Non-Scaling FFAG gantry for proton/carbon gantry
Dejan Trbojevic-BNL, Eberhard Keil-CERN, and Andrew Sessler-LBL
• Introduction
– Motivation for a new way of isocentric gantry design
• Carbon/proton gantries today–(Heidelberg, PSI, …)
• Spot scanning – alternative option
• The non-scaling FFAG gantries:
– Smaller proton gantry
– Carbon/proton gantry
• Engineering design – magnets are available
•
Summary
September 4, 2008
FFAG08 Manchester Workshop – Dejan Trbojevic
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MOTIVATION: large weight of the present gantries
• Large Br=6.76 Tm for carbon ions requires large magnetic fields.
• Presently the beam scanning requires very large magnet at the
end of the gantry to accommodate parallel beams to the
patient.
• Results are: very large magnets and large weight of the
transfer line and the whole support. The carbon/proton cancer
therapy facilities constraints are very difficult to fulfill with the
warm temperature magnets.
• This leads us to a new concept – non-scaling light small
superconducting gantry.
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Carbon Gantry in Heidelberg
Weight of the transport
components – 135 tons
Total weight = 630 tons
Length of the rotating
part =19 m
Carbon Ek=400 MeV/n
Br = 6.76 Tm
If: B=1.6 T then r ~ 4.2 m
If: B=3.2 T then r ~2.1 m
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Munich and PSI proton gantries
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Proton Gantry at PSI
1.27 m
7.4 m
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The proton gantry @ PSI
counterweight
110 tons
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Simulation Code: “SRNA” Vinca Institute @ Joanne Beebe-Wang
BNL
•
Monte Carlo code SRNA-2KG originally developed by R. D. Ilic [Inst. of Nucl. Science
Beograd, Yugoslavia, 2002] for proton transport, radiotherapy, and dosimetry.
•
Modified at BNL to include the production of positron emitter nuclei.
•
Proton energy range 0.1-250 MeV with pre-specified spectra are transported in a 3D
geometry through material zones confined by planes and second order surfaces.
•
Can treat proton transport in 279 different kinds of materials including elements of Z=198 and 181 compounds and mixtures.
•
Use multiple scattering theory and on a model for compound nucleus decay after proton
absorption in non-elastic nuclear interactions.
•
For each energy range, an average energy
loss is calculated with a fluctuation from
Vavilov’s distribution and with Schulek’s
correction. The deflection angle of protons
is sampled from Moliere’s distribution.
•
Benchmarked with GEANT-3 and PETRA.
A very good agreement was reached.
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Energy deposition of the 169 MeV protons
MeV-cm2/g
Adsorbed energy in
Within slices of Ds=1 cm
@ 12 cm
@ 11 cm
@ 10 cm
@ 9 cm
@12 cm
@ 8 cm
@ 7 cm
@ 6 cm
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@ 5 cm
@ 3 cm
@ 2 cm
FFAG08 Manchester Workshop – Dejan Trbojevic
@a 1 cm depth
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Vertical Profiles
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Experimental results from: NSRL Laboratory
at Brookhaven National Lab - Adam Rusek
Ion:
C6+
Peak position: 15.95 cm in high
density polyethylene (r=0.97 gr/cm3)
Kinetic Energy: 292.7 MeV/n
LET(in water): 12.9 KeV/mm
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Experimental results from: NSRL Laboratory
at Brookhaven National Lab - Adam Rusek
Ion:
H+
Peak position: 37.1 cm in high
density polyethylene (r=0.97 gr/cm3)
Kinetic Energy: 250.0 MeV/n
LET(in water): 0.392 KeV/mm
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Spot scanning technique – at PSI, Heidelberg, …
Problems with straggling and
multiple Coulomb scattering
require careful planning to achieve
1% accuracy in accumulated dose
Courtesy of Stephen G. Peggs
S. Peggs, "Fundamental Limits to Stereotactic Proton Therapy", IEEE
TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 51, NO. 3, JUNE 2004, 677
D. C. Williams, "The most likely path of an energetic charged particle
through a uniform medium", Phys. Med. Biol. 49 (2004) 2899–2911
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Straggling and multiple Coulomb scattering
Courtesy of Stephen G. Peggs
Mult. Coulomb
s
MS
~ 6.5 mm
Straggling
s
MS ~7.6
mm
The total beam size quadrature of the
multiple scattering beam size + optical beam size
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Skin depth and required number of voxels
Form factor f=1 for a perfect circle
D-entire depth of distance
total number of voxels require
number of pixels in each energy layer
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Skin Depth and required number of voxels
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Spot scanning preparation-longitudinal
Courtesy of Stephen G. Peggs
Varying the beam size during
therapy at different energies
and transverse positions.
q=32 mrad= tan-1(10 cm/3.2 m)
Adjusting btwiss
Beam direction
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“Parallel” and 30-40 mrad angle scanning
sT
Tumor
sOPT
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Transverse beam sizes
Normalized emittance e @ 0.5 p mm, kinetic energy Ek=200 MeV
sOPT= [(btwiss *e)/(6p bg)] g=1.138272/0.938272029=1.21316 bg=0.6868
btwiss(m)
sOPT(mm)
sMS(mm)
sT(mm)
qspread(mrad)
0.45
0.23
6.5
6.504
12.06
1
0.348
6.5
6.509
11.84
10
1.101
6.5
6.59
10.73
100
3.483
6.5
7.37
7.475
sT
qspread
sOPT
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Planning carefully the scan: find the right step size D
(start at the end ~10 cm)
#2
Central position
#1
D~3.14 mm
q2~30.3 mrad
~26 cm
Scanner magnet:
lsc=0.2m
Bscanner-max
=(q*Br)/lsc
Ek=250 MeV
Brmax =2.432 Tm
Bscanner-max = 0.38 T
q2=(0.10-D)/3.2m
12 mrad
Qmax~32 mrad
10 -D cm ~ 9.37 cm
~3.2 m
Towards the scanner
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~10 cm
qspread =12 mrad
D
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Example of the non-scaling FFAG carbon gantry-cell
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Proton Gantry with triplet and scanning magnets
(it could be built with small permanent magnets F=2 cm)
magnified +-10 cm
Magnet dimensions, magnetic fields and gradients:
L_BD = 25 cm, GD =-33.7 T/m, Bmax= 1.5 T + 33.7 T/m*0.012 mm = 1.9 T
L_BF = 30 cm, GF =+35.5T/m, Bmax=-0.25 T -+ 35.5 m*0.028 mm = 1.2 T
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Tracking of protons @ fixed magnetic
fields from 90 –250 MeV
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Towards smaller size-proton gantry with superconducting
magnets – height ~ 6 m
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Proton gantry with superconducting magnets
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Smaller non-scaling FFAG proton gantry – height 4.7 m
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Smaller non-scaling FFAG proton gantry tracking protons
with energies of 79-250 MeV @ fixed magnetic field
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Adjustment of the height with different number of cells
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PSI solution with the non-scaling FFAG
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Carbon gantry design
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Lattice functions
L= 22 cm
Very strong
focusing:
b x,y~1-2 m
Dmax~8.8 cm
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Simulation of the particle transport through the gantry
-5 mm
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+ 5mm
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Possible continuous coil magnet design for
the non-scaling FFAG gantry
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Magnets are available
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Combined Function magnet for the Carbon Gantry
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Summary
• Isocentric gantries are necessary in proton/carbon facilities but
presently made of too large and heavy magnets.
• Spot scanning is very essential for therapy. We presented a real
possibility of scanning at the end of the gantry.
• A new solution for the isocentric gantry design present reduction in
the gantry size and weight comes from the small superconducting
magnets – already available.
• The weight of 130 tons in the carbon isocentric gantry is reduced
to 1.5 tons.
• A follow up detail study of the spot scanning from the end of the
gantry will be presented soon.
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Experimental results from: NSRL Laboratory
at Brookhaven National Lab - Adam Rusek
Ion:
H+
Peak position: 26.1 cm in high
density polyethylene (r=0.97 gr/cm3)
Kinetic Energy: 205.0 MeV/n
LET(in water): 0.4457 KeV/mm
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Experimental results from: NSRL Laboratory
at Brookhaven National Lab - Adam Rusek
Ion:
C6+
Peak position: 8.375 cm in high
density polyethylene (r=0.97 gr/cm3)
Kinetic Energy: 200.2 MeV/n
LET(in water): 16.23 KeV/mm
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