GEANT4 simulation of an ocular proton beam & benchmark against MC codes

D. R. Shipley, H. Palmans, C. Baker, A. Kacperek

Monte Carlo 2005 Topical Meeting

Chattanooga, Tennessee, USA

17 - 21 April 2005

Overview of talk

• Introduction and advantages of proton therapy • Typical low-energy clinical proton therapy facility

62 MeV ocular proton beam at the Clatterbridge Centre for Oncology (CCO), UK

• GEANT4 simulations• Dose distributions for full-energy and modulated CCO

beam line and comparison with measurement• Key physical processes and dose distributions for 50,

150, 250 MeV monoenergetic beams• Conclusions and future work

Introduction

• Proton therapy is on the increase due to commercial availability of turnkey facilities and reduced cost

• Main treatment site is eye (melanoma) but more and more deep seated tumours

• Dosimetry is not as well established as for x-ray therapy; NPL has research projects for improved proton dosimetry

• Monte Carlo is essential for studying dosimetry, detector perturbation factors, stopping powers, etc.

Background: Improved therapy using protons versus x-rays

0 2 4 6 8z (cm)

0

20

40

60

80

100

pd

d

X - 10 MV

modulated

p - 100 MeV

non-modulated

Tumour

Principle of range modulation

z

Dw

CCO proton beam line – treatment room

CCO proton beam line – GEANT4 (VRML)

GEANT4 simulations: general

• GEANT4 6.2.p02 with Low Energy EM Physics package (G4EMLOW 2.3).

• Physics processes:– ICRU 49 parameterisation: proton energy loss (EM interactions)– LHEP and HEP models: hadronic processes (non-elastic

nuclear interactions)– recommended for use in medical applications (?)

• Cuts– 0.02 mm in phantom (<< dose scoring region), 10 mm

elsewhere– minimize any dependencies of particle transport on geometry

GEANT4: CCO beam line

• HadronTherapy (GEANT4):– calculates dose distributions in a PMMA phantom for the CCO

beam line– derived from the HadronTherapy advanced example distributed with

GEANT4– depth dose and lateral dose distributions – modulated and full-energy (no mod wheel) beams

• Comparison with:– McPTRAN.RZ: Palmans, NPL (2005)

and MCNPX– Film and diode measurements

Depth and lateral dose distributions in PMMA: CCO full-energy beam

Depth dose

0

0.2

0.4

0.6

0.8

1

1.2

0.0 0.5 1.0 1.5 2.0 2.5

Radius (cm)

No

rmal

ised

do

se (

arb

. un

its)

Measured: Film (average)

GEANT4

0

0.2

0.4

0.6

0.8

1

1.2

0.0 0.5 1.0 1.5 2.0 2.5

Radius (cm)

No

rmal

ised

do

se (

arb

. un

its)

Measured 1: Diode (average)

Measured 2: Diode (average)

Measured 3: Film (average)

GEANT4

Lateral dose:

front face

Lateral dose:

0.5 x r0

0

1

2

3

4

5

6

1.0 1.5 2.0 2.5 3.0

Depth in PMMA (cm)

No

rmal

ised

do

se @

3m

m d

epth

(ar

b. u

nit

s)

McPTRAN.RZMeasured 1 (from [23])Measured 2MCNPXGEANT4

Depth and lateral dose distributions in PMMA: CCO modulated beam

Depth dose

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.0 1.5 2.0 2.5 3.0

Depth in PMMA (cm)

No

rmal

ised

do

se @

3m

m d

epth

(ar

b. u

nit

s)

GEANT4

McPTRAN.RZ

Measured (from [23])

MCNPX

Lateral dose:

front face

Lateral dose:

0.5 x r0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.5 1.0 1.5 2.0 2.5

Radius (cm)

No

rmal

ised

do

se (

arb

. un

its)

Measured 1: Diode (average)

Measured 2: Diode (average)

Measured 3: Film (average)

GEANT4

0

0.2

0.4

0.6

0.8

1

1.2

0.0 0.5 1.0 1.5 2.0 2.5

Radius (cm)

No

rmal

ised

do

se (

arb

. un

its)

Measured: Film (average)

GEANT4

GEANT4: monoenergetic beams

• WaterPhantom (GEANT4)– calculates dose distributions in a water phantom for monoenergetic

pencil beams – depth dose : 200 cylindrical slabs on beam axis– radial dose : 100 annular rings (0.1 mm thick) at 0.5, 0.9 x r0– energy : scoring phase space data

at a plane – analysed with MATLAB– 50, 150, 250 MeV pencil proton beams

• Comparison with:– PTRAN: Berger, NIST (1993)– MCNPX v2.5d (beta): LANL (2004)– SRIM v2003.12: Ziegler (2003)

Influence of key processes on depth dose distributions

0

20

40

60

80

100

120

140

160

180

0.86 0.88 0.9 0.92 0.94 0.96 0.98 1 1.02z/r0

dE

/dx

(MeV

g-1

cm

2)

CSDA

0

20

40

60

80

100

120

140

160

180

0.86 0.88 0.9 0.92 0.94 0.96 0.98 1 1.02z/r0

dE

/dx

(MeV

g-1

cm

2)

CSDA

+ energy straggling

0

5

10

15

20

25

30

35

40

0.86 0.88 0.9 0.92 0.94 0.96 0.98 1 1.02z/r0

dE

/dx

(MeV

g-1

cm

2)

CSDA

+ energy straggling

0

5

10

15

20

25

30

35

40

0.86 0.88 0.9 0.92 0.94 0.96 0.98 1 1.02z/r0

dE

/dx

(MeV

g-1

cm

2)

CSDA

+ energy straggling

+ multiple scattering

0

5

10

15

20

25

30

35

40

0.86 0.88 0.9 0.92 0.94 0.96 0.98 1 1.02z/r0

dE

/dx

(MeV

g-1

cm

2)

CSDA

+ energy straggling

+ multiple scattering

+ nuclear interactions

0

5

10

15

20

25

30

35

40

0 0.2 0.4 0.6 0.8 1z/r0

dE

/dx

(MeV

g-1

cm

2)

CSDA

+ energy straggling

+ multiple scattering

+ nuclear interactions

Influence of key processes on lateral dose distributions

1E-03

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

0.0 0.5 1.0 1.5 2.0

r (cm)

Do

se (

a.u

.)

CSDA

1E-03

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

0.0 0.5 1.0 1.5 2.0

r (cm)

Do

se (

a.u

.)

CSDA

+ multiple scattering

1E-03

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

0.0 0.5 1.0 1.5 2.0

r (cm)

Do

se (

a.u

.)

CSDA

+ multiple scattering

+ energy straggling

1E-03

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

0.0 0.5 1.0 1.5 2.0

r (cm)

Do

se (

arb

. u

nit

s)

CSDA

+ multiple scattering

+ energy straggling

+ nuclear interactions

Depth dose distributions in water:monoenergetic beams

0

20

40

60

80

100

1.5 2 2.5Depth in water (cm)

Do

se p

er in

cid

ent

flu

ence

(MeV

cm

2 g

-1 p

er p

roto

n)

MCNPX-50MeV

GEANT4-50MeV

PTRAN-50MeV

SRIM-50MeV

0

10

20

30

40

10 12 14 16 18

Depth in water (cm)

Do

se p

er in

cid

ent

flu

ence

(MeV

cm

2 g

-1 p

er p

roto

n)

MCNPX-150MeV

GEANT4-150MeV

PTRAN-150MeV

SRIM-150MeV

0

5

10

15

20

25

25 30 35 40

Depth in water (cm)

Do

se p

er in

cid

ent

flu

ence

(MeV

cm

2 g

-1 p

er p

roto

n)

MCNPX-250MeV

GEANT4-250MeV

PTRAN-250MeV

50 MeV

150 MeV

250 MeV

Stopping power

Energy loss straggling

Nuclear interaction

GEANT4 ICRU 49(param. model)

Bohr / Vavilov / Landau

LHEP / HEP

MCNPX ICRU 49 Vavilov LA150

PTRAN ICRU 49 Vavilov ICRU 63

SRIM Ziegler et al. ? -

Lateral dose distributions in water:monoenergetic beams

0.1

1.0

10.0

100.0

1000.0

10000.0

100000.0

0.0 0.2 0.4 0.6 0.8

Radius (cm)

Do

se (

MeV

g

-1 p

er p

roto

n)

MCNPX-050MeV

MCNPX-150MeV

MCNPX-250MeV

GEANT-050MeV

GEANT-150MeV

GEANT-250MeV

PTRAN-050MeV

PTRAN-150MeV

PTRAN-250MeV

0.1

1.0

10.0

100.0

1000.0

10000.0

0.0 0.5 1.0 1.5 2.0

Radius (cm)

Do

se (

MeV

g

-1 p

er p

roto

n)

MCNPX-050MeV

MCNPX-150MeV

MCNPX-250MeV

GEANT4-050MeV

GEANT4-150MeV

GEANT4-250MeV

PTRAN-050MeV

PTRAN-150MeV

PTRAN-250MeV

0.5 x r0

0.9 x r0

Multiple scattering

Nuclear interaction

GEANT4 Lewis LHEP / HEP

MCNPX Goudsmit & Sanderson

LA150

PTRAN Molière ICRU 63

Summary and conclusions

• GEANT4: low-energy clinical proton beam (CCO):– full-energy beam:

• overestimates Bragg peak by ~20%

– modulated beam: • increasing depth dose profile with distinctive peak• sharper penumbra and ‘horns’ at edge of lateral dose profile

– some dependence on GEANT4 models, daily beam variations and type of detector

• GEANT4: monoenergetic proton beams (clinical energies)– different physical models (or their implementation) in the MC codes

give distinct differences in dose distributions at these energies– improvements in GEANT4 model used is still needed (or a better

physical model chosen)

Future work

• Proton stopping powers for clinical beams:– directly using Monte Carlo– from fluence spectra at depth

• Perturbation factors for detectors• Graphite-to-water conversion factors

– proton calorimetry (NPL)