder construction / Planned
0
Research-facility based systems 14
Multi-room hospital-based systems (Proteus, Varian , Hitachi ProBeat)
One-room systems (MevIon S250, Proteus One, single gantry) 13
http://www.ptcog.ch/index.php/facilities-under-constructionCurrent status and outlook
• Currently most PT centers are large, multi-room facilities
• Recently the first one-room systems have started operation and
several more are under construction
• Several new technologies (laser-accelerated protons, LINACS) are
interesting, but are likely not ready for clinical application in the
next 5-10 years
• How much these new technologies will reduce the cost of PT
systems, remains to be seen
• The continued growth of proton therapy will depend on both….
– the results of the effort of cost reduction and
– the clinical outcome of PT
– ‘politics’You never know, the next break through in proton delivery might be just
around the corner……
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