MONTE CARLO SIMULATIONS ON
NEUTRON TRANSPORT AND ABSORBED
DOSE IN TISSUE-EQUIVALENT
PHANTOMS EXPOSED TO HIGH-FLUX
EPITHERMAL NEUTRON BEAMS
G. Bartesaghi, G. Gambarini, A. Negri
Department of Physics of the University of Milan and INFN, Milan, Italy
J. Burian, L. Viererbl
Department of Reactor Physics, Nuclear Research Institute Rez, Czech Republic
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Outline
• Boron Neutron Capture Therapy (BNCT):
a brief introduction
• Dosimetry and treatment planning in BNCT
• NRI-Rez BNCT facility
• Materials & Method:
•MC simulations: source and phantoms
description
• Fricke gel dosimeters
• Results and conclusions
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Boron Neutron Capture Therapy
Boron selectively
accumulated in
tumor cells
Neutrons from nuclear reactors
10B
(n,)7Li
( = 3837 b)
Gamma
10B
1n
11B*
7Li
4He
(477 keV)
Emission of low range, high LET ions:
4He2+ (1.47 MeV)
7Li3+ (0.84 MeV)
with a range in tissue about one cell diameter.
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Dosimetry in BNCT
What has to be measured?
Dtot
II
DB
+
Dp
+
Dn
+
D
“therapeutic dose”, from 10B(n,)7Li
 = 3837 b
from 14N(n,p)14C Ep= 630 keV
 = 1.9 b
due to epithermal and fast neutron scattering
mainly on H nuclei
from 1H(n,γ)2H
Eγ = 2.2 MeV
and reactor background
 = 0.33 b
High complexity: four components, each with different LET and different RBE !!!
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Three distinct modules are necessary:
- dosimetry with an appropriate phantom
- Monte Carlo based treatment planning (TP)
- 10B concentration on-line monitoring
Treatment planning in BNCT
Reactor
geometry
Patient anatomical
images
Boron
concentration
TP software should be
capable to display isodose
curves, superimposed to the
anatomical images
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
BNCT facility at NRI – Rez (Prague)
LVR-15 reactor
Nuclear
reactor
power:
Epithermal column
9 MW
Epithermal
neutron flux:
7∙108 cm-2 s-1
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Thermal neutrons: < 0.4 eV
Epithermal neutrons: 0.4 eV < En < 10 keV
Fast neutrons: > 10 keV
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Treatment
room
Control
room
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Fixation
mask
12 cm
diameter
collimator
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
MC calculations
Radiation transport and interactions in tissue-equivalent phantoms
- Neutron transport and thermalization
- Boron dose
- Neutron dose
MCNP5 code
Source plane technique
(used with MacNCTPLAN):
- energy distribution
- radial distribution
- divergence distribution
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Tissue equivalent phantoms
Standard water phantom
50x50x25 cm3
Cylindrical waterequivalent phantom
d: 16cm, h: 14cm
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Phantoms reproduced in MCNP5
-Neutron flux on the central plane
- Boron dose in 0.5 cm3 cells
- Neutron dose along the beam axis
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Fricke Gel dosimeters in form of layers
 Fricke solution + Xylenol Orange = radiochromic
 very good tissue equivalence
 thin layers (up to 3mm thick):
• not affecting the in-phantom neutron
transport
• it is possible to modify the gel composition in
order to achieve dose components separation
Standard Gel
-rays and fast neutrons (recoil-protons)
Standard-Gel added with 10B (40 ppm)
-rays, fast neutrons,  and 7Li particles
Gel like Standard-Gel made with heavy water
-rays and fast neutrons (recoil-deuterons)
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Standard gel
Boron
Borated
dose
gel
Boron dose
Dose images
(15x12 cm2) in the
standard water
phantom
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Thermal neutron flux
Standard
phantom
8
-1
-2
Flux (cm s )
4x10
8
3x10
Fast neutron flux
8
2x10
8
4
8
7
4x10
7
3x10
-1
4 6
8 10
Depth
12 14 -8
(cm)
-2
Flux (cm s )
2
0
-4
Wid
0
th (
cm
)
1x10
7
2x10
Epithermal neutron flux
7
1x10
8
8
)
m
8
3x10
8
2x10
8
1x10
)
h
(c
m
0
2 4
6 8
-4
Dept
10
h (cm
12
14 -8
)
id
t
0
8
4
W
-1
-2
Flux (cm s )
W
id
t
h
4x10
0
2 4
6 8
-4
Dept
10
h (cm
12
14 -8
)
(c
0
4
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Thermal neutron flux
Cylindrical
phantom
8
8
3x10
Fast neutron flux
8
2x10
8
4
8
1x10
th (
4 6
8 10
Depth
12 14 -8
(cm)
7
3x10
-1
-2
Flux (cm s )
2
0
-4
Wid
0
7
4x10
cm
)
-1
-2
Flux (cm s )
4x10
7
2x10
Epithermal neutron flux
7
1x10
8
)
m
W
8
3x10
8
2x10
8
1x10
8
(cm
10
)
-4
12
14 -8
)
m
(c
0
h
2 4
6
Dep
th
idt
0
8
4
W
-1
-2
Flux (cm s )
id
t
h
0
2 4
6 8
-4
Dept
10
h (cm
12
14 -8
)
(c
0
8
4x10
4
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Boron dose distribution
14
12
Dose Rate (Gy/h)
Gel data
MC data
Standard
phantom
10
8
6
Cylindrical
phantom
4
2
0
-8
-6
-4
-2
0
2
4
6
8
10
Width (cm)
Transverse profiles at 3 cm depth
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Boron dose distribution
14
Gel data
MC data
Cylindrical phantom
12
Dose Rate (Gy/h)
2.75 cm
10
8
5.75 cm
6
4
8.75 cm
2
0
-8
-6
-4
-2
0
2
4
6
8
Width (cm)
Transverse profiles at in the cylindrical
phantom at different depths
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Boron dose distribution
14
Gel data
MC
10
8
6
4
2
Cylindrical phantom
12
Dose rate (Gy/h)
12
Dose rate (Gy/h)
14
Standard phantom
Gel data
MC data
10
8
6
4
2
0
0
0
2
4
6
8
10
Depth (cm)
12
14
0
2
4
6
8
10
12
14
Depth (cm)
In-depth on-axis profiles
in the two phantoms
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Fast neutron and gamma doses separation
(OD)st = α1Dγ + α2Dnp
(OD)hw = α3Dγ + α4Dnd
0,45
0,40
Standard gel
Heavy water gel
f = Dnd/Dnp
from Monte
Carlo
= 0.66±0.01
0,30
0,25
0,20
0,70
0,15
0,69
0,10
0
2
4
6
8
10
0,68
12
Depth (cm)
Central profile in the
standard water phanton.
Dd / Dp
(OD)
0,35
0,67
0,66
0,65
0
2
4
6
8
10
12
14
Depth (cm)
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
9
Gamma dose (gel)
Gamma dose (TLD)
Fast neutrons dose (gel)
Fast neutrons dose (IC)
8
Dose rate (Gy/h)
7
6
5
4
3
2
1
0
0
2
4
6
8
10
12
14
Depth (cm)
(1) Binns et al., Med Phys, 32 (12), 2005
Central profile in the standard water phantom.
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009
Conclusions
• Neutron transport, boron dose and neutron
dose in tissue-equivalent phantoms have been
calculated
• Boron and fast neutron doses have been
measured by means of Fricke gel layers
• The good agreement confirms the accuracy of
the source model used for TP
G. Bartesaghi, 11° ICATPP, Como, 5-9 October 2009