Talk outline
Tradition of radiotherapy @ PSI
Some remarks on scanning techniques
The Proton Beam Therapy Facility at PSI
Motivation for, and brief description of, PROSCAN project
- description of the COMET cyclotron
T. Garvey and J.M. Schippers,
Paul Scherrer Institut
New treatment gantry and scanning improvements
Conclusions
Villigen, Switzerland.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California), 27thJuly, 2009.
Why use protons for radiotherapy?
Radiation dose should be delivered to
tumour while sparing the healthy
cells that surround the tumour. The
existence of the Bragg “peak”
makes protons an attractive choice for
therapy.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Generic proton therapy facility components
accelerator
energy selection
beam transport
PSI
gantry
Spread-out Bragg peak
Control system:
- accelerator + beam transport
- treatment delivery + verification
- Interlocks + safety systems
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
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Parasitic use of research facility for patient treatment.
Classical “scattered” proton beam delivery technique
Passive scattering –
essentially for eye treatments.
Ring cyclotron
590 MeV, 2 mA
Energy
modulator
Injector I cyclotron eye treatment (1984)
> 5000 patients treated
at OPTIS-1.
Shaped
collimator bolus
Scatter foils
Gantry 1
(1996)
~ 400 patients
treated.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Spot scanning technique developed at PSI
Better for larger, deep seated tumours. Allows a “pencil” proton beam to deliver
a high dose with high precision for a precisely specified period of time.
Spot scanning: step & shoot
Results in better dose distribution.
Beam size 7 mm FWHM
5 mm steps
Compact “Gantry-1” at PSI (1996)
Lucite
plates
set
depth
scanning proton
pencil beam
10‘000 spots/liter (21 x 21 x 21)
Dose painted only once
~1 Gy /litre/minute
Table motion
Transverse motions via fast scanning magnet and patient table movement.
Depth variation by range shifter (lucite plates) in front of patient.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Eros Pedroni
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
2
Gantry 1 – in use at PSI for treatment since 1996.
Most compact of all existing
gantry designs, φ ~ 4 m
Limitations of spot-scanning technique with Gantry 1
• Beam spreading due to multiple scattering in the lucite plates.
- less sharply demarcated dose distributions
• Relatively slow motion of table movement
• Dynamic treatment suffers from tumour or organ movement during scan
- under/over dosage may occur
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Motivation for the construction of the PROSCAN Facility
•Difficulties of parasitic use of Ring Cyclotron in a multi-user research environment
• Ring cyclotron and spallation neutron targets require long maintenance shutdowns
~ 4 months per year during which no treatment is available.
• Further development of PSI spot-scanning technology
• Fast scanning techniques to deal with organ motion
• Transfer of technology to industry and radiation therapy centers
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
The PROSCAN facility consists of;
A 250 MeV proton cyclotron – COMET (COmpact MEdical Therapy cyclotron)
An energy “degrader”
Beam lines equipped with diagnostics
Therapy equipment
previously existing gantry 1
new gantry
new eye treatment facility – OPTIS-2
experimental beam line.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
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Characteristics of the COMET cyclotron
Cyclotron (1930)
Ernest Lawrence
Magnet
(1901-1958)
pole
coil
oscillating high voltage
on “Dee” electrode
Ion source
Vdee~
Energy gain
E=Vdee
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
The 250 MeV Cyclotron
Based on a design from
NSCL (H. Blosser).
Delivered by
ACCEL/Varian.
RF System
Frequency
RF power
Dee voltage
72.8 MHz (h = 2)
100 kW
80 – 130 kV
Beam properties
RF-Electrodes: 2 “Dees”
At each electrode border:
COMET is a compact 4-sector AVF isochronous cyclotron employing
a superconducting magnet.
Extractor:
-HV
Energy
Extracted current (max.)
Extraction efficiency
Vert. emittance
Horiz. emittance
Momentum spread
# of turns
250 MeV
800 nA
80%*
< 3 mm-mrad
< 5 mm-mrad
± 0.2%
* Important for activation
650
issues.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Main components of cyclotron
Iron yoke: shapes
field
Proton source
Strong ACCEL/PSI
Collaboration.
Ordered – April 2001
First extracted beam –
April 2005
Beam to gantry – June 2006
First patient – February
2007.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Coils (super
conducting)
RF: accelerates
protons
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
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Internal proton source
Internal proton source
cathode at -HV
anode
pole
Chimney
with
slit
~5 cm
pole
-80 kV
+
Dee 1
- - - Vertical
+ + + deflection plates
anode
cathode at -HV
pole
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Intensity control
Max. intensity set by:
proton source
pole
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Central region
Vertical deflection plate:
- Beam on/off
- Intensity modulation
-V
+V
Deflector plate:
sets requested intensity
- within 50 %s
- 5% accuracy
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
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RF-System
Image of lower “Dee’s”
+
+
-
Liner
( )
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
+
-
+
4x “Dee”: ~100 kV
72 MHz
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Extraction from COMET
Cryogenics: closed He-system 4x1.5 W
80%
Electrostatic
extraction
elements
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Low activation
24 h after beam off (extracted beam integral: 200 µA.h)
on pole:
400 - 500 µSv/h
mid plane:
250 - 400 µSv/h
10 cm unshielded degr.
500-1000 µSv/h
next to shielded degrader
10-20 µSv/h
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
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Beam-energy adjustment
Degrader for fast beam energy change.
Main disadvantage of cyclotron is its “fixed” energy.
“Degrader” is used to alter energy of beam delivered to patient.
Degrader unit
Cyclotron
Quad. triplet
Steere
r
Variable thickness of material is inserted in front of beam to vary
energy from 70 to 238 MeV.
5 mm range variation produced in 50 ms.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Kicker
dispersive focus;
position E-error
Carbon wedge degrader
238-70 MeV
5 mm ∆Range
in 50 ms
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Availability 2008 (first 9 months)
Collimating apertures define acceptance of beam transport system and
limit emittance of degraded and “scattered” beam.
Translatable carbon wedge degrader
Collimator for emittance limitation
3516 hours
puller
puller
95%
Cavity
Dipole magnet and energy selection slits limit E/E to ± 0.7%
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
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Fast pencil beam scanning & IMRT
The problem in dynamical treatments:
Organ movement
Cont. scanning “TV” mode
After each layer:
Energy change in 80 ms
Danger of
underdose and/or
overdose
- Multiple scans of tumor
- increase scan speed
- intensity modulation
intensity
kHz-Intensity modulation
PROSCAN approach:
0
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
10
7 s for a 1 liter volume.
Target repainting:
15-30 scans / 2 min.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
3D Pencil beam scanning
E=155
=>
rgy ne) E=150 MeV
e
n la
ne np
V
oto (sca E=145 Me
r
P h
t
p
de
time (ms)
New Gantry 2 at PSI (2009)
MeV
scanning magnets (x & y)
for 2D // scanning
No patient specific
R=components
in nozzle
3.5 m
~180 t
L=12 m
an
sc
ts
e
am
gn
be
Ma
ci l
n
pe
Eros Pedroni
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
8
Gantry - 2
Gantry-1 connection: check point
Beam verification by user:
Measurements at Check point
Connection to Gantry-1
Intensity
monitor
collimator
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
Profile monitor
Halo monitor
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
DIAGNOSTICS
cyclotron
radial probe
phase probe
+SE M
1-500 nA
+SE M
m aterial
irradiation
OPTIS2
<10 nA
~2 nA
range
shifter
CP
kicker
individual collim ator
m odulator
scatter foils
range shifter
degrader
~0.4 nA
range
shifter
(single)
Gantry 2
CP
M achine C ontrol S yst.
set-up:
centering, energy ...
continuous:
Gantry 1
current, centering, loss -->
CP
~0.4 nA
inser-/fixed ionization chamber
table
m onitors
current
profile
position
halo
loss
range
shifter
direct/without current m easurem ent
m ulti-leaf Faraday cups
Faraday cups/stoppers
slits
collim ators
dipoles/steerer/quadrupoles
can enforce stability
and reproducibility
U ser C ontrol S ystem
current -->
dosim etry
Pa tient S afety S ystem
current, position,
transm ission, dosimetry
(+ non diagnostics) -->
safety
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
9
Conclusions
• The long tradition of radiotherapy at PSI is
strengthened by the PROSCAN project.
• The choice of a superconducting cyclotron as a dedicated
accelerator has proven to be judicious.
• COMET is performing in a satisfactory and reliable fashion
• The installation of such a facility in a hospital environment
could be envisaged.
Acknowledgement: I should like to thank the PSI communications department,
and my colleagues, H. Fitze, R. Dölling, J. Düppich, S. Forss and R. Köferli for providing
Images. The PROSCAN project is the result of the work of many people at PSI.
Thank you for your attention!
T. Garvey, 51st Annual Meeting of the American Association of Physicists in Medicine, Anaheim (California) 25th July, 2009.
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