aapm particle beam therapy symposiumaapm . particle beam therapy symposium . flanz 2013; aapm...

Particle Beam Technology and Delivery

AAPM Particle Beam Therapy Symposium

Flanz 2013; AAPM Symposium

Types of Accelerator Systems Cyclotron Synchrotron Laser Linac

FFAG

Isochronous Cyclotron

Synchro- Cyclotron

CycLinac Strong Focusing

Rapid Cycling

Weak Focusing

CycFFAG

DWA

Rf Linac

2 Flanz 2013; AAPM Symposium

Vladimir Derenchuk

Jay Flanz

Rock Mackie

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Particle Beam Technology & Delivery

Synchrotrons

J. Flanz, Ph.D. Massachusetts General Hospital

Harvard Medical School


Ongoing Themes in Field of Particle Therapy Examples for CONTEXT of Technology and Delivery:

1. Pencil Beam Scanning (PBS) – Impact on: Beam Parameters from Accelerator + Delivery – Scanning “type”; Beam Size; etc.

2. Image Guided Therapy (IGRT) – Impact on: Imaging; Beam Alignment – PROTON Radiography/Tomography ????

3. Organ Motion – Impact on: Beam Parameter timing; Beam Tracking

4. End of Range ® - Proton Range vs. HU ? 5. Field Directions(θ,ϕ,ψ): How to treat specific sites? 6. Lower Capital Costs $$$ 7. Increased Throughput

– Positioning, Aligning, Field-to-field time, Beam time

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These may not be new concepts, but they are the current foci owing to the fact that the ‘first’ round of system specs have been satisfied. (i.e. the Berkeley/MGH report of 20 years ago.)

X-ray Simulation Proton Radiography Simulation

Joao Seco, MGH


Separated Themes may not lead to system solutions! Need System Solutions

• How to deliver a Rx non-uniform dose distribution to a moving target with a desired conformance? vs. e.g. Continuous Beam Scanning: with 3mm Sigma – This involves beam parameter TIMING issues, beam trajectory

and range manipulation, Apertures (or not), etc. • How to deliver quality treatment to the appropriate number

of patients at an affordable cost? vs. e.g. Out of room setup; Energy Change in 2 seconds – This involves automated remote operations

• Imaging and Analysis and Correction of Position • Go from Field to Field without delays (e.g. Moving things remotely)

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It’s not just the accelerator. It’s the other components and how the accelerator works with the other components !


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Goal of Particle Radiotherapy • Deliver required dose to a target in a reasonable time • Deliver the correct dose distribution to the correct location

– Minimize the dose outside the target

A B

C

D E

Dosimetric Regions of Interest

Depth Direction

Transverse Direction

A B

C

D E

Dosimetric Regions of Interest

Depth Direction

Transverse Direction

• C&D = desired dose • A+B+E = unwanted dose

• E, B&part of A= desired dose • Some of A+(C-E) = unwanted

dose

E

(Scattering)


Use this as the building blocks to deliver dose

Spread out Transverse Dose with Scanned beam spots Y0

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Transverse spreading using superposition of unmodified beams.

Uniform dose scenario.

Gaussians are Magic

Spac

ing:

2 si

gma

1

sigm

a

Asymmetric Sharp Edged


Scanning – The “Penumbra” of a scanned beam

PSI/Berkeley

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Small beam sigma vs. Cut off edges.

In this case the Technology required has to deliver a dose modulated distribution

In this case the Technology required has to produce a different beam profile (where it counts).

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Materials in the Beam Path – Including the Patient

Stefan Schmidt

Ran

ge

Shift

er

4.5

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The Raw beam shape is NOT the only contributing factor

Dose / Dose Rate • Power = Joules/sec = Energy * Current

– e.g. 150 MeV * 1 nA = 0.15 Watts • Dose = Joules/kg ≡ Gray (Gy)

– Dose = (Power* seconds) /kg – e.g. 150 MeV * 1 nA * 60 sec = 9 Joules

• Water 1kg/1000cc = 1kg/liter • Dose = 9 Joules /1kg (in a liter) • 150 MeV, 1nA == 9 Gy in 1 liter in 1 minute • But not all energy goes into the target (see Bragg peak) 3-6

Gy in 1 liter in 1 minute

• Therefore, for 1Gy in 1 liter we need ~ 120 GigaProtons – (120 GP/min ~ 0.3nA)


What is a Synchrotron?

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Ener

gy

# Pr

oton

s

Time Flanz 2013; AAPM Symposium

Ring Orbit – Alternating Focusing

Unperturbed closed orbit

Perturbed a little - closed orbit

Perturbed a lot - closed orbit

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Focusing elements


Synchrotron Beam Dynamics


Resonant Extraction (one method)

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0

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Fiel

d St

reng

th

Horizontal Displacement

Linear

Octupole

• The process is partly stochastic (uncorrected time structure is not smooth)and • The extracted beam phase space is NOT Gaussian in the extraction plane (depending on the type of extraction). x

θ Extraction Septum


Beam size from the last magnet to Isocenter?

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ole

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er/W

eigh

t

1 sigma Isocenter Beam Size

Gantry Dipole Power / Weight

PS Current ~ Gap (2.1 sigma) Magnet weight ~ gap 2 Power ~ Current 2 ~ gap 2

Gantry/Beamline Dipole

Isocenter


Treatment Time Contributions Synchrotron

• Time to Inject • Time to Accelerate • Time needed to wait until the patient is

ready for particles (e.g. gating) • Time needed to extract particles

– Instrumentation will only allow a finite number of particles per unit time

• Time needed to Decelerate

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If m

ore

parti

cles

are

nee

ded

or c

hang

e en

ergy

Additional ‘cycle’ times are needed if there are not enough protons in the ring to deliver the required dose at a given range.


To

Tb

Breath

Variable Cycle Synchrotron Beam Available

Beam Available

Beam Available

Fixed Cycle Synchrotron or Cyclotron

CW Cyclotron

Okay to Deliver Beam

Time needed to wait until the patient is ready for particles

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Comparison of Beam Utilization for Treatment Requiring Synchronization

Effective Dose Rate may depend upon accelerator time structure


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Charges ⇒ repulsion Parallel currents ⇒ attractive

Are additional cycle times needed? Accelerator Physics: Space Charge effects

How many protons can be stuffed into a Ring?

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x

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Linear

Non-linear

Defocusing force

Gaussian density

distribution

y

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Coulomb


0.00E+00

2.00E+10

4.00E+10

6.00E+10

8.00E+10

1.00E+11

1.20E+11

1.40E+11

1.60E+11

0 2 4 6 8 10 12

Ext

ract

ed C

urre

nt (n

a)

Proton Injection Energy (MeV)

Proton Limit in Ring due to Space Charge Effects

Assumptions: A finite cycle time High Efficiency Extraction Beam Size

How many protons can be stuffed in a ring? How many are needed?

LLUMC MDA

Also 1Gy/min in a liter 113GigaProtons/min <3Gp/cycle

McLaren


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First Proton Therapy Synchrotrons

LLUMC, Tsukuba, MD Anderson, Shizuoka, Wakasa, HIMAC, Hyogo, McLaren, Mayo …

Hitachi Extraction


Rapid Cycling Medical Synchrotron the second generation

Synchrotron accelerator

Gantries

Synchrotron Extremes Faster/Bigger Smaller / Cheaper

• Current (~<nA?). • Beam Time Structure (maybe) - Scanning (not line?) / Organ Motion • Lower Emittance – Good for beamlines and Gantries • Energy Change time linked to acceleration time (Faster?) • At 30 Hz in 120 sec ==> 3600 pulses ! (What can be done ?)

• 10x10x10cm (@3mm spot) ~ 10,000 spots (ONE pulse/spot)

“Compact” Medical Synchrotron

Accelerator Physics VS. ANTI-Accelerator Physics?


NIRS Japan

Heavy Ion Accelerators and Facilities - Conventional

Remember: 400MeV/nucleon: Could be big and Expensive! But they are shrinking also !

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Heidleberg Flanz 2013; AAPM Symposium

What might someone do with a Blank Slate? • How to deliver a Rx non-uniform dose distribution to a moving

target with a desired conformance? – Scanning beams with adjustably sharp edges – Accelerator with timing consistent with Scanning and organ motion

(Flexible timing) – Appropriate on-line imaging

• How to deliver quality treatment to the appropriate number of patients at an affordable cost

– Accelerator Design: • Make it INEXPENSIVE, Simple

– Design only what’s needed » What Energy is needed? (Treatment, Tomography, … ) » What Current is needed? (Scattering, Scanning, Losses …)

• Simplify the Optics – Minimize Building costs; e.g. Some Shielding Requirements

• No ‘designed’ sources of BEAM LOSS – Chose a Beam delivery like Scanning


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Gratuitous Comments: • Treating with particles requires a system approach. • The various subsystems interact with each other and

depend upon each others capabilities. • Trade-offs include size, speed, intensity, of

everything, (equipment, beam etc.) • More and more demand for affordable particle

therapy solutions is apparent. • New Approaches are being fueled by both

accelerator interests, and by the more and more demanding requirements of particle therapy.

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The Francis H. Burr Proton Therapy Center

Thank You ! 25

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