Valeria Conte, Paolo Colautti, Marco Poggi, Stefania ...microdos/0004.pdfValeria Conte, Paolo...
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Valeria Conte, Paolo Colautti, Marco Poggi, Stefania Canella, Gastone Donà, Giampietro Egeni, Mariano Lombardi, Laura De Nardo, Davide Moro, Giorgio Tornielli, Bernd Großwendt INFN-LNL INFN-PD, Padova University V. Conte, ION BEAMS ‘12
Transcript of Valeria Conte, Paolo Colautti, Marco Poggi, Stefania ...microdos/0004.pdfValeria Conte, Paolo...
Valeria Conte, Paolo Colautti, Marco Poggi, Stefania Canella, Gastone Donà,
Giampietro Egeni, Mariano Lombardi, Laura De Nardo, Davide Moro, Giorgio Tornielli,
Bernd Großwendt
INFN-LNL
INFN-PD, Padova University
V. Conte, ION BEAMS ‘12
Valeria Conte, Paolo Colautti, Marco Poggi, Stefania Canella, Gastone Donà,
Giampietro Egeni, Mariano Lombardi, Laura De Nardo, Davide Moro, Giorgio Tornielli,
Bernd Großwendt
INFN-LNL
INFN-PD, Padova University
V. Conte, ION BEAMS ‘12
To investigate experimentally
and by Monte Carlo
simulations the ionization
pattern of different light ions of
therapeutic interest, in a
nanometre-sized volume
copyright: - www.cellbio.utmb.edu - www.people.virginia.edu
The “true“ target volumes of life science are of
nanometre dimensions
The real target
volumes of radiobio-
logy and, therefore,
also of radiation
physics are the
volumes of sub-
cellular structures
(ii) Diameter of a chromatin fibre: 30 nm
(i) Diameter of a chromosome: 300 nm
(iii) Diameter of a nucleosome: 10 nm
(iv) Diameter of the DNA: 2.3 nm
copyright: - www.cellbio.utmb.edu - www.people.virginia.edu
The “true“ target volumes of life science are of
nanometre dimensions
The real target
volumes of radiobio-
logy and, therefore,
also of radiation
physics are the
volumes of sub-
cellular structures
(ii) Diameter of a chromatin fibre: 30 nm
(i) Diameter of a chromosome: 300 nm
(iii) Diameter of a nucleosome: 10 nm
(iv) Diameter of the DNA: 2.3 nm
The likelihood of damage is most probably related to
the stochastics of particle interactions in such sub-
cellular structures.
The likelihood of biological damage increases with decreasing
distance between particle interaction points (D. T. Goodhead, 1994)
2.72 keV electron 5 MeV proton
20 MeV He2+-ion 60 MeV C6+-ion
10
0 n
m t
rack s
eg
men
ts i
n w
ate
r LET= 6.4 kev/µm LET= 7.9 kev/µm
LET= 31.4 kev/µm LET= 292.5 kev/µm
Particles of different quality (charge state and velocity)
exhibit different interaction pattern.
20 nm
The likelihood of biological damage increases with decreasing
distance between particle interaction points (D. T. Goodhead, 1994)
2.72 keV electron 5 MeV proton
20 MeV He2+-ion 60 MeV C6+-ion
10
0 n
m t
rack s
eg
men
ts i
n w
ate
r LET= 6.4 kev/µm LET= 7.9 kev/µm
LET= 31.4 kev/µm LET= 292.5 kev/µm
Particles of different quality (charge state and velocity)
exhibit different interaction pattern.
20 nm
Nanodosimetry takes a ‘picture’ of the track structure
of particles at different radiation qualities.
The Typical Structure of a Track Segment
of a Light Ion
F
It is characterized by a
more or less straight
primary particle
component, and by
the sub-tracks of
secondary electrons
V. Conte, ION BEAMS ‘12
FThe track component
due to primary-particle
interactions:
Track-core region
The track component
due to secondary-
particle interactions:
Penumbra region
Track Structure: track-core and penumbra region
We want to investigate the track-core and the
penumbra region separately
The Measurement of Track-structure Properties:
Geometry of the Experiment
A narrow primary particle beam of radiation quality Q
is passing a cylindrical target volume of diameter D, at
a distance d
D
d
and the number of
ionizations in the
volume is counted
d-electron d-electron
d-electron
primary trajectory
The MSAC
The drift column
The sensitive volume V
V. Conte, ION BEAMS ‘12
The STARTRACK device
A cylinder 3.7 mm in diameter
and height filled with 3 mbar of
propane, simulates at density
1 mg/cm3 a diameter
D = 20 nm
The MSAC
The drift column
The sensitive volume
V. Conte, ION BEAMS ‘12
The STARTRACK device
N = electrons 1 2 3 4 5 6 7 8 9 10 11
Single ionizing particle.
Single electron counting.
Measurable quantity:
cluster size n = number of ionizations
produced inside V by single passage of
an ionizing particle
Pn(d) is the probability distribution of
cluster size n , for ionizing particles
crossing or passing by V at impact
parameter d.
Pn(Q
)
Cluster-size distributions: track-core region
V. Conte, ION BEAMS ‘12
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20 25 30
1H, 20 MeV, ( )
ion= 2 mg/cm
2
2H, 16 MeV, ( )
ion= 1 mg/cm
2
6Li, 48 MeV, ( )
ion= 0.1 mg/cm
2
7Li, 26.7 MeV, ( )
ion= 0.05 mg/cm
2
Cluster size n
Pn(Q
)
Cluster-size distributions: track-core region
V. Conte, ION BEAMS ‘12
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20 25 30
1H, 20 MeV, ( )
ion= 2 mg/cm
2
2H, 16 MeV, ( )
ion= 1 mg/cm
2
6Li, 48 MeV, ( )
ion= 0.1 mg/cm
2
7Li, 26.7 MeV, ( )
ion= 0.05 mg/cm
2
Cluster size n
Pn(Q
)
Cluster-size distributions: track-core region
Sparsely ionizing particles, like 20 MeV protons, and
densely ionizing particles, like 26.7 MeV 7Li-ions, show
markedly different ionization patterns
With decreasing ionization mean free path length of the
primary ions the distributions become peaked and shift
to larger cluster sizes
V. Conte, ION BEAMS ‘12
Pn(Q
)
Cluster-size distributions in the penumbra region
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20
protons, 20 MeV
6Li-ions, 48 MeV
7Li-ions, 26.7 MeV
12C, 96 MeV
Cluster size n
d = 2.2 mg/cm2
V. Conte, ION BEAMS ‘12
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20
protons, 20 MeV
6Li-ions, 48 MeV
7Li-ions, 26.7 MeV
12C, 96 MeV
Cluster size n
d = 2.2 mg/cm2
Pn(Q
) P
n(Q
)
Cluster-size distributions in the penumbra region
exhibit the same shape, irrespectively of radiation
quality (charge state and velocity).
V. Conte, ION BEAMS ‘12
Cluster-size distributions in the penumbra region
Pn(Q
) / (D
/io
n)
V. Conte, ION BEAMS ‘12
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20
protons, 20 MeV
6Li-ions, 48 MeV
7Li-ions, 26.7 MeV
12C, 96 MeV
Cluster size n
d = 2.2 mg/cm2
The characteristics of d-electrons
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20
protons, 20 MeV
6Li-ions, 48 MeV
7Li-ions, 26.7 MeV
12C, 96 MeV
Cluster size n
d = 2.2 mg/cm2
V. Conte, ION BEAMS ‘12
Pn(Q
) / (D
/io
n)
The characteristics of d-electrons
When divided by the average number of primary
ionizations along a length D, the cluster-size
distributions become an almost unique curve.
d-electron effectiveness is almost independent of
primary radiation quality
Pn(Q
)
V. Conte, ION BEAMS ‘12
10-6
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20
d = 1.6 mg/cm2
d = 1.9 mg/cm2
d = 2.2 mg/cm2
d = 2.5 mg/cm2
d = 3.0 mg/cm2
d = 3.6 mg/cm2
Cluster size n
12C, 96 MeV
Dependence on impact parameter
10-6
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20
d = 1.6 mg/cm2
d = 1.9 mg/cm2
d = 2.2 mg/cm2
d = 2.5 mg/cm2
d = 3.0 mg/cm2
d = 3.6 mg/cm2
Cluster size n
12C, 96 MeV
Pn(Q
)
Cluster size distributions in the penumbra region exhibit
the same shape, irrespectively of impact parameter.
If the impact parameter is increased , the relative
cluster-size probability Pn≥1(Q) decreases, mainly due to
the decrease of the solid angle
V. Conte, ION BEAMS ‘12
Dependence on impact parameter
10-6
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20
d = 1.6 mg/cm2
d = 1.9 mg/cm2
d = 2.2 mg/cm2
d = 2.5 mg/cm2
d = 3.0 mg/cm2
d = 3.6 mg/cm2
Cluster size n
12C, 96 MeV
Pn(Q
)x(d
)2
Cluster-size distributions scaled to the same site solid
angle form an almost unique curve.
d-electron effectiveness is almost independent of impact
parameter.
V. Conte, ION BEAMS ‘12
d-electron characteristics: invariance with impact parameter
Pn(Q
)
V. Conte, ION BEAMS ‘12
10-6
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20 25 30
1H, 20 MeV, d = 0 mg/cm
2
7Li 26.7 MeV
1H, 20 MeV, d = 2.2 mg/cm
2
7Li 26.7 MeV
Cluster size n
The d-electrons’ contribution is almost negligible
10-6
10-5
10-4
10-3
10-2
10-1
100
0 5 10 15 20 25 30
1H, 20 MeV, d = 0 mg/cm
2
7Li 26.7 MeV
1H, 20 MeV, d = 2.2 mg/cm
2
7Li 26.7 MeV
Cluster size n
Pn(Q
)
The d-electrons’ contribution is almost negligible
The frequency of high clustering due to d-electrons is
almost negligible compared to that of the primary particle,
especially for densely ionizing particles.
V. Conte, ION BEAMS ‘12
The consequence
The physics behind radiation effectiveness
V. Conte, ION BEAMS ‘12
Assumption: radiation effectiveness is closely related to
ionization clustering in a 20 nm site
The physics in a 20 nm site:
the relative contribution of the tracks of d-electrons alone
to induce clustered ionizations is
I. almost negligible, and
II. substantially irrespective of radiation quality and of
impact parameter.
the radiation effectiveness in producing complex damage is
mainly related to ionizing collision events of the primary ion
together with short range electrons surrounding the ion track.
The ionization mean free path of primary particles seems to be
a good quantity to describe the radiation quality of ionizing
particles.
