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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


1. GENERAL CONCEPTS - MOTIVATION


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?


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


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


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


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


• 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


• 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


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

…


… 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


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


• 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


2. BRIEF HISTORY OF GANTRIES


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


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


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


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


“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


• 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


• 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


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 !


45° dipoles scannermagnets

treatment

room

absorber

First gantry for ion therapy – Heidelberg HIT

Milestone 6

90° dipole


3. WHAT TO CARE ABOUT GANTRY DESIGNPSI Gantry 2 as an example

Our main goal: maximize performance


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


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


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 ?


• 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


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)


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


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


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


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


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


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


Milestone 7?

PSI Gantry 2


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


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


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


…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


DEPTH

~ 20 cm-8 cm

8 cm

Lateralposition

PSI's major goal: advancement of pencil beam scanning

THANK YOU

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