overview of presentation impt 2.protons vs...

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PAUL SCHERRER INSTITUT

Tony Lomax, Mayneord-Phillips Summer School, July 2009

Tony Lomax Centre for Proton Radiotherapy, Paul Scherrer Institute, Switzerland and

Department of Physics, ETH (Swiss Institute of Technology), Zurich

Proton (and light ion) therapy

9 field IMRT planProtons



Overview of presentation

1. Passive scattering, discrete scanning and IMPT

2. Protons vs photons

3. Clinical results from PSI

4. Summary



Why protons?

R.R. Wilson, Radiology 47(1946), 487-491



The Bragg peakE.g. Depth-dose curve for 177 MeV protons

0 5 10 15 20 250

1

2

3

Depth in water (cm)

Dos

e pe

r pr

oton

(nG

y)

Dose plateau where velocity is high

Dose peak where protons slow down

and stop

Width of peak dependent on

range straggling in medium and initial energy spectrum

Peak-to-plateau ratio 4-5

(depending on width of energy

spectrum)

Dose concentrated in small volume in Bragg peak.

2c)(

1

β∝

dR

dE



A mono-energetic proton Bragg peak is not very useful for treating anything other than the smallest tumours.

The problem of lateral field size and coverage in depth

To make protons useful , we need to spread out the dose laterally and along the beam direction.

Target volume

FWHM~9-11mm

σ~5-8mm

σ~3-5mm



Extending the dose in depthThe ‘Spread-Out-Bragg-Peak’

target

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Extending the dose in depth

The range shifter wheelA rotating wheel with

varying thicknessThe range shifter wheel in action…

RS wheel rotates continuously in beam at ~3000 rpm



Range-shifter wheel Scatterer

Collimator

Compensator

Target

Patient

Passive scattering in practice

Field specific aperture (collimator) matching projected

shape of target

The collimator

2D Projection of target along beam direction

• Each delivered field (incident direction of irradiation) requires specific collimator and compensator

• As range shifter is up-stream of scatterer(s), extent of SOBP is fixed across field



Passive scattering in practice

Computer-milled compensators

(examples from Orsay)

Example collimator

Eye irradiation

Generally, a compensator and collimator are required for every field in the passive scattering approach



Passive scattering in practiceSingle passively scattered

field

10cm

Fixed extent SOBP leads to poor sparing of normal tissue proximal to target

Three passively scattered fields

Conformation of dose can be improved through the use of multiple fields



Target

Magnetic scanner

‘Range shifter’ plate

Patient

Proton pencil beam

Discrete scanningPAUL SCHERRER INSTITUT


Spot definition

Incident fieldIncident field

Spot selection

Spot weightoptimisation

Optimiseddose

Dose Calculation

Discrete scanning – a treatment planning example

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Note, each individual field is homogenous across the target volume

F1 F2

F3 F4

Combined distribution

Discrete scanning: Single Field, Uniform Dose (SFUD) mode



1 field

Discrete scanning

1 field

Passive scattering

3 fields 3 fields

Passive scattering and discrete scanning compared



The simultaneous optimisation of all Bragg peaks from all incident beams.

F1 F2

F3 F4

Combined distribution

Lomax, Phys. Med. Biol. 44:185-205, 1999

Discrete scanning: Intensity Modulated Proton Therapy (IMPT) mode



1 field

3 fields

IMPTPassive scattering

1 field

3 fields

1 field

SFUD

3 fields

The three ‘orders’ of proton therapy compared



Example clinical IMPT plans delivered at PSI

Skull-base chordoma

4 fields

3 field IMPT plan to an 8 year old boy

3 fields



Sources of protons for therapy

Cyclotrons

Relatively compact +

Continuous wave +

Fixed energy -

Higher amount of -contamination

Synchrotrons

Somewhat larger -

Pulsed -

Variable energy +

Less contamination +

Accel/Varian 250Mev

Cyclotron

3.5m Diameter

Loma Linda 250Mev

Synchrotron

6m Diameter

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3.5m diameter

PSI gantry 1

7m diameter

PSI gantry 2

12m diameter

Loma Linda

15m diameter

Heidelberg

Proton treatment gantries are (and

will remain?) large…

Treatment gantries for proton therapyPAUL SCHERRER INSTITUT






4. Summary



Single posterior 160MeV proton field,

80cm long

No patching of divergent fields

required

Irradiation time ~ 10-15 minutes

No comparison necessary…!

1. Medulloblastoma (5 year old boy)PAUL SCHERRER INSTITUT


Delivered single field plan 9 field IMRT plan9 field IMRT – second try

Factor 6 lower integral dose for protons

2. Desmoid tumor (12 year old boy)



4. Complex head and neck (IMPT vs Tomotherapy)

Tomotherapy 3 field IMPT

Widesott et al, IJROBP 2008




Tomotherapy 3 field IMPT


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Tomotherapy IMPT Ratio (Tomo/IMPT)

Contralateral parotid 1 21.7% 4.8% 4.52

Ipsilateral parotid 1 41.5% 14.3% 2.9

Larynx 2 1.4% 1.9% 0.73


NTCP averaged over all cases


1 End point – flow rate <25% after 1 year

2 End point - >= grade 2 enema after 15 months



Anaesthesia equipment is mounted on the patient

table and monitored by video during the

treatment

A close collaboration between PSI

(PD Dr Beate Timmermann) and

KiSpi, Zurich (PD Dr Markus Weiss)

5. Pediatric cases (protons/IMPT vs IMXT)




Work of Erik van der Boom

Average fields used:Protons: 1.9X-rays: 7.2

9 patients treated with protons at PSI compared to IMXT plans calculated retrospectively



Serial organ

Serial organ

Serial organParallel organ Parallel organ

Parallel organ

Average EUD (overlapping) Average EUD (<25mm)

Average EUD (>25mm)


Critical organ EUD’s as function of distance from PTV




Non-target tissue integral dose

Average reduction in integral dose - 2.03 (1.5-2.7)







4. Summary

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P04109 P04088

Prescription dose:

74 CGE

37x 2 CGE fractions

Brainstem surface 63CGE

Brainstem centre 54CGE

Optical structures 60CGE

1. Skull base chordomas and chondrosarcomasPAUL SCHERRER INSTITUT


Local control probability (n=42 Chordoma, n=22 Chondrosarcoma)

1. Skull base chordomas and chondrosarcomas

Ares et al, submitted to IJROBP 2008



1. Skull base chordomas and chondrosarcomas

Publication n Radiation Mean dose 5 year PFS

Debus et al 2000 37 Photons (stereotactic) 66.6 50

Cho et al 2008 19 Photons/ Gammaknife 60.0 40

Munzenrider and Liebsch 1999 169 Photons+

protons 72 64

Hug et al 1999 33 Photons+ protons 71 59

Noel et al 2005 100 Photons+ protons 67 54

Ares et al 2008 42 Active scanning protons 73.5 81

Gay et al 1995 46 Surgery NA 65



P07155P04070

2. Extracranial chordomas and chondrosarcomas

Prescription dose:

74 CGE

37x 2 CGE fractions

Spinal cord surface 60CGE

Spinal cord centre 54CGE



Months

0

.2

.4

.6

.8

1

0 10 20 30 40 50 60

Without implant(n = 13)

Implants (n =13)

3-yr, 5-yr 100%

3-yr 69%5-yr 46%

Rutz et al, IJROBP, 67 (2007) 512-20

Local control rate

2. Extracranial chordomas and chondrosarcomasPAUL SCHERRER INSTITUT


Publication Indication n Median dose Local control

Weber et al (2007) Adult Sarcomas 13 69.4 74% (4 yrs)

Rutz et al (2008)

Pediatric and adolescent Chordoma/

Chondrosarcomas

10 74(66) 100% (36 months)

Timmermann et al (2007) Pediatric patients 16 50 75%

(1.5 yrs)

3. Other indications from PSI…

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Summary

• Proton therapy is a mature technique, with more than 50,000 patients treated world wide

• Spot scanning/IMPT provides improved flexibility and conformality in comparison to passive scattering

• IMPT is being delivered routinely at PSI with about 40% of all patients receiving IMPT as part of their therapy

• Initial clinical results with scanning are very favourable, and most new proton facilities will include scanning component

•Proton therapy is experiencing a ‘boom’ period in Japan, US and (continental!) Europe



P+

Thanks for your attention…

Why proton therapy in Switzerland?



Gay et al 65% PFS at 5 years46 chordoma patients

67% (n=31) had total or near-total surgical resection

33% (n=15) had partial or sub-total resection

Ares et al 81% PFS at 5 years42 chordoma patients

0% (n=0) had total or near-total surgical resection

100% (n=42) had partial or sub-total resection

Gay et al: “Radiotherapy with high-energy particles, or by focussed radiation, is recommended if the tumour cannot be totally removed”

The ‘Brada’ argument

‘Proton therapy is no more effective than surgery…’

overview of presentation impt 2.protons vs...

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