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E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 1
CHIBA
1.5.2010
GANTRIES
Eros Pedroni
Paul Scherrer Institute
SWITZERLAND
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 2
1. GENERAL CONCEPTS - MOTIVATION
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 3
What is a proton (ion) gantry?
• A rotating beam porta rotating beam line(rotating accelerator?)
• For treating the patientin supine position
• With maximal flexibilityto apply the beamfrom any desireddirection
…just a rotating beam line?
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 4
Same purpose as in conventional therapy?
• Photon therapy requires multiple beam incidences (many fields)
– Needs “opposed” beam directions
to compensate for the exponential fall-off of photons in depth
in order to achieve a dose distribution sufficiently homogeneous
– A gantry is a “must”
• Charged particles can in principle deliver a conformal dose just from a single direction…
Small diameterof the gantry
Large air gapto the patient
Example of photon gantry: Clinac 2000
Gantry head can rotate below table between table and floor
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 5
PTIMRT
Courtesy of A. Lomax PSI
• Term of comparison
– Photon-IMRT
• Advantage of protons
– Reduction of the integral dose outside
of the target (no low dose “bath”)
Charged particle beams needs less beam directions
• Example of a single field which can compete well with IMRT
• But• Often a single field is not optimal
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 6
Major difference to photon therapy … the gantry size!
• Magnetic rigidity of proton beam requires big beam transport elements
– Proton beam – Bending radius > 1.5 m @ magnetic field 1.5T (near saturation of the iron)
– Almost not feasible to mount the accelerator directly on the gantry (quality losses)
– Not possible to rotate the gantry in the small space between patient table and floor
– A PT gantry (with beam from below) has to cope with a deep gantry pit
R=1.5m3 m9 m
Photons
Protons
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 7
Ion therapy gantries?
• Gantry for ions
– Magnetic rigidity is another factor of 3 higher as compared with protons
– Size of the gantry is doubled – weight and costs are correspondingly higher
• For ions: fixed beam lines are presently the standard solution
• Example of an ion facility The HIMAC facility
– Horizontal - vertical and
tilted beam lines
– The first dedicated ion
therapy facility in the
world
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 8
• Treating patient also in sitting position
– Eye treatments (no use of CT data required)
• Use of several fixed beam lines
– Horizontal beam line
– Horizontal and vertical beam line in the same room
– Or others … like 45° beam incidence
• Combined use of fixed ion-beam lines with proton gantries in the same facility Hyogo, Medaustron…
Alternatives of using a proton gantry ?…
From a flyer of Mitsubishi – Hyogo facility
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 9
• Use of a sophisticated patient table
– 6d-table to rotate the patient in 3d space
• Chair with vertical CT• Use of combined roboters holding each
the patient andthe imager (cone-down CT)
Alternatives of using a proton gantry ?…
Genesis Inc. Boston USA (80’s)
Schaer Engineering
Pavia facility
Siemens – Heidelberg facility
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 10
Reasons to use of a gantry with proton therapy?
• Beside the “obvious reasons” …
– Treat the patient in supine position
• In the same position as at the time of CT-data-taking for treatment planning
• To keep the position of internal organs unchanged (body soft tissues)
– For best comfort of the patient
– To apply several fields (“beam incidences”)
• To redistribute the plateau dose over several tissues
• To stay below the tolerance of organs at risk
…
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 11
… dose precision reasons…
• Select those beam directions which
– Avoid sensitive organs OAR
– Avoid density heterogeneities
in the patient body
• Dose errors due to
interplay of MCS and
range
• Shadows at density
interfaces parallel to the
beam (bones and metal
implants)
– Select beam directions
with low ranges
(keep the plateau dose short)
From Barbara Schaffner thesis
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 12
Main reason to use a gantry… IMPT !!!
• IMPT (intensity modulated therapy)– Simultaneous optimization of dose fields
– Superposition of non-homogenous dose fields
• Requires the use of a gantry– Need to apply all fields in the same session
• Requires scanning
Courtesy of
A. Lomax
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 13
• For protons: the use of a gantry is today the established standard solution
• Standard approach – one accelerator feeding many (identical) gantries
ExampleThe IBA facility at MGH in Boston
The “majority”solution for proton therapy
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 14
2. BRIEF HISTORY OF GANTRIES
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 15
1991 - Loma Linda University (California USA)
• The first hospital-based proton therapy facility in the world
– Operational since 1991
– Synchrotron based (Fermi-lab technology - Optivus)
– 3 gantries and two horizontal rooms
• Based on passive scattering
Milestone 1
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 16
Side view Front view
• The first proton gantry in the world
• “Cork screw” gantry
– Handy Kohler invention
(Harvard cyclotron)
– Radial extent on a disk
– Saving shielding (volume)
• Recently
– Replacement of the
patient table with a
robotic solution
Loma Linda
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 17
1992 the GANTRY 1 of PSI (Switzerland)
• The first scanning gantry of the world (1992)– (Human) patient treatments started in 1996
• Characteristics:– Upstream parallel scanning
– Gantry radius reduced to only 2m
– Eccentric mounting of the patient table on the
gantry front wheel
Milestone 2
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 18
X Sweeper magnet most often used
Y Range shifter 2nd loop
– Gaussian pencil beam of 3 mm sigma
– Cartesian scanning (infinite SSD)
– “Step and shoot” – spot delivery on a 5 mm grid
Z Patient table slowest loop
Time Spot dose: Monitor + Fast Kicker
The sequence of the elements of scanning:
Discrete pencil beam scanning
Scanning on the PSI Gantry 1
– Weak point:: transverse scanning by moving patient table
– Slow motion ( no repainting possible)
– We can treat only non moving targets
– Head, spinal chord and low pelvis
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 19
“Standard” commercial solutions – … end of 90s …
• Last bending magnet with 135°– Shortest path up-down - shortest length
– Cylindrical treatment cell – gantry pit
• Systems with passive scattering (later also scanning)
Kashiva – 1998
Tsukuba - 2001
Boston – 2001
Hyogo – 2001
….
R > 2m
Milestone 3Schär Engineering - Munich
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 20
• Very elegant solution to the gantry pit problem– Cylindrical treatment cell with rolling floors
• Flat in the middle with round walls
• Adapted to the nozzle rotation
• Supported with a counter-rotation at the interior of the gantry
Milestone 4
High-tech solution for the “gantry pit problem”
Example of a Sumitomo system Sumitomo patent
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 21
• At the new proton therapy facility in Houston
– M. D. Anderson Hospital (Texas)
– Delivered by Hitachi
• One of the 3 gantries is equipped with scanning
• Followed by RPTC Munichand MGH Boston
• The terms of competition remains beam size and scan speed
First commercial scanning gantry … in 2008
Milestone 5
RPTC Munich
The first fully
scanning-based facility
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 22
Nozzle options… effects on dose precision (beam size)
• Scattering nozzle– 1. scatterer
– Modulator
– 2. scatterer
– X-ray
– Jaws
– Monitors
– Snout
• Scattering and scanning combined– Added X scan magnet
– and Y scan magnet
• Scanning only– Only X scan
– and Y scan
• Scanning + simulated scattering
Vacuum window?
Vacuum window !
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 23
45° dipoles scannermagnets
treatment
room
absorber
First gantry for ion therapy – Heidelberg HIT
Milestone 6
90° dipole
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 24
3. WHAT TO CARE ABOUT GANTRY DESIGNPSI Gantry 2 as an example
Our main goal: maximize performance
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 25
Environment of the patient table
• Gantry rotation limited to -30°to + 180 ° (instead of 360°)• Flexibility of beam delivery by rotating the table in the horizontal plane
• Analogy with longitude and latitude in the world-geography
• Permanent fixed floor for a better
access to the patient table
• Fixed walls for mounting supervision
equipment - like Vision-RT
• Adaptive solution for using
newly developed diagnostics
equipment
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 26
In-room positioning with sliding-CT
• Within reach of the patient table
– Sliding CT of Siemens– Use of time-resolved images
before (and after) treatment
• Adapt dose field to the
organ situation of the day
(body regions with soft
tissues)
• Setup of respiration gating
• Other possibilities??
– CT-PET? MRI?
• Other options
– Cone down CT
– 2 fixed 45° X-ray
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 27
BEV X-ray - simultaneous to proton beam?
• Equivalent to portal imaging with KV photon• Large field-of-view area (26 cm x 16 cm) not masked by equipment• For QA control of gating and tracking (scanning + pulsed X-rays)
a) compact gantry b) long throw gantry
SweepersX rays tube
Proton beam
Bending
magnet
nozzle
Yoke hole
Patient
Imager
Sweeper
or
Scatterer
Collimator
On-line control of the
position of moving
targets during beam
delivery
Alternative - two
orthogonal
45° X ray tubes
Image Guided
Proton Therapy ?
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 28
• Vacuum “close to the patient”
– Sharp pencil beam - 3 mm sigma
• Monitors• Pre-absorber
– IN and OUT of beam (motorized)
– For ranges below 4 cm ?
• Telescopic motion of the nozzle
– To reduce air gap (keep patient at isocenter)
• Option to add collimator and compensator
– To shield OAR on top of scanning
• At low energy PTCOG poster Safai
– To simulate scattering ? PTCOG talk Zenklusen
• Collision protection remote control of patient table
– multiple fields in one go
Optimized nozzle design -> dose precision
Compact design
Successful testing of the
breaking the vacuum window
Acoustic shock within tolerance
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 29
Small size of pencil beam – for best lateral fall-off
• Beam size between 3 and 5 mm sigma at “all” energies
70 MeVσ = 0.5 mm
230 MeVσ = 0.25 mm
Continuous variable
energy from 70 MeV
to 230 MeV
Avoid air gap problem
(the distance nozzle to
patient
affecting the lateral
dose fall-off)
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 30
GANTRY 2 beam optics with parallel scanning
11.7m
3.2m0
7.9m
Q1 Q2
QC
Q3
Q4
Q5 Q6 Q7
A1
A2 A3
Sy
S1yH1
S2yS2xH2
K
T U
M1
M2
M3
P1
T
U
24° exit angle of the pole of the 90° bending magnet
Time reversed track calculation: parallel beam to focus in U and T
Place sweepers at U and T focus -> parallel scanning
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 31
Dynamic beam energy
• Continuous choice of the beam energy (70 MeV -230 MeV)– Setting all elements of the whole beam line within a single command
– Up-down down-up
• Shown
– 80 ms dead time for range steps of 5 mm
Gantry 2 beam seen with a big
scintillator block
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 32
Use of the variable modulation of the beam intensity
• Modulation of the beam intensity at the time scale of 100-200 µs
– Deflector plate and vertical collimators in the first beam turn after the ion source
– Time delay to extracted beam in the order of 100 µs– Manipulate beam before it is accelerated
• Examples
– “Pulsing beam”
– Painting of of a line segment with variable beam intensity
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 33
Flexible control system
• Steering file for combined delivery of
– Spots
• Spot scanning as the default (starting) mode
– Lines
• For maximum repainting number
– Contours?
• For optimizing repainting and lateral fall-off
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 34
Tabulated dose delivery using FPGAs
• Combined tabulated control of
– U-sweeper 0.5cm/ms
– T-sweeper 2 cm/ms
– Beam intensity
• As a function of time (10 us time scale)
Example 1 – Fast uniform scanning
(85 ms per layer) (6 x 8 cm)
494 energy layers less than 1 minute
Scanning can “simulate” scattering!
23 times
Max T speed
Variable intensity
10 cm in 5 ms
Example 2– Painting of dose shaped lines
For conformal scanning
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 35
Errors due to organ motion during scanning
• Disturbance of the lateral dose fall-off
– Same for scattering and scanning
• Add safety margins
• Reduce with Gating or Tracking
• Disturbance of the dose homogeneity
– Single scanning is very sensitive
– Remedies:
– Repainted scanning (Goal: 6-10s / liter / Gy)
• Alone – for medium uncontrolled motion
• With Gating or Tracking – for large motion
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 36
Milestone 7?
PSI Gantry 2
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 37
New ideas for ion therapy gantries?
• Superconducting magnets
– Could help in the future in realizing “small size” ion gantries (same size as proton gantry)
– Multiple complex coils - difficult to get good beam optics
– Rotating cryogenic system
– Slow energy changes
• FFAG lattice
– Permanent magnets
– Low weight gantry
– Static transport for variable energy
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 38
FFAG lattice - Trbojevic BNL
FFAG permanent magnets gantry
Workshop on Hadron Beam Therapy of Cancer, Erice 38
78o
r=2.71 m
h1=
1.5
8 m
13 cells - 25 cells
150o
h2=
2.4
2 m
Orbits magnified10 times
From a density of the No-Fe-B 11.7 gr/cm3
The weight of the whole gantry ~ 500 kg.
(Eberhard Keil)
h3=
4.2
9 m
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 39
Future “dream” solutions?
• Why not proton therapy like photon therapy?– From Photon-Tomotherapy to Proton-Tomotherapy ?
• Distal tracking? Rotational therapy with protons?
– (T.R. Mackie)
High gradient (100 MeV/m) Linac(dielectric wall)
Caporaso et al, Nucl Instr Meth B 261 (2007) 777
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 40
…or going for further simplifications?
• Still/River company (USA)– First beam announcement at
scientific meeting?
• Possibly a break through• Beam delivery method?
• ACCEL Varian– Compact synchrocyclotron on gantry
– With degrader and beam analysis section
• Very compact synchro-cyclotron– Single room solutions for small size hospitals
E. Pedroni Center for Proton Radiation Therapy - Paul Scherrer Institute - WE Chiba 01-05-2010 41
DEPTH
~ 20 cm-8 cm
8 cm
Lateralposition
PSI's major goal: advancement of pencil beam scanning
THANK YOU