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

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Presentation on theme: "- April 18 th, 2005 1 Study of a DD compact neutron generator for BNCT Elisabetta Durisi Lorenzo Visca."— Presentation transcript:

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

2 - April 18 th, 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

3 - April 18 th, 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

4 - April 18 th, 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

5 - April 18 th, RF-Induction Antenna 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  3 He + n (2.45 MeV) High Voltage Shield Target Water Manifold Al 2 O 3 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

6 Turbo pumping system Roughing pump (up to mbar) Turbo pump (< mbar) HV power supply 120 kV – 300 mA HV relay Pressure gauge controllers RF power supply and matching network (freq 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.

7 - April 18 th, Installation December 2004 The compact neutron generator has been installed in the former irradiation room of the synchrotron laboratory at the Physics Institute TEST: low neutron flux, GOAL: maximum neutron flux for BNCT application, final moderator design. Al 3 O 2 insulator Vacuum pumping chamber High voltage flange and target assembly Minimum neutron yield (from agreement with LBNL) > s -1

8 - April 18 th, 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 DELIMITER Gamma shielding

9 - April 18 th, 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

10 - April 18 th, BSA with MCNP: EXAMPLE Teflon = 1 cm Al 2 O 3 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 MgF 2 Air y x Lead + Antimony Al AlF 3 y z Epithermal column: 19 cm MgF cm Al + 10 cm MgF Al + 5 air; beam exit window 20x20 cm 2 Distance: center of the source-beam exit window = 80 cm

11 - April 18 th,  epith [cm -2 s -1 ] 2.41E61.2E81E8-1E9 J epith [cm -2 s -1 ]1.46E67.3E7 D f /  epith [Gy cm 2 ] 1.87 E-12 < 2E-13 D  /  epith [Gy cm 2 ] 3.42 E-13 < 2E-13 J epith /  epith >= 0.7 Free beam parameters Recommended values for brain tumour treatment IAEA-TECDOC-1223 Neutron yield n/s- 120 kV, 300 mANeutron yield n/s-160 kV, 1 A

12 - April 18 th, Neutron spectra (Neutron yield n/s)

13 - April 18 th, In phantom figures of merit Gamma dose “D  ”, combination of the doses deriving from the beam and the photons induced by 1 H(n,  ) 2 H capture reaction with the hydrogen in tissue. Hydrogen dose “D H ” or fast neutron dose due to proton- recoil reactions at the higher neutron energies (> 1 keV) in the tissue. Thermal neutron dose “D N ”, due to the thermal neutron capture mainly by nitrogen nuclei 14 N(n,p) 14 C. Boron dose “D B ”, due to neutron capture reaction with boron. Biological dose = D W = w  D  + w n (D H + D N ) + w B D B

14 - April 18 th, Material RBE for  (w  ) RBE for n (w n ) 10 B (ppm) 10 B CBE (w B ) Skin Soft tissue Healthy liver tissue Tumour liver tissue Values used in all the simulations These are the weighting factors commonly used for brain tumour

15 - April 18 th, The Anthropomorphic phantom ADAM

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

17 - April 18 th, B 15 ppm in skin 10 B 10 ppm in healthy liver 10 B 60 ppm in tumour liver Skin Soft tissue Liver

18 - April 18 th, 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 Ratio3.60 In phantom figures of merit Neutron yield = 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-2 TT = 2.87 h

19 - April 18 th, Development of the interlock system 1. 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.

20 - April 18 th, Interlock system 1.Access doors (must be locked) 2.Area monitors (neutron and photon doses must be below fixed values) 3.Air conditioning system (10 changes per hour) 4.Locking of the moderator 5.Completion of the patrol in irradiation room and adjacent rooms 1.Stability of neutron emission rate 2.Temperature of water cooling system 3.Pressure inside the void chamber 4.Constant gas flow 5.RF generator 6.HV spikes (may damage the neutron generator) Radiation protection Neutron generator

21 - April 18 th, Development of the source monitor 1.Different types of neutron detectors 2.Position of detectors 3.Electronic chain 4.Calibration of neutron detectors

22 - April 18 th, Neutron source monitor: choice of neutron detector and position Gas detectors are universally considered the best for on-line neutron beam monitoring. BF 3 and 3 He proportional counters, compensated ion chambers, fission chambers are commonly used. 3 He: very “clear” response to neutrons, but may be more expensive with respect to BF 3 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.

23 - April 18 th, Neutron source monitor: choice of electronic chain 1.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

24 - April 18 th, Neutron source monitor: calibration of neutron detectors ASTM standard calibration procedure by IAEA IAEA-TECDOC-1223 “Current status of Neutron Capture Therapy”, 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.


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