Compact Sealed lithium target for accelerator-driven BNCT system 6th High Power Targetry Workshop （11 – 15 April 2016, Merton College Oxford） Compact Sealed lithium target for accelerator-driven BNCT system Kazuki Tsuchida and Yoshiaki Kiyanagi Nagoya University ｐ1

What is BNCT ( Boron Neutron Capture Therapy )? Cancer cells in the affected area could be killed individually by irradiating neutrons to the 10B accumulated in the cancer cells, because an alpha particle and a 7Li nucleus produced by a 10B fission process would travel less than the size of a cell. BNCT clinical application was started by using a nuclear reactor in BNL (Sweet et al. ) and also MIT in 1950’s. Dr. Hatanaka successfully applied BNCT to brain malignant glioma in 1974 and some Japanese medical doctors continued basic research and clinical applications of BNCT by using nuclear reactors. Cancer cell 10B + n → 7Li + α + 2.38MeV 10B n 7Li α Normal cell Thermal neutrons Particle range 4μm　　9μm 　　　　　　　　　( < Cell size ～10μm ) To establish the BNCT as one of cancer treatments in the hospital, it is needed to develop accelerator-driven neutron sources, taking over the nuclear reactor-based one. Dr. Locker presented the basic idea of the BNCT in 1936, 4 years after Chadwick discovered the neutron. However, BNL and MIT trials were failed due to the low accumulation of boron compound and improper characteristics of neutron beam.

Two BNCT facilities are in the clinical trial phase and Four BNCT facilities are under construction in Japan. Cyclotron & Be target Minami Tohoku Hospital （ Clinical trial 2016 ～ ） Linac & Be target Tsukuba Univ. （ Under commissioning ） Osaka Medical Univ. （ Under construction ） Linac & Li target Kyoto Univ. (kumatori) （ Clinical trial 2013 ～ ） National Cancer Center （Const. completed） Okinawa （ Planning ） Edogawa Hospital （ Construction 2017～） DC Acc. & Li target Osaka Univ. ( Planning ） Nagoya Univ. （ Under commissioning ）

Accelerator-driven neutron source for BNCT proton Fast neutron Epi thermal neutron Accelerator Target Beam Shaping Assembly Treatment region Proton 2 – 30 MeV 40 – 80 kW Li, Be Specifications of the BNCT system for clinical application Sufficient flux and good quality of epi thermal neutron beam (IAEA TECDOC* ) Epi thermal neutron flux Nepi > 1 x 109 n/cm2 s ( En : 0.5 eV -10 keV ) Contamination of fast neutron Df ≦2×10-13 Gy・cm2 Contamination of thermal neutron and γ-ray, Current / flux ratio (2) Reduction radiation exposure to medical and maintenance staffs (3) Low activation of accelerator and facility (4) Safe and good reliability as a medical equipment (5) Easy and quick maintenance (6) Low construction and running costs 原子炉に代わる新たな中性子源として加速器を利用するという試みがある 加速器を用いた中性子源としてこの４つが主にあげられる。 ４つを読まない 町中の病院施設の併設可能性 加速粒子を金属ターゲットに当てて、その際生じる核反応を利用する これまで検討されてきた反応としてこれらがあげられる * IAEA-TECDOC-1223 ”Current states of neutron capture therapy”, IAEA (2001).

Many types of accelerator-driven neutron system are developed or developing in Japan. The 2nd and 3rd system will be operated for BNCT application in a few years.

Neutron spectrum of neutrons Spatially-varied neutron spectrum in the BSA 2m H+ 30MeV Be target Epithermal region Li target H+ 2.8MeV 1.2m Neutron spectrum of neutrons in the BSA (Lethargy)

Development of a sealed Li target for BNCT application A compact sealed lithium target is under development for BNCT application and it’s applicability will be confirmed in combination with a Dynamitron. mA). Compact & Sealed Li target 15mA

Cross sectional view of the Compact Sealed Li target Completed Ta backing plate is connected to a Cu cooling base by HIP process*. The emboss-structure is prepared on the surface of Ta plate. Ta : High threshold for blistering ( H+ fluence > 1.6 x 1021 H+/cm2 ) High corrosion resistance and good wettability for liquid Lithium (2) Thin Ti foil is jointed to the Ta plate by Hot press process. Ti : High corrosion resistance and good wettability for liquid Lithium (3) Li is set in the thin space of the emboss structure. ← Under development (4) Proton beam is irradiate to the Li through the Ti foil. Li and Be-7 can be confined in the target by the Ti foil. Proton Beam ( >2.8MeV, 42kW ) Power density : 6.6 MW / m2 ( Irradiation area = 80 x 80 mm2) こんなターゲットつかうよ的な説明 一番問題は熱除去なので、充填方法や接合方法は後回し エンボスの説明いらない。 Ti or Be foil ( t ～ 10 μm ) Li layer ( t ～ 0.14mm ) Cooling water Cu base (130 x 130 mm) Ta backing plate ( *HIP : Hot Isostatic Press )

Heat transfer improvement by a turbulent water flow V-staggered rib Parallel rib Water flow Water flow Proton Beam Proton Beam Water flow Water flow This drawing is indicated by turn upside down. RANS (Reynolds-averaged Navier–Stokes) analysis

Temperature analysis of the Li target - Input data - The energy deposition of the 2.8MeV proton in each layers of the Li target can be calculated by the SRIM code. Ti Li Ta (1) Ti layer : 0.34 MeV (2) Li layer : 1.07 MeV (3) Ta layer : 1.39 MeV ( In the penetration depth of10 µm ) Proton 2.8 MeV,15 mA on the 80x80 （ ㎝2 ） Ti foil Li layer Ta layer Water Cu plate Heat conduction rate h = 1.1×105 [W/m2/K] Water temperature = 20 ℃

Temperature analysis of the Li target Maximum temperature of the Li target surface is calculated to be143℃, when the proton beam of 42 kW is irradiated on the area of 8 x 8 cm2 ⇒　We could solved the issue of the heat removable form the Li target. Temperature [ K ]　 その時の平衡時の温度シミュレーション結果がこちらです。 詳細な温度推定を行う予定 さらに面積を減らした場合でもいけるかも もともと中性子を発生させるためのターゲットなので、照射面積が小さい方が中性子が拡散せず、患部に集中的に照射が可能である。そのため、もともと照射面積80mm×80mmの予定であったが、より狭い照射面積でも、温度上昇は抑えることが可能なので、シミュレーションを行った。 実際には、Ti-Ta間、Ta-Cu間の接合部に熱抵抗が発生し、これより温度は高くなる 今後、Ta、Tiを含むターゲットにて同様の熱付加試験を行う必要がある 6.5625kWの時159℃まで温度が上昇

Strengthened metallic foil for the Sealed Li target (1) For BNCT medical application, Li and Be-7 should be confined in the target by a secure metallic foil during the target life (> 160 hours), which is limited by the damage of Ta backing plate due to the blistering. (2) To improve the strength of the metallic foil, we developed a titanium alloy foil (10μm).　 　　Titanium Alloy-1 　　　 Ti – Al (0.5) – Si (0.4) (mass%) (3) This has high strength (3 times higher than pure titanium at 400℃）, good oxidation resistance and good formability ( same as pure titanium).

Concept of BNCT with gantry system By developing a confined Li target, compact BNCT system with a gantry would be realized and patients could be treated under a prevention of stress by the advanced BNCT system. Target & Moderator System Size Φ1.2m x L1m Weight ～6 tons H+ Neutron Gantry system Treatment table This concept was proposed by IBA (Appl. Rad. Isotopes. 67 (2009) S262

Member of Nagoya BNCT Project K. Tsuchida1, Y. Kiyanagi1 Y. Menjo2,Furuzawa2, A. Uritani2, K. Watanabe2, Yamazaki2, Tsuji2, Tsuneyoshi2 H. M. Shimizu3, K. Hirota3, M. Kitaguchi3, G. Ichikawa3, F. Hiraga4 (Nagoya University) 1 Accelerator-based BNCT system, Graduate School of Engineering 2 Materials, Physics and Energy Engineering, Graduate School of Engineering 3 Department of Physics, Graduate School of Science (Hokkaido University) 4 Quantum Science and Engineering, Graduate School of Engineering

Thank you for your attention!! Trill (11 years)