Advantages and challenges of SC magnets in gantries Alexander Gerbershagen röntgenstraling tumor Diepte in weefsel cm Dosis Unnecessary dose Xrays tumour Depth in tissue cm ID: 917038
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Slide1
23 August 2017
Paul Scherrer Institute
Advantages and challenges of SC magnets in gantries
Alexander Gerbershagen
Slide2röntgenstraling
tumor
Diepte in weefsel (cm)
Dosis
Unnecessary dose
X-rays
tumour
Depth in tissue (cm)
Dose
Particle therapy
23-Aug-17
A. Gerbershagen, Beam optics for proton therapy
2
Slide3Particle therapy gantries
23-Aug-17
A. Gerbershagen, Beam optics for proton therapy
3
Si
ze
: up to 13 m x 25 m
Weight: up to 600 t
Cost: ~ 10’s MCHF
Slide4Motivation: reduce facility’s CostWeightFootprintHeight
Use of
superconductivity:Potential to fulfill the criteria, Advantages result from the strong fields (e.g. high momentum acceptance),Additional costs from cooling,Additional risks from
quenching
,
Challenges
dealing
with
stray
fields.
Superconductivity in particle therapy
23 August 2017
4
Slide5Consider changing customer composition Research
centers …
… give way to large hospitals.
Major
interest
in treating the maximal number of
patients
Require
High reliability
of the machines
Maximal treatment interruption of couple of days
No quenching / good quench protection
/ fast recovery
Easiness
of
service
Minimal warm up and
cool down times
Particle therapy customers23 August 2017
5
Slide6Advantages of SC magnets in gantries Proton gantries
Carbon ion
gantriesReduction of: Reduction of:- power consumption - power consumption- weight => cost - weight => cost - sizeExample: ProNova SC360, 25t Example: Toshiba-gantry at NIRS, 300t
r
= 5.45, l =13 m (compare to
HIT:
r= 6.5 m, l= 25 m)
250
MeV p:
B
= 2.4
Tm 450
MeV/
nucl
C
6+
:
B = 6.8 Tm
=> Most distances dictated => Large share of distances dictated by by the purpose of the gantry:
the beam bending radiusd from final bend to the patientScanning system
Beam focussingDispersion suppression
23 August 2017
6
Slide7Strong electromagnetic fields in the magnetNeed high mechanical stability to counteract the effects of FLorentz
Strong
and extended stray fields Effect of iron in the surroundings B must be < 0.5 mT at the iso-center
=>
Require
passive/
active
shielding
Beam
scattering in
magnet
=>
Possible quenching?
Maintenance
Requires dedicated
know-howChallenges of SC magnets in gantries
23 August 2017
7
Slide8Energy modulation - ramping
Scanning is performed in layers
The energy change between two layers should be ideally performed in <100 ms The momentum step between two layers is ~1%
=> Two options:
Magnet ramping speed of ~1
%
dB/B in 100
ms
Gantry
momentum
acceptance
very large (Δp/p > 10-20%)
23 August 2017
8
Spread-out Bragg peak
tumor
Slide9Cooling of the SC magnetsTemperature variation due to magnet rampingAll
energy
stored in the magnet is transformed into thermal energyAC losses from Hysteresis in the superconductor
magnetization
Coupling
currents among the
filaments and
strands
Cooling options
Bath cooling
l
iquid helium (<4.5 K)
challenging to manufacture a rotating
cryostat
helium
quench pipelines have to be implemented
Forced flow cooling
supercritical helium at 4.5-5 K and 3-8
barrequires a cooling and pressurizing system
vibration in case of turbulent flowCryo-coolers directly coupled to the cold
massno cryogenic fluid in the magnetheat
removal is limited (~1.5 W at 4.2 K)loud
noise
23 August 2017
9
Slide10NbTiMost commonly used, >50 years
of
experienceDuctile materialVery thin filaments (<1 μm diameter) => reduce AC losses Nb3SnT
c
of 18 K
10x
price
of
NbTi
Brittle
, strain sensitive
MgB2
Tc of 39
K Low IC
even at low B
Low strain
tolerance
YBa2Cu307-x
Tc
of 92 K In form of a
tape on a carrier material
Available superconducting materials 23 August 2017
10
Slide11Existing SC gantries – Toshiba and NIRS
Carbon gantry
Significant size reduction: r = 5.45, l =13 m compare to HIT in Heidelberg: r= 6.5 m, l= 25 mUpstream scanning
Final
bend
: 4
magnets
with
different
aperture
23 August 2017
11
Slide12SC gantry design – Cockcroft Institute 330 MeV proton beam required for pCT10
identical superconducting magnets
Size comparable with existing nc gantries23 August 201712
Slide13SC gantry design – ProNovaProNova Gantry design
Two
achromatic sc bends,
each
with
2
dipoles
and
3
quadrupoles
between
them.
PSI design of
350 MeV gantry
was based on
this layout
23 August 201713
y-plane
x-plane
14 m
5 cm
5 cm
IN-Beam (2
)
: x = y = 3.0 mm , x’ = y’ = 7.0 mr
δ = 0%
δ = 3%
d_isoc
SCAN
y-plane
x-plane
14 m
5 cm
5 cm
SC sections
Input beam: x = y = 5.0 mm , x’ = y’ = 2.4
mrad
δ = 0%
Slide14Fixed-Field Alternating Gradient (FFAG)Cells consist of focusing, defocusing and focusing quadrupoles.
Orbit offsets for the required energy range are relatively small
=> very large Δp/p (>50%) for a fixed magnetic field => potentially allows treatment without change of B23 August 201714
Slide1523 August 201715SC gantry design – PSI & LBNL
Combined function magnets, e.g.
CCT
magnets
with alternating gradient
3-5
racetrack
magnets
Momentum
acceptance of
±12.5%
No energy selection needed
Degrader can be mounted on the gantry
Treatment
of
small
tumors without
SC field change
(~ 50 % of cases)
Treatment of large tumors with only one or two of such
changesCan be used i.e. for volumetric
rescanning on a very fast time scale
Normal
conducting
or
permanent
dipole
Degrader
and
collimators
Superconducting
achromatic
bending
section
Scanning
magnets
(
either
upstream
or
downstream
of
sc
bend
)
Iso-center
Slide16Summary23 August 201716
The weight and, for the heavy ions, the size advantage of
SC gantries promises significant cost and footprint
reduction
=> particularly
important
for
the commercial particle therapy
Some
challenges
remain
Fast
ramping of the magnetic
field,
Limited options for cooling and SC material choice, Patient located near the strong magnetic fields,
Need to keep high reliability and availability.
Use of SC magnets gains popularity and promises to give a
big push in development regarding
Cost efficiency,Practicality of such facilities,
Better accuracy via
new treatment and diagnostic techniques.
Slide1723 August 2017
23. August 2017
PSI,
Thank
you
very
much
for
your
attention
!
17