Dosimetry for proton therapy

Hugo Palmans, PhD, FInstP Principle Research Scientist

Radiation Dosimetry group

National Physical Laboratory

2nd December 2013

Acknowledgments

NPL colleagues: Mark Bailey, Hugo Bouchard, David Crossley, Simon Duane,

Kamran Fathi, Sebastian Galer, Nigel Lee, Bo Li, Hugo

Palmans, Lauren Petrie, Giuseppe Schettino, Séverine

Rossomme, Peter Sharpe, David Shipley, Russell Thomas

Collaborators: Clatterbridge Cancer Centre: Andrzej Kacperek

University of Surrey: Andy Nisbet, Karen Kirkby

Université Catholique de Louvain: Stefaan Vynckier

Ion Beam Applications (IBA): Damien Betrand

University of Århus: Niels Bassler, Rochus Herrmann, Armin Luhr

University of Birmingham: Dan Kirby, Stuart Green

University College of London: Gary Royle

University of Stockholm: Pedro Andreo

…

Overview

Physical characteristics of proton beams and

consequences for dosimetry

Physical advantage of protons

r o,p = 1mm r o,e = 1mm

Stopping powers – protons versus

electrons

100

101

102

103

10-6 10-4 10-2 100 102

t = E k /E rest

S co

ll / r

(M

eV

cm

2 g

-1 )

proton water

protons air

electrons water

electrons air

0.90

1.00

1.10

1.20

1.30

s w

,air

sw,air protons

sw,air electrons

ICRU 49 ICRU 37

Consequence 1

Ionisation in air ±~ dose to water

Consequence 2: high-LET

component

Kempe et al. (2007) Med. Phys. 34:183-92

0.0

5.0

10.0

15.0

20.0

0 5 10 15 20 25 30

depth in water / g cm -2

en

erg

y l

os

s p

er

un

it d

ep

th /

Me

V c

m 2

g -1

total 1 H

primary 1 H

secondary 1 H secondary

1 H <10 eV/nm

> 2 eV/nm

> 6 eV/nm

> 10

eV/nm > 20

eV/nm

< 2 eV/nm

Consequence 2.1: chemical heat

defect in water calorimeters

0,0

1,0

2,0

3,0

LET (keV.mm-1)

G (

10

0 e

V-1

)

10-1 100 101 102

H+

OH•

e¯aq

H•

OH¯

H2

HO2

H2O2

60Co (100 MeV) (1MeV)

protons

-1

0

1

2

3

4

5

6

7

0 20 40 60 80 100 120 140

LET / keV mm-1

ch

em

ica

l h

ea

t d

efe

ct /

%

p d

He C

Brede et al (2006) Phys. Med. Biol.

Consequence 2.2: initial ion

recombination

Air-filled IC Liquid-filled IC

Palmans et al (2006) Phys. Med. Biol. 51:903 FJ Kaiser (2013) PhD university Aarhus

Consequence 2.3: signal

quenching solid-state detectors

Birmingham 15 MeV beam

CERN anti-proton beam

GSI 12C ion beam

Bassler et al. 2008

Herrmann et al. 2011

Electron slowing down spectrum 200 MeV proton beam, z = 20 cm

(Medin and Andreo 1997, Phys Med Biol 42:89-105)

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03

energy / MeV

pa

rtic

le f

lue

nc

e p

er

inc

ide

nt

pro

ton

/ M

eV

-1 c

m -2

proton

electrons

Consequence: secondary

electron perturbations

1.000

1.002

1.004

1.006

0 50 100 150 200 250

proton energy / MeV

pw

all

0.998

0.999

1.000

A150

graphite

1.000

1.002

1.004

1.006

1.008

0 50 100 150 200 250

proton energy / MeV

pw

all,

A15

0 /

pw

all,

C

A150

Palmans et al. 2001 - ND,w based

Palmans et al. 2001 - NK based

average

0.997

0.998

0.999

1.000

1.001

0 50 100 150 200 250

proton energy / MeV

pce

l

aluminium central electrode graphite central electrode

0.994

0.996

0.998

1.000

1.002

0 50 100 150 200 250

proton energy / MeV

pce

l,A

l / p

cel,

C

Monte Carlo

Medin et al. 1995

Palmans et al. 2001 - ND,w-based

Palmans et al. 2001 - NK-based

Palmans et al. (2011) Proc IDOS, IAEA-CN182-230

Scattering – protons versus photons

(Palmans 2006, Scope 15:5-12)

Consequence: difficulty of

fluence based dosimetry

N protons A

r =

med

med

S

A

N D

guard

collecting electrode housing entrance

window

winding

N protons

Beam scanning

Consequence 1: Potential revival

of fluence based dosimetry

Large area ion chamber: pdd(z)

Faraday cup: N/MU

S/ρ: dd(z0 or zref)

Integrate lateral dose profiles over all spots

Consequence 2: Graphite

calorimetry

Core

Inner jacket

Outer jacket

Annular PCB

Graphite vacuum body

Palmans et al (2004)

Phys Med Biol 49:3737

Consequence 2: Graphite

calorimetry – heat

transfer within core

18

0.0

0.5

1.0

1.5

2.0

2.5

3.0

100 110 120 130 140

tem

pera

ture

ris

e /

mK

time / s

thermistor 1

thermistor 2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

100 105 110 115 120 125 130 135 140

tem

pera

ture

ris

e /

mK

time / s

thermistor 1

thermistor 2

1.0

1.2

1.4

1.6

1.8

2.0

104 105 106 107 108

tem

pera

ture

ris

e /

mK

time / s

thermistor 1

thermistor 2

1.0

1.2

1.4

1.6

1.8

2.0

104 105 106 107 108

tem

pera

ture

ris

e /

mK

time / s

thermistor 1

thermistor 2

Consequence 3: Ion

recombination Analogy IMRT beams: Palmans et al. 2010 Med. Phys. 37 2876-2889

dxdti

dxdti

V

B

V

AP

sat

sat

ion

2

21

offset

1.024 1.009 250 MeV

1.015 1.006 60 MeV

Gauss Rectangle

Scan direction

0.95

1.00

1.05

1.10

0 1 2 3 4 5 6 7

position #

rela

tiv

e v

olu

me

re

co

mb

ina

tio

n 60 MeV

250 MeV

Projectile fragmentation (ions)

In peripheral collisions

In head-on collisions

12C 11C

12C

4He

4He

4He

Consequence 1: dose conversion

graphite calorimetry

0.60

0.70

0.80

0.90

1.00

1.10

1.20

0 50 100 150 200 250

proton energy / MeV

(L/ r

)w,g

or

(<E

>

/A)w

,g

Stopping power ratio

Total non-elastic absorption

Emitted protons

Emitted deuterons Emitted alpha particles

w

g

ggww

SzDzD

=r

)()( ?

Consequence 1: dose conversion

graphite calorimetry 60 MeV protons 200 MeV protons

22

experiment

0.960

0.980

1.000

1.020

1.040

1.060

0.0 5.0 10.0 15.0 20.0 25.0

z w-eq / g cm-2

kfl o

r k

'fl

p

all charged

thick lines = k f l from fluence

symbols = k 'f l from fluence

thin lines = k f l from dose calculation

Palmans et al (2013) Phys. Med. Biol. 58:3481-3500

Consequence 2: PET verification

Parodi et al

Consequence 3:

tissue-equivalence

Palmans et al. (2005) Phys. Med. Biol. 50:991-1000

Conclusions

Physical characteristics of protons affect dosimetry

Scanned proton beams need new adapted

approaches for dosimetry

NPL is world leading NMI in proton dosimetry;

working on primary standards, relative dosimetry,

micro- and nano-dosimetry