1. Study of a DD compact neutron generator for BNCT
Elisabetta Durisi
Lorenzo Visca
April 18th, 2005

2. durisi@to.infn.it, visca@to.infn.it - April 18th, 2005
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
April 18th, 2005

3. durisi@to.infn.it, visca@to.infn.it - April 18th, 2005
Neutron Sources
Cell-killing 10B-Capture in Tumour
Neutron sources
Moderator Material
Tissue (moderator)
fast neutrons
epithermal neutrons
slow neutrons
Within patient’s body
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.
April 18th, 2005

4. Patologies treated with BNCT neutron source: REACTOR
Epithermal neutron to treat:
Brain tumour
Fir-1 Espoo Helsinki, Finland;
Massachusetts Institute of Technology;
Brookhaven National Laboratory;
Studsvik, Sweden;
High Flux Reactor Petten, Netherlands;
Head and Neck tumour
Kyoto University Reasearch Reactor, Japan
Thermal neutron to treat
Melanoma
Massachusetts Institute of Technology;
RA-6 Reactor at the Bariloche Atomic Center Buenos Aires, Argentina
Explanted Liver
Triga Mark II reactor Pavia, Italy
April 18th, 2005

5. durisi@to.infn.it, visca@to.infn.it - April 18th, 2005
DD compact neutron generator developed by LBNL - accelerator and fusion division
A 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)
45 cm
High Voltage Shield
Target Water Manifold
Al2O3 High Voltage Insulator
Target Cylinder
gas in
Secondary Electron Filter Electrode
60 cm
Ion Source
RF-Induction Antenna
RF-Induction Antenna
Vacuum Chamber
Secondary Electron Filter Electrode è alla stessa tensione del target (negativo) per schermare gli elettroni che escono dal Ti.
Il numero di ioni che arrivano sul target idealmente è = alla corrente impostata sul HV. Ma ci sono delle dispersioni (circuito di raffreddamento e elettroni secondari) quindi il numero di ioni è minore della corrente impostata. Suggerimento caratterizzazione tensione corrente della macchina.
RF-Antenna Guide
Vacuum Pump
April 18th, 2005

6. 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.
HV power supply
120 kV – 300 mA
HV relay
Turbo pumping system
Roughing pump (up to mbar)
Turbo pump (<10-10 mbar)
Pressure gauge controllers
RF power supply and matching network (freq MHz, max. transfer power 5000 W)
Deuterium gas flow system

7. durisi@to.infn.it, visca@to.infn.it - April 18th, 2005
Installation
December 2004
The compact neutron generator has been installed in the former irradiation room of the synchrotron laboratory at the Physics Institute
Al3O2 insulator
Vacuum pumping chamber
High voltage flange and target assembly
TEST:
low neutron flux,
GOAL:
maximum neutron flux for BNCT application,
final moderator design.
Minimum neutron yield (from agreement with LBNL) > 1011 s-1
April 18th, 2005

8. 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:
maintaining adequate beam flux,
minimizing undesired dose to the patient’s body and other non-tumour locations.
The major components of BSA are:
MODERATOR
REFLECTOR
DELIMITER
Gamma shielding
April 18th, 2005

9. 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
April 18th, 2005

10. BSA with MCNP: EXAMPLE y x z
Teflon= 1 cm
Al2O3
Target: Al, water cooling inside target and Fe outside
Bismuth
Extraction grid + water pipes
Copper Plasma chamber + water cooling
RF antenna: quartz outside, water inside
Lithiated polyethylene= 5 cm
MgF2
Air y x
Lead + Antimony Al
AlF3 z
Epithermal column: 19 cm MgF cm Al + 10 cm MgF2 + 5 Al + 5 air; beam exit window 20x20 cm2
Distance: center of the source-beam exit window = 80 cm
April 18th, 2005

11. Free beam parameters
Neutron yield 1011 n/s- 120 kV, 300 mA
Neutron yield n/s-160 kV, 1 A
Fepith [cm-2 s-1]
2.41E6
1.2E8
1E8-1E9
Jepith [cm-2 s-1]
1.46E6
7.3E7
Df / Fepith [Gy cm2]
1.87 E-12
< 2E-13
Dg /Fepith [Gy cm2]
3.42 E-13
Jepith/Fepith
0.607
>= 0.7
Recommended values for brain tumour treatment IAEA-TECDOC-1223
April 18th, 2005

12. Neutron spectra (Neutron yield 1011 n/s)
April 18th, 2005

13. In phantom figures of merit
Biological dose = DW = wg Dg + wn (DH + DN) + wB DB
Gamma dose “Dg”, combination of the doses deriving from the beam and the photons induced by 1H(n,g)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.
April 18th, 2005

14. Values used in all the simulations
Material
RBE for g (wg)
RBE for n (wn)
10B (ppm)
10B CBE (wB)
Skin 1
3.2 15
2.5
Soft tissue 10
Healthy liver tissue
1.3
Tumour liver tissue 60
3.8
Values used in all the simulations
These are the weighting factors commonly used for brain tumour
April 18th, 2005

15. The Anthropomorphic phantom ADAM
April 18th, 2005

16. BSA with MCNP: EXAMPLE x y Liver segmentation
ICRU reference phantom
implemented in MCNP by ENEA – Bologna
SPINE
KIDNEYS
PANCREAS
SPLEEN
STOMACH
ARM BONES
RIB CAGE SURFACE
BLADDER x
SKIN ON TRUNK
Liver segmentation y
Cross section of the Anthropomorphic phantom ADAM
April 18th, 2005

17. durisi@to.infn.it, visca@to.infn.it - April 18th, 2005
10B 15 ppm in skin
10B 10 ppm in healthy liver
10B 60 ppm in tumour liver
Skin
Soft tissue
Liver
April 18th, 2005

18. In phantom figures of merit
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
Neutron yield = 1011 n/s
Dose limit healthy tissue: 10 Gy-eq;
TT = 10/1.16E-3 = h
If the neutron yield is equal to n/s,
ADDR = 5.8 E TT = 2.87 h
April 18th, 2005

19. Development of the interlock system
Radiation protection interlock system
to avoid excessive doses to exposed workers and general public.
2. Neutron generator interlock system
to avoid damage to the neutron generator and allow operation under safe conditions.
Certified systems must be employed.
April 18th, 2005

20. durisi@to.infn.it, visca@to.infn.it - April 18th, 2005
Interlock system
Radiation protection
Neutron generator
Access doors (must be locked)
Area monitors (neutron and photon doses must be below fixed values)
Air conditioning system (10 changes per hour)
Locking of the moderator
Completion of the patrol in irradiation room and adjacent rooms
Stability of neutron emission rate
Temperature of water cooling system
Pressure inside the void chamber
Constant gas flow
RF generator
HV spikes (may damage the neutron generator)
April 18th, 2005

21. Development of the source monitor
Different types of neutron detectors
Position of detectors
Electronic chain
Calibration of neutron detectors
April 18th, 2005

22. Neutron source monitor: choice of neutron detector and position
Gas detectors are universally considered the best for on-line neutron beam monitoring.
BF3 and 3He proportional counters, compensated ion chambers, fission chambers are commonly used.
3He: very “clear” response to neutrons, but may be more expensive with respect to BF3 tubes.
Ion chambers: may be useful for high fluxes.
Fission chambers: very reliable, but longer procedures for authorizations.
Position of detectors: inside the moderator; criteria of convenience determine the allocation.
April 18th, 2005

23. Neutron source monitor: choice of electronic chain
Charge modality (the single pulse is counted)
Electronic chain: preamplifier, amplifier, SCA, PC
2. Current modality
Electronic chain: preamplifier, ammeter, PC
Greater precision
Better discrimination between neutron signal and gamma/electronic signal
Much higher fluxes can be measured
It is possible to “compensate” for the electronic noise and gamma signal
April 18th, 2005

24. Neutron source monitor: calibration of neutron detectors
ASTM standard calibration procedure by IAEA
IAEA-TECDOC-1223 “Current status of Neutron Capture Therapy”, 2001
1. Activation foils, whose responses are known, are exposed simultaneously to detectors. The position of detectors is fixed. Detector response is recorded.
2. Activation of foils is measured; results are unfolded with a suitable unfolding code, thus obtaining a neutron spectrum of the source.
3. The calibration factor can be obtained, by taking into account the geometry of the system and by comparison between the on-line response of the detectors and the unfolded spectrum.
April 18th, 2005