proton therapy: past, present and future terapia con ... · proton therapy: past, present and...

Tony Lomax, La Fisica Medica in Lombardia, May 23rd 2007

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

Proton therapy: past, present and futureTerapia con protoni: Passato, presente e futuro

Spot scanning Passive scattering


Overview

1. The past: passive scattering

2. The present: spot scanning and IMPT

3. The future: dealing with uncertainties


Extending the dose in depth – the ‘Spread-out-Bragg-peak’

target

The past: passive scattering


Range-shifter wheel

Collimator Compensator

Target

Patient

Proton treatment delivery Making protons useful 1. Passive scattering in practice

Scatterer


Single 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



50 years of proton therapy.

Lawrence Berkeley Laboratory (USA) 1954-1992 >2500Los Alamos (USA) 1974-1982 >230Harvard/MGH (USA) >11000Loma Linda (USA) >10000Nice, Orsay (France) >5600Dubna, Moskau, St. Petersburg (Russia) >5200Chiba, Tsukuba, Hyogo, Kashiwa, Shizuoca (Japan) >4900PSI (Switzerland) >4400Clatterbridge (UK) >1300San Francisco, Bloomington (USA) >680Berlin since 1999, Catania (Sicily) since 2000 >680South Africa >470Uppsala (Sweden) >400GSI Darmstadt (Germany) >190Wanji (China) >30

Nearly 50,000 patients treated in 27 centres world-wide.



Overview



3. The future: dealing with uncertainties


Target

Magnetic scanner

‘Range shifter’ plate

Patient

Proton pencil beam

Spot scanning

Pedroni et al, Med Phys. 22:37-53, 1995

The present: spot scanning and IMPT


Making protons useful 2.Spot scanning in practice

Spot definition

Incident fieldIncident field

Spot selection

Selectedspots

Initial dosedistribution

Dose calculation

Spot weightoptimisation

Optimiseddose

Dose Calculation

Scheib, ETH Diss 10451, 1993



A spot scanned plan consists of the addition of one or more individually optimised fields.

Note, each individual field is homogenous across the target volume

F1 F2

F3 F4

Combined distribution



Intensity Modulated Proton Therapy: The simultaneous optimisation of all Bragg peaks from

all incident beams. E.g..

F1 F2

F3 F4

Combined distribution

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



1 field

3 fields

IMPTPassive scattering

1 field

3 fields

1 field

Spot scanning

3 fields

The three ‘orders’ of proton therapy comparedThe present: spot scanning and IMPT


0

10

20

30

40

50

60

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Year

Num

ber

of p

atie

nts

Between 1996 and end of 2005, 262 patients have been treated using scanned protons at PSI (+18 in 2007).



Case 1. A sarcoma in a 12 year old boy

Delivered single field plan 9 field IMRT plan

Factor 6 lower integral dose for protons



Patients treated at PSI since 1999

0

5

10

15

20

25

30

35

40

45

50

1999 2000 2001 2002 2003 2004

Year

Num

ber

of p

atie

nts

Patients with IMPT

All patients

Mean number of series (plans) per patient: 2.6

Mean number of IMPT series per (IMPT) patient: 1.3

Mean number of fields per IMPT plan: 3.3

Between 1999 and 2004, 43 of a total of 209 patients have been treated with IMPT as part of their full proton treatment.



Two examples of clinical IMPT plans delivered at PSI

3 fields

Sacral chordoma, 10 year old girl Skull-base chordoma

4 fields



Manufacturers currently offering photon therapy

equipment

Varian

Elekta

Siemens

Manufacturers currently offering particle therapy

equipment

Optivus (p)

Mitsubishi (p)

Ion Beam Applications (p,s)

Hitachi (p,s)

Varian/Accell (s)

Siemens (s)

Industrial suppliers of radiotherapy equipment



Overview



3. The future: dealing with uncertainties? (and the ‘Milano’ connection)


The advantage of protons is that they stop.

The future: dealing with uncertainties

The disadvantage of protons is that we don’t always know where…

10% range error


3 field IMPT plan to an 8 year old boy

Note, sparing of spinal cord in middle of PTV

Planning CT New CT

During treatment, 1.5kg weight gain was observed

Max range differences:SC 0.8cm

CTV 1.5cm


The ‘Milano’ connection:Alessandra Bolsi and Francesca Albertini


DVH

0%

20%

40%

60%

80%

100%

0% 20% 40% 60% 80% 100% 120%

Dose (%)

Vo

lum

e (%

)

nominal CTV

weight gain CTV

nominal CE

weight gain CE

Difference distribution

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Automatic adaptation of Bragg peak ranges on a spot by spot basis depending on local change in range




C T V

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100 110 120

D o se (%)

Vol

ume

(%)

N om ina l C TV

W eigh t inc reas e C TV

R ange adap ted C TV

N om ina l S C

W eigh t inc reas e S C

R ange adap ted S C




kV-CT

Accuracy of range calculation due to reconstruction artifacts?

MV-CT (tomotherapy)

No artifacts and linear relationship CT units to proton stopping power

Ospedale San Rafaele, MilanOspedale San Rafaele, Milan


The ‘Milano’ connection:Francesca Albertini and Ospedale San Rafaele


kV-CT

MV-CT

0

0.5

1

1.5

2

2.5

3

3.5

0 20 40 60 80 100 120 140 160 180 200 220 240

X (voxels)S

topp

ing

pow

er

KV SP

MV SP

ProsthesiskV-CT artifacts

Stopping power profiles

PTV

The ‘Milano’ connection:Francesca Albertini and Ospedale San Rafaele



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

• Protons are coming of age – many new facilities being built and planned, most will provide scanning capability

• However, protons bring their own challenges – e.g. detecting and dealing with range uncertainties

• We’re investigating this with the help of medical physicist trained in Lombardy…


P+

Grazie!

proton therapy: past, present and future terapia con ... · proton therapy: past, present and...

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