study of a dd compact neutron generator for bnct
DESCRIPTION
Study of a DD compact neutron generator for BNCT. Elisabetta Durisi Lorenzo Visca. Collaborations. The research activity is performed in the mainframe of : - PowerPoint PPT PresentationTRANSCRIPT
[email protected], [email protected] - April 18th, 2005 1
Study of a DD compact neutron generator for BNCT
Elisabetta Durisi
Lorenzo Visca
[email protected], [email protected] - April 18th, 2005 2
Collaborations
The research activity is performed in the mainframe of:
"Terapie oncologiche innovative basate sulla cattura di neutroni (NCT) con nuove tipologie di sorgenti di neutroni e di molecole-target a base di Boro e
Gadolinio"
supported by Azienda Ospedaliera San Giovanni Battista A.S. (dipartimento Oncologia) and included in the Oncology Program financed by Compagnia di San Paolo.
• Lawrence Berkeley National Laboratory (Accelrator & Fusion division)
• Experimental Physics Department, University of Turin
• S. Giovanni Battista Hospital Torino, Italy – Molinette Hospital Torino, Italy
• INFN section of Turin, Italy
• ENEA (Frascati - Bologna)
• EUROSEA, Turin
• Nuclear Energy Department, Polytechnic of Milan
• Chemistry Department, University of Turin
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Neutron Sources
Epithermal neutron (0.4 eV - 10 keV) beams are available from existing nuclear reactors.
Charged-particle accelerators, compact neutron generators and hospital radiotherapy facilities for BNCT (PHONES, INFN project) are now under development.
Epithermal neutrons lose energy in the patient body and become capturable slow neutrons while proceeding to the tumour.
Cell-killing 10B-Capture
in Tumour
Neutron sources
Moderator Material
Tissue (moderator)
fast neutrons
epithermal neutrons
slow neutrons
Within patient’s body
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RF-Induction Antenna
DD compact neutron generator developed by LBNL - accelerator and fusion division
• A 13.56 MHz radio frequency (RF) discharge is used to produce deuterium ions.
• The ion beam is accelerated to energy of 120 kV.
• The beam impinges on a titanium coated aluminum target where neutrons are generated through D-D fusion reaction:
D+D 3He + n (2.45 MeV)
High Voltage Shield
Target Water Manifold
Al2O3 High Voltage Insulator
Target Cylinder
Secondary Electron Filter Electrode
Ion Source
Vacuum Chamber
RF-Antenna Guide Vacuum Pump
45 cm
60 cm
gas in
RF-Induction Antenna
Turbo pumping systemRoughing pump (up to 2 10-3 mbar)Turbo pump (<10-10 mbar)
HV power supply120 kV – 300 mA
HV relay
Pressure gauge controllers
RF power supply and matching network (freq. 13.56 MHz, max. transfer power 5000 W) Deuterium
gas flow system
Water cooling(2 lines: 1- Low conductance water for target 2- standard water for void system, RF system, HV power supply system.
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Installation
December 2004
The compact neutron generator has been installed in the former irradiation room of the synchrotron laboratory at the Physics InstituteTEST:
• low neutron flux,
GOAL:
• maximum neutron flux for BNCT application,
• final moderator design.
Al3O2 insulator
Vacuum pumping chamber
High voltage flange and target assembly
Minimum neutron yield (from agreement with LBNL) > 1011 s-1
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GOAL - Final moderator design: Beam Shaping Assembly (BSA)
Neutrons produced from DD fusion reaction (2.45 MeV) need to be moderated to lower energies for use in BNCT:
1. maintaining adequate beam flux,
2. minimizing undesired dose to the patient’s body and other non-tumour locations.
The major components of BSA are:
MODERATOR REFLECTOR DELIMITERGamma
shielding
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Assessment of a “good” BSA and comparison between different configurations
Evaluation of FIGURES OF MERIT
IN-PHANTOM FIGURES OF MERIT: calculation of depth dose profiles in healthy and
tumour tissue
FREE BEAM
PARAMETERS
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BSA with MCNP: EXAMPLE
Teflon= 1 cm
Al2O3
Target: Al, water cooling inside target
and Fe outsideBismuth Extraction grid +
water pipes
Copper Plasma chamber + water cooling
RF antenna: quartz outside,
water inside
Lithiated polyethylene= 5 cm
MgF2
Air
y
xLead + Antimony
Al
AlF3
AlF3
y
z
Epithermal column: 19 cm MgF2 + 6.5 cm Al + 10 cm MgF2 + 5 Al + 5 air; beam exit window 20x20 cm2
Distance: center of the source-beam exit window = 80 cm
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epith [cm-2 s-1] 2.41E6 1.2E8 1E8-1E9
Jepith [cm-2 s-1] 1.46E6 7.3E7
Df / epith [Gy cm2] 1.87 E-12 1.87 E-12 < 2E-13
D /epith [Gy cm2] 3.42 E-13 3.42 E-13 < 2E-13
Jepith/epith 0.607 0.607 >= 0.7
Free beam parameters
Recommended values for brain tumour treatment IAEA-TECDOC-1223
Neutron yield 1011 n/s- 120 kV, 300 mA Neutron yield 5 1012 n/s-160 kV, 1 A
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Neutron spectra (Neutron yield 1011 n/s)
Neutron Spectra at the beam exit window
0,00E+00
1,00E+04
2,00E+04
3,00E+04
4,00E+04
5,00E+04
6,00E+04
7,00E+04
8,00E+04
1,00E-09 1,00E-08 1,00E-07 1,00E-06 1,00E-05 1,00E-04 1,00E-03 1,00E-02 1,00E-01 1,00E+00 1,00E+01
Neutron energy [MeV]
neu
tro
n f
lux
[cm
-2 s
-1]
Config: MgF2+Al+MgF2+Al
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In phantom figures of merit
• Gamma dose “D”, combination of the doses deriving from
the beam and the photons induced by 1H(n,)2H capture reaction with the hydrogen in tissue.
• Hydrogen dose “DH” or fast neutron dose due to proton-
recoil reactions at the higher neutron energies (> 1 keV) in the tissue.
• Thermal neutron dose “DN”, due to the thermal neutron
capture mainly by nitrogen nuclei 14N(n,p)14C.
• Boron dose “DB” , due to neutron capture reaction with
boron.
Biological dose = DW = w D + wn (DH + DN) + wB DB
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Material RBE for (w)
RBE for n (wn)
10B (ppm) 10B CBE (wB)
Skin 1 3.2 15 2.5
Soft tissue 1 3.2 10 2.5
Healthy liver tissue
1 3.2 10 1.3
Tumour liver tissue
1 3.2 60 3.8
Values used in all the simulations
These are the weighting factors commonly used for brain tumour
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BSA with MCNP: EXAMPLE
yx
Cross section of the Anthropomorphic phantom ADAM
Liver segmentationSKIN ON TRUNK
RIB CAGE SURFACE
ARM BONES
ICRU reference phantom
implemented in MCNP by ENEA – Bologna
SPINE
STOMACH
SPLEEN
KIDNEYS
PANCREAS
BLADDER
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Total dose rate in healthy and tumour tissue
0,00E+00
5,00E-04
1,00E-03
1,50E-03
2,00E-03
2,50E-03
3,00E-03
3,50E-03
4,00E-03
4,50E-03
0 2 4 6 8 10 12 14
Depth in trunk [cm]
Dos
e ra
te [G
y-eq
/min
]
boron healthy tissue
gamma
tot healthy tissue
boron tumour tissue
tot tumour tissue
10B 15 ppm in skin
10B 10 ppm in healthy liver
10B 60 ppm in tumour liver
Skin
Soft tissue
Liver
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Advantage Depth [cm] 8.33
Advantage Depth Dose Rate [Gy-eq/min]
1.16E-3
Treatment Time [h] 143,65
Terapeutic Depth [cm] 6.13
Peak Therapeutic Ratio 3.60
In phantom figures of merit
Neutron yield = 1011 n/s
Dose limit healthy tissue: 10 Gy-eq;
TT = 10/1.16E-3 = 143.65 h
If the neutron yield is equal to 5 1012 n/s,
ADDR = 5.8 E-2 TT = 2.87 h