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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