Diapositiva 1

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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
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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

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Boron Neutron Capture Therapy
Boron selectively accumulated in tumor cells
Neutrons from nuclear reactors

• 10B (n,?)7Li (? 3837 b)

(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.

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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,?)2H E? 2.2 MeV
?  0.33 b and reactor background
High complexity four components, each with
different LET and different RBE !!!
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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
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BNCT facility at NRI Rez (Prague)
Nuclear reactor power 9 MW
Epithermal neutron flux 7108 cm-2 s-1
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Thermal neutrons lt 0.4 eV Epithermal neutrons
0.4 eV lt En lt 10 keV Fast neutrons gt 10 keV
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Treatment room
Control room
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Fixation mask
12 cm diameter collimator
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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

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Tissue equivalent phantoms
Standard water phantom 50x50x25 cm3
Cylindrical water-equivalent phantom d 16cm, h
14cm
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Phantoms reproduced in MCNP5

• Neutron flux on the central plane
• Boron dose in 0.5 cm3 cells
• - Neutron dose along the beam axis

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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)
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Standard gel
Boron dose
Borated gel
Boron dose
Dose images (15x12 cm2) in the standard water
phantom
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Thermal neutron flux
Standard phantom
Fast neutron flux
Epithermal neutron flux
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Thermal neutron flux
Cylindrical phantom
Fast neutron flux
Epithermal neutron flux
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Boron dose distribution
Transverse profiles at 3 cm depth
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Boron dose distribution
Transverse profiles at in the cylindrical phantom
at different depths
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Boron dose distribution
In-depth on-axis profiles in the two phantoms
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Fast neutron and gamma doses separation
?(OD)st a1D? a2Dnp ?(OD)hw a3D? a4Dnd
f Dnd/Dnp 0.660.01
from Monte Carlo
Central profile in the standard water phanton.
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(1) Binns et al., Med Phys, 32 (12), 2005
Central profile in the standard water phantom.
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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