Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Project for the development of the linac based NCT facility in University of Tsukuba H. Kumada a,n, A. Matsumura b, H. Sakurai a, T. Sakae a, M. Yoshioka c, H. Kobayashi c, H. Matsumoto c, Y. Kiyanagi d, T. Shibata e, H. Nakashima e a
Proton Medical Research Centre, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan Department of Neurosurgery, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan c High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan d Laboratory of Quantum Beam System, Hokkaido University, Sapporo, Hokkaido 060-0808, Japan e J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan b
H I G H L I G H T S
A project team headed by University of Tsukuba launched a development of new accelerator based BNCT facility. The project adopted an 8 MeV RFQ þDTL type linac as proton accelerator. The linac tube is completed and installed in BNCT facility at Tokai village. Neutron generator device with beryllium target is being also designed and several medical devices as treatment planning system, patient positioning device are being also developed. We are now developing a new multi-modal Monte-Carlo treatment planning system based on JCDS.
art ic l e i nf o
Keywords: Accelerator based neutron source Accelerator based BNCT Linac Beryllium target Treatment planning system
a b s t r a c t A project team headed by University of Tsukuba launched the development of a new accelerator based BNCT facility. In the project, we have adopted Radio-Frequency Quadrupole (RFQ) þDrift Tube Linac (DTL) type linac as proton accelerators. Proton energy generated from the linac was set to 8 MeV and average current was 10 mA. The linac tube has been constructed by Mitsubishi Heavy Industry Co. For neutron generator device, beryllium is selected as neutron target material; high intensity neutrons are generated by the reaction with beryllium and the 80 kW proton beam. Our team chose beryllium as the neutron target material. At present beryllium target system is being designed with Monte-Carlo estimations and heat analysis with ANSYS. The neutron generator consists of moderator, collimator and shielding. It is being designed together with the beryllium target system. We also acquired a building in Tokai village; the building has been renovated for use as BNCT treatment facility. It is noteworthy that the linac tube had been installed in the facility in September 2012. In BNCT procedure, several medical devices are required for BNCT treatment such as treatment planning system, patient positioning device and radiation monitors. Thus these are being developed together with the linac based neutron source. For treatment planning system, we are now developing a new multi-modal Monte-Carlo treatment planning system based on JCDS. The system allows us to perform dose estimation for BNCT as well as particle radiotherapy and X-ray therapy. And the patient positioning device can navigate a patient to irradiation position quickly and properly. Furthermore the device is able to monitor movement of the patient's position during irradiation. & 2014 Elsevier Ltd. All rights reserved.
1. Introduction
n
Corresponding author. Tel.: þ 81 29 853 7100; fax: þ81 28 853 7102. E-mail addresses: [email protected], [email protected] (H. Kumada).
Boron Neutron Capture Therapy (BNCT) is the next-generation particle radiotherapy against intractable cancer. At present, clinical trials of BNCT are being performed using a research reactor. Clinical trials for malignant brain tumor are being conducted by a clinical team of University of Tsukuba. They have been also using a research reactor
http://dx.doi.org/10.1016/j.apradiso.2014.02.018 0969-8043 & 2014 Elsevier Ltd. All rights reserved.
Please cite this article as: Kumada, H., et al., Project for the development of the linac based NCT facility in University of Tsukuba. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.02.018i
H. Kumada et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
“JRR-4” in Japan Atomic Energy Agency (JAEA) since 1999. The results obtained from the trials proved the effectiveness of BNCT for the intractable cancer. However, the therapy is not widespread due to the need for nuclear reactor, although the effectiveness has been demonstrated. In fact, it is impossible to build a new reactor in the near future due to recent environmental concern about nuclear activities in Japan. Meanwhile recent progress in technology for neutron source with accelerator makes it possible to be used for BNCT treatment at a hospital. With this situation in mind, we launched a project for the development of accelerator based BNCT treatment in order to establish and spread the BNCT procedure both domestically and internationally. To accomplish the goal, we have set up an industry–academia– government collaboration team of University of Tsukuba, High Energy Accelerator Research Organization (KEK), JAEA, Hokkaido University, Ibaraki prefecture and Mitsubishi heavy industry Co. (MHI). The team had launched an R&D project in 2010 with many companies and research institutes. At present, the collaboration team is developing an accelerator based neutron source device applicable to BNCT. The team has been developing not only an accelerator based neutron source device but also a new medical equipment required for the BNCT procedure such as treatment planning system, patient setting device and several monitors. In this paper we would like to introduce current status of the development for the accelerator based BNCT device and medical equipment.
For case (a), it is possible that direct production of lower energy neutrons focuses on the target in principle. But we are now concerned about the management and handling of a lithium target. It has not been completely resolved for practical use outside of research facilities. In particular, we thought that it is difficult to keep radiation and activation levels of lithium target (Beryllium-7) sufficiently low to operate the treatment device in hospital. On the other hand, for case (b), a group at Kyoto University has provided a facility in collaboration with Sumitomo Heavy Industries, Ltd. (Tanaka et al., 2011). Case (c) is an ideal approach (Ceballos et al., 2011). However to realize the neutron source for BNCT by this methodology, it is required to develop not only a higher current proton accelerator but also a tough beryllium target system which can resist the heat load caused by the huge proton incident. The case (d) approach also allows us to generate neutrons by using a compact accelerator device (Capoulat et al., 2011). However we have not chosen to apply the neutron source with fusion reaction by involving tritium as an emission of radioactivity. In response to this situation, we investigated specifications of accelerator based neutron source for BNCT. As a result, an optimum target material was selected, and specifications of proton beam and proton accelerator were decided.
3. Results and discussions
2. Materials and methods
3.1. Determination of proton beam specification and target material
2.1. Concept of Tsukuba's accelerator based BNCT device
Our technology choice differs from the lithium target system and the Kyoto–Sumitomo group system. First, we have selected beryllium as neutron target material because beryllium has many advantages compared with lithium described above. Especially, beryllium has been demonstrated for its practicality and stability for neutron source of BNCT by the Kyoto–Sumitomo group. Next, specification of proton beam was decided. It needs to generate enough neutrons with beryllium. And to reduce activation for beryllium target and other several materials of the neutron generator device, we decided to decrease drastically the proton energy to much less than 30 MeV. On the other hand, in the case that the proton energy is lower than 8 MeV, the proton beam is required to irradiate higher current and power to beryllium in order to generate enough neutron intensity. Furthermore in this case, thinner beryllium plate must be applied because the depth of Bragg peak in beryllium is less than 0.5 mm. We thought that it is difficult to resist the huge heat load by using the thinner beryllium. From results of several investigations and analyses, proton energy of our neutron source was set to 8 MeV. And to achieve the goals of epithermal neutron flux (4109 n/cm2/s) with an 8 MeV proton beam and beryllium, the average proton current was set to 10 mA. Thus the maximum proton power irradiated to the beryllium target is 80 kW.
To achieve the accelerator based BNCT treatment in hospital, strategic goals and our development concept have been established as follows. (a) to produce a high flux of epithermal neutrons of more than 109 n/cm2/s at beam port; (b) to keep radiation and activation of components as low as possible; (c) to lower the production rate of fast neutrons to reduce the needed shielding materials; (d) to lower the production rate of gamma rays to reduce incidental dose of a healthy tissue. These factors are essential so that the facility could be provided in a hospital. For contamination of fast neutrons and gamma rays in the beam as in factors (c) and (d), specific target levels use international recommendations on IAEA-TECDOC (IAEA, 2001) as a benchmark. 2.2. Technology choice for accelerator and target material Technology choice for the accelerator should be based on a feasible study of the target system. Several combinations of accelerators and target materials have been proposed to realize accelerator based BNCT. Typical combinations can be classified into some groups as follows: (a) low energy ( o3 MeV), high current proton with a lithium target; (b) 30 MeV, a high energy and low current proton with a beryllium target; (c) 4–5 MeV, a low energy and high current proton with a beryllium target; (d) 1.0–1.5 MeV, a low energy bean and a beryllium target with 9 Be(d,n)10B reaction.
3.2. Development of proton accelerator and beryllium target system To generate the high current proton beam, we have chosen RFQ and a DTL type linac as the proton accelerator. The RFQ and the DTL are applied technologies of front-end Linac of “J-PARC” as a multi-purpose and multidisciplinary facility with a high-intensity proton accelerator device. J-PARC has already sufficient performance for continuous operation. A schematic drawing of the linac based BNCT device is shown in Fig. 1. Length of the linac is about 8 m and diameter is less than 1.5 m. Output energy from the RFQ is 3 MeV and the further energy gain from the DTL is 5 MeV. Specifications of the linac are shown in Table 1. The linac was
Please cite this article as: Kumada, H., et al., Project for the development of the linac based NCT facility in University of Tsukuba. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.02.018i
H. Kumada et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Neutron Generator
3
Fast neutron filter Moderator Collimator
Moderator Collimator Beryllium Target System
Beryllium target
Beam port
Patient Proton Beam
Neutron
Shield
Proton beam
RFQ+DTL Type Proton Linac
Thermal neutron filer and gamma-ray filer
Fig. 1. Scheme of linac based BNCT device.
Shielding Table 1 Specifications of the linac.
Fig. 2. Scheme of neutron generator with beryllium target.
Accelerator Type
RFQþ DTL type linac
Proton energy Peak current Average current Beam width Beam duty Power to target Dimension
8 MeV 50 mA 45 mA (max. 10 mA) 1 ms 20% 440 kW (max. 80 kW) Length: o 7 m, footprint: o 50 m2
designed mainly by KEK and MHI has taken the production of the linac. Both tubes of RFQ and DTL had been completed in 2012. Second key technology for achievement of the project is development of the neutron target device with beryllium. Depth of Bragg peak of 8 MeV proton energy is less than 1 mm. Thus the thickness of beryllium is set as 0.5 mm, and the copper plate as a heat sink is located at the backside of the beryllium plate. And to avoid blistering caused by the high current proton incidence, an intermediate material is installed between the beryllium plate and the copper heat sink. The three materials are bonded by a Hot Isostatic Pressing (HIP) method. Primary development subject for the neutron target device with the thin beryllium plate is removal of heat that is generated by irradiation of up to 80 kW proton power. At present, we are designing the beryllium target system using both Monte-Carlo analysis and ANSYS as heat analysis tools. In addition we have prepared a Cockcroft type proton injector in order to perform experiments of proton irradiation with the target system. And we are also investigating to select a suitable intermediate material. Based on the results of the experiments, some prototypes of the beryllium target system will be produced in 2013. 3.3. Design of neutron generator device with beryllium target At present, the project team is designing not only beryllium target system but also moderator, collimator and radiation shield to form the neutron generator device. To determine conceptual design of the device, Monte-Carlo analysis using PHITS as a multi-purpose MonteCarlo code is being performed (Iwase et al., 2002). Fig. 2 shows a schematic cross-section view of the neutron generator device. Epithermal neutron flux, contaminations of fast neutron dose and gamma-ray dose at beam port were determined by the Monte-Carlo estimation while changing the parameters of material, dimensions and shape of each element. The results of the Monte-Carlo analysis demonstrated that a neutron generator model with 80 kW proton beam irradiation can generate enough epithermal neutron flux (42.0 109 n/cm2/s) at the beam port. We are performing the estimation continuously and basic design of proper neutron generator had been determined at the end of 2012. First, high energy neutrons generated at beryllium target are reduced by a fast neutron filter made of iron. And a moderator is installed behind the fast neutron filter in order to create epithermal neutrons. To reduce gamma-rays and to cut thermal neutrons in the
Fig. 3. RFQ and DLT tubes installed in the accelerator room in iNMRC.
Irradiation Ion Source
Room Patient
Neutron Generator
RFQ
DTL
Proton Beam
Accelerator Room Fig. 4. Cross section view of Tsukuba's BNCT facility in the iNMRC.
beam, bismuth filter and cadmium filter are located at the back of the moderator. Finally the epithermal neutrons are focused to beam aperture by the collimator made of polyethylene and lead. 3.4. Treatment facility To conduct actual treatment using the linac based neutron source in the near future, our team has acquired a suitable building. It is a building which is managed by Ibaraki prefecture; it is located near JAEA in Tokai village. The building has been renovated by Ibaraki Prefecture. It can house the linac-based neutron source, and can also accept high intensity neutrons in an irradiation room. The building has
Please cite this article as: Kumada, H., et al., Project for the development of the linac based NCT facility in University of Tsukuba. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.02.018i
H. Kumada et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
Fig. 5. Screen shot of treatment planning with Tsukuba plan.
been completed as BNCT facility, and it was named “Ibaraki Neutron Medical Research Center” (abbreviated as, “iNMRC”) in December 2012. Both the tubes of RFQ and DTL as shown in Fig. 3 were installed in an accelerator room in iNMRC in September 2012. Fig. 4 shows layout of each device in the building. The neutron generator device was installed to a prescribed position in the irradiation room in 2013. Proton beam emitted from the linac at the neighbor room reaches the irradiation room through a separation wall and the proton beam bends, and finally the protons generate high intensity neutrons by the reaction with beryllium.
University were applied. The monitored data of patient's position by the device will be utilized for irradiation management as well as for quality assurance and quality control (QA/QC) of the therapy. Furthermore we intend to develop Prompt Gamma-ray SPECT (PG-SPECT) which can estimate directly the boron dose distribution as well as the change in boron concentration around target region during irradiation. At present, we are developing a prototype of PG-SPECT system and scintillators were applied to gammaray detector of the system.
3.5. Development of a medical equipment
4. Conclusions
For the development of a treatment planning system, a new Monte-Carlo based system (developing code; Tsukuba Plan) is under development based on fundamental technologies of JCDS (Kumada et al., 2007). JCDS has actual achievements and reliability based on application to treatment planning of clinical trials performed at JRR-4. To improve dosimetry performance of Tsukuba plan, original MontelCarlo transport engine is being developed with PHITS technologies. The Monte-Carlo transport engine can calculate behavior of neutron and photon as well as proton and heavy ions. Thus the Tsukuba Plan enables us to perform dose estimation of not only BNCT but also particle radiotherapy and X-ray therapy. And the system allows estimating total dose of combined radiotherapy. Fig. 5 shows a working view of Tsukuba Plan. A new patient positioning device is being developed together with Tsukuba Plan. The device navigates a patient to irradiation position quickly. Alignment method of the device is the employed methodology of JRR-40 s patient setting system (Kumada et al., 2000). Furthermore the device has the function of monitoring the patient's movement in real-time during irradiation. In the development of the monitoring method, fundamental technologies of real-time tracking proton radiotherapy developed in Tsukuba
The project team consisting of specialists of several research institutes headed by University of Tsukuba has launched the development of an accelerator based BNCT facility. At present 8 MeV energy proton linac is being produced. The linac tube has been completed and installed in iNMRC. Neutron generator device with a beryllium target system is being designed. The neutron generator has been constructed and installed to the irradiation room at iNMRC in 2013. The neutron generator combined with the linac will generate adequate epithermal neutrons for BNCT in 2014. Several medical devices such as treatment planning system, patient positioning device and radiation monitors will be completed by 2014. In the current schedule, a first clinical trial using the linac-based BNCT facility is planned to be performed in 2015. References Capoulat, M.E., Minsky, D.M., Kreiner, A.J., 2011. Application of the 9Be(d,n)10B reaction to AB-BNCT skin and deep tumor treatment. Appl. Radiat. Isot. 69, 1684–1687. Ceballos, C., Esposito, J., Agosteo, S., et al., 2011. Towards the final BSA modeling for the accelerator-driven BNCT facility at INFN LNL. Appl. Radiat. Isot. 69, 1660–1663.
Please cite this article as: Kumada, H., et al., Project for the development of the linac based NCT facility in University of Tsukuba. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.02.018i
H. Kumada et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎ International Atomic Energy Agency, 2001. Current status of neutron capture therapy. International Atomic Energy Agency (IAEA-TECDOC-1223) Iwase, H., Niita, K., Nakamura, T., 2002. Development of general-purpose particle and heavy ion transport Monte Carlo code. J. Nucl. Sci. Technol. 39, 1142–1151. Kumada, H. Yamamoto, K., et al., Development of the patient setting system for BNCT at JRR-4: program & abstracts, In: Proceedings of the 9th International Symposium on Neutron Capture Therapy for Cancer, 2000, p. 281.
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Kumada, H., et al., 2007. Development of JCDS, a computational dosimetry system at JAEA for boron neutron capture therapy. J. Phys. Conf. 74, 1–7. Tanaka, H., Sakurai, Y., Suzuki, M., et al., 2011. Experimental verification of beam characteristics for cyclotron-based epithermal neutron source (C-BENS). Appl. Radiat. Isot. 69, 1642–1645.
Please cite this article as: Kumada, H., et al., Project for the development of the linac based NCT facility in University of Tsukuba. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.02.018i
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Project for the development of the linac based NCT facility in University of Tsukuba H. Kumada a,n, A. Matsumura b, H. Sakurai a, T. Sakae a, M. Yoshioka c, H. Kobayashi c, H. Matsumoto c, Y. Kiyanagi d, T. Shibata e, H. Nakashima e a
Proton Medical Research Centre, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan Department of Neurosurgery, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan c High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan d Laboratory of Quantum Beam System, Hokkaido University, Sapporo, Hokkaido 060-0808, Japan e J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan b
H I G H L I G H T S
A project team headed by University of Tsukuba launched a development of new accelerator based BNCT facility. The project adopted an 8 MeV RFQ þDTL type linac as proton accelerator. The linac tube is completed and installed in BNCT facility at Tokai village. Neutron generator device with beryllium target is being also designed and several medical devices as treatment planning system, patient positioning device are being also developed. We are now developing a new multi-modal Monte-Carlo treatment planning system based on JCDS.
art ic l e i nf o
Keywords: Accelerator based neutron source Accelerator based BNCT Linac Beryllium target Treatment planning system
a b s t r a c t A project team headed by University of Tsukuba launched the development of a new accelerator based BNCT facility. In the project, we have adopted Radio-Frequency Quadrupole (RFQ) þDrift Tube Linac (DTL) type linac as proton accelerators. Proton energy generated from the linac was set to 8 MeV and average current was 10 mA. The linac tube has been constructed by Mitsubishi Heavy Industry Co. For neutron generator device, beryllium is selected as neutron target material; high intensity neutrons are generated by the reaction with beryllium and the 80 kW proton beam. Our team chose beryllium as the neutron target material. At present beryllium target system is being designed with Monte-Carlo estimations and heat analysis with ANSYS. The neutron generator consists of moderator, collimator and shielding. It is being designed together with the beryllium target system. We also acquired a building in Tokai village; the building has been renovated for use as BNCT treatment facility. It is noteworthy that the linac tube had been installed in the facility in September 2012. In BNCT procedure, several medical devices are required for BNCT treatment such as treatment planning system, patient positioning device and radiation monitors. Thus these are being developed together with the linac based neutron source. For treatment planning system, we are now developing a new multi-modal Monte-Carlo treatment planning system based on JCDS. The system allows us to perform dose estimation for BNCT as well as particle radiotherapy and X-ray therapy. And the patient positioning device can navigate a patient to irradiation position quickly and properly. Furthermore the device is able to monitor movement of the patient's position during irradiation. & 2014 Elsevier Ltd. All rights reserved.
1. Introduction
n
Corresponding author. Tel.: þ 81 29 853 7100; fax: þ81 28 853 7102. E-mail addresses: [email protected], [email protected] (H. Kumada).
Boron Neutron Capture Therapy (BNCT) is the next-generation particle radiotherapy against intractable cancer. At present, clinical trials of BNCT are being performed using a research reactor. Clinical trials for malignant brain tumor are being conducted by a clinical team of University of Tsukuba. They have been also using a research reactor
http://dx.doi.org/10.1016/j.apradiso.2014.02.018 0969-8043 & 2014 Elsevier Ltd. All rights reserved.
Please cite this article as: Kumada, H., et al., Project for the development of the linac based NCT facility in University of Tsukuba. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.02.018i
H. Kumada et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
“JRR-4” in Japan Atomic Energy Agency (JAEA) since 1999. The results obtained from the trials proved the effectiveness of BNCT for the intractable cancer. However, the therapy is not widespread due to the need for nuclear reactor, although the effectiveness has been demonstrated. In fact, it is impossible to build a new reactor in the near future due to recent environmental concern about nuclear activities in Japan. Meanwhile recent progress in technology for neutron source with accelerator makes it possible to be used for BNCT treatment at a hospital. With this situation in mind, we launched a project for the development of accelerator based BNCT treatment in order to establish and spread the BNCT procedure both domestically and internationally. To accomplish the goal, we have set up an industry–academia– government collaboration team of University of Tsukuba, High Energy Accelerator Research Organization (KEK), JAEA, Hokkaido University, Ibaraki prefecture and Mitsubishi heavy industry Co. (MHI). The team had launched an R&D project in 2010 with many companies and research institutes. At present, the collaboration team is developing an accelerator based neutron source device applicable to BNCT. The team has been developing not only an accelerator based neutron source device but also a new medical equipment required for the BNCT procedure such as treatment planning system, patient setting device and several monitors. In this paper we would like to introduce current status of the development for the accelerator based BNCT device and medical equipment.
For case (a), it is possible that direct production of lower energy neutrons focuses on the target in principle. But we are now concerned about the management and handling of a lithium target. It has not been completely resolved for practical use outside of research facilities. In particular, we thought that it is difficult to keep radiation and activation levels of lithium target (Beryllium-7) sufficiently low to operate the treatment device in hospital. On the other hand, for case (b), a group at Kyoto University has provided a facility in collaboration with Sumitomo Heavy Industries, Ltd. (Tanaka et al., 2011). Case (c) is an ideal approach (Ceballos et al., 2011). However to realize the neutron source for BNCT by this methodology, it is required to develop not only a higher current proton accelerator but also a tough beryllium target system which can resist the heat load caused by the huge proton incident. The case (d) approach also allows us to generate neutrons by using a compact accelerator device (Capoulat et al., 2011). However we have not chosen to apply the neutron source with fusion reaction by involving tritium as an emission of radioactivity. In response to this situation, we investigated specifications of accelerator based neutron source for BNCT. As a result, an optimum target material was selected, and specifications of proton beam and proton accelerator were decided.
3. Results and discussions
2. Materials and methods
3.1. Determination of proton beam specification and target material
2.1. Concept of Tsukuba's accelerator based BNCT device
Our technology choice differs from the lithium target system and the Kyoto–Sumitomo group system. First, we have selected beryllium as neutron target material because beryllium has many advantages compared with lithium described above. Especially, beryllium has been demonstrated for its practicality and stability for neutron source of BNCT by the Kyoto–Sumitomo group. Next, specification of proton beam was decided. It needs to generate enough neutrons with beryllium. And to reduce activation for beryllium target and other several materials of the neutron generator device, we decided to decrease drastically the proton energy to much less than 30 MeV. On the other hand, in the case that the proton energy is lower than 8 MeV, the proton beam is required to irradiate higher current and power to beryllium in order to generate enough neutron intensity. Furthermore in this case, thinner beryllium plate must be applied because the depth of Bragg peak in beryllium is less than 0.5 mm. We thought that it is difficult to resist the huge heat load by using the thinner beryllium. From results of several investigations and analyses, proton energy of our neutron source was set to 8 MeV. And to achieve the goals of epithermal neutron flux (4109 n/cm2/s) with an 8 MeV proton beam and beryllium, the average proton current was set to 10 mA. Thus the maximum proton power irradiated to the beryllium target is 80 kW.
To achieve the accelerator based BNCT treatment in hospital, strategic goals and our development concept have been established as follows. (a) to produce a high flux of epithermal neutrons of more than 109 n/cm2/s at beam port; (b) to keep radiation and activation of components as low as possible; (c) to lower the production rate of fast neutrons to reduce the needed shielding materials; (d) to lower the production rate of gamma rays to reduce incidental dose of a healthy tissue. These factors are essential so that the facility could be provided in a hospital. For contamination of fast neutrons and gamma rays in the beam as in factors (c) and (d), specific target levels use international recommendations on IAEA-TECDOC (IAEA, 2001) as a benchmark. 2.2. Technology choice for accelerator and target material Technology choice for the accelerator should be based on a feasible study of the target system. Several combinations of accelerators and target materials have been proposed to realize accelerator based BNCT. Typical combinations can be classified into some groups as follows: (a) low energy ( o3 MeV), high current proton with a lithium target; (b) 30 MeV, a high energy and low current proton with a beryllium target; (c) 4–5 MeV, a low energy and high current proton with a beryllium target; (d) 1.0–1.5 MeV, a low energy bean and a beryllium target with 9 Be(d,n)10B reaction.
3.2. Development of proton accelerator and beryllium target system To generate the high current proton beam, we have chosen RFQ and a DTL type linac as the proton accelerator. The RFQ and the DTL are applied technologies of front-end Linac of “J-PARC” as a multi-purpose and multidisciplinary facility with a high-intensity proton accelerator device. J-PARC has already sufficient performance for continuous operation. A schematic drawing of the linac based BNCT device is shown in Fig. 1. Length of the linac is about 8 m and diameter is less than 1.5 m. Output energy from the RFQ is 3 MeV and the further energy gain from the DTL is 5 MeV. Specifications of the linac are shown in Table 1. The linac was
Please cite this article as: Kumada, H., et al., Project for the development of the linac based NCT facility in University of Tsukuba. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.02.018i
H. Kumada et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Neutron Generator
3
Fast neutron filter Moderator Collimator
Moderator Collimator Beryllium Target System
Beryllium target
Beam port
Patient Proton Beam
Neutron
Shield
Proton beam
RFQ+DTL Type Proton Linac
Thermal neutron filer and gamma-ray filer
Fig. 1. Scheme of linac based BNCT device.
Shielding Table 1 Specifications of the linac.
Fig. 2. Scheme of neutron generator with beryllium target.
Accelerator Type
RFQþ DTL type linac
Proton energy Peak current Average current Beam width Beam duty Power to target Dimension
8 MeV 50 mA 45 mA (max. 10 mA) 1 ms 20% 440 kW (max. 80 kW) Length: o 7 m, footprint: o 50 m2
designed mainly by KEK and MHI has taken the production of the linac. Both tubes of RFQ and DTL had been completed in 2012. Second key technology for achievement of the project is development of the neutron target device with beryllium. Depth of Bragg peak of 8 MeV proton energy is less than 1 mm. Thus the thickness of beryllium is set as 0.5 mm, and the copper plate as a heat sink is located at the backside of the beryllium plate. And to avoid blistering caused by the high current proton incidence, an intermediate material is installed between the beryllium plate and the copper heat sink. The three materials are bonded by a Hot Isostatic Pressing (HIP) method. Primary development subject for the neutron target device with the thin beryllium plate is removal of heat that is generated by irradiation of up to 80 kW proton power. At present, we are designing the beryllium target system using both Monte-Carlo analysis and ANSYS as heat analysis tools. In addition we have prepared a Cockcroft type proton injector in order to perform experiments of proton irradiation with the target system. And we are also investigating to select a suitable intermediate material. Based on the results of the experiments, some prototypes of the beryllium target system will be produced in 2013. 3.3. Design of neutron generator device with beryllium target At present, the project team is designing not only beryllium target system but also moderator, collimator and radiation shield to form the neutron generator device. To determine conceptual design of the device, Monte-Carlo analysis using PHITS as a multi-purpose MonteCarlo code is being performed (Iwase et al., 2002). Fig. 2 shows a schematic cross-section view of the neutron generator device. Epithermal neutron flux, contaminations of fast neutron dose and gamma-ray dose at beam port were determined by the Monte-Carlo estimation while changing the parameters of material, dimensions and shape of each element. The results of the Monte-Carlo analysis demonstrated that a neutron generator model with 80 kW proton beam irradiation can generate enough epithermal neutron flux (42.0 109 n/cm2/s) at the beam port. We are performing the estimation continuously and basic design of proper neutron generator had been determined at the end of 2012. First, high energy neutrons generated at beryllium target are reduced by a fast neutron filter made of iron. And a moderator is installed behind the fast neutron filter in order to create epithermal neutrons. To reduce gamma-rays and to cut thermal neutrons in the
Fig. 3. RFQ and DLT tubes installed in the accelerator room in iNMRC.
Irradiation Ion Source
Room Patient
Neutron Generator
RFQ
DTL
Proton Beam
Accelerator Room Fig. 4. Cross section view of Tsukuba's BNCT facility in the iNMRC.
beam, bismuth filter and cadmium filter are located at the back of the moderator. Finally the epithermal neutrons are focused to beam aperture by the collimator made of polyethylene and lead. 3.4. Treatment facility To conduct actual treatment using the linac based neutron source in the near future, our team has acquired a suitable building. It is a building which is managed by Ibaraki prefecture; it is located near JAEA in Tokai village. The building has been renovated by Ibaraki Prefecture. It can house the linac-based neutron source, and can also accept high intensity neutrons in an irradiation room. The building has
Please cite this article as: Kumada, H., et al., Project for the development of the linac based NCT facility in University of Tsukuba. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.02.018i
H. Kumada et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Fig. 5. Screen shot of treatment planning with Tsukuba plan.
been completed as BNCT facility, and it was named “Ibaraki Neutron Medical Research Center” (abbreviated as, “iNMRC”) in December 2012. Both the tubes of RFQ and DTL as shown in Fig. 3 were installed in an accelerator room in iNMRC in September 2012. Fig. 4 shows layout of each device in the building. The neutron generator device was installed to a prescribed position in the irradiation room in 2013. Proton beam emitted from the linac at the neighbor room reaches the irradiation room through a separation wall and the proton beam bends, and finally the protons generate high intensity neutrons by the reaction with beryllium.
University were applied. The monitored data of patient's position by the device will be utilized for irradiation management as well as for quality assurance and quality control (QA/QC) of the therapy. Furthermore we intend to develop Prompt Gamma-ray SPECT (PG-SPECT) which can estimate directly the boron dose distribution as well as the change in boron concentration around target region during irradiation. At present, we are developing a prototype of PG-SPECT system and scintillators were applied to gammaray detector of the system.
3.5. Development of a medical equipment
4. Conclusions
For the development of a treatment planning system, a new Monte-Carlo based system (developing code; Tsukuba Plan) is under development based on fundamental technologies of JCDS (Kumada et al., 2007). JCDS has actual achievements and reliability based on application to treatment planning of clinical trials performed at JRR-4. To improve dosimetry performance of Tsukuba plan, original MontelCarlo transport engine is being developed with PHITS technologies. The Monte-Carlo transport engine can calculate behavior of neutron and photon as well as proton and heavy ions. Thus the Tsukuba Plan enables us to perform dose estimation of not only BNCT but also particle radiotherapy and X-ray therapy. And the system allows estimating total dose of combined radiotherapy. Fig. 5 shows a working view of Tsukuba Plan. A new patient positioning device is being developed together with Tsukuba Plan. The device navigates a patient to irradiation position quickly. Alignment method of the device is the employed methodology of JRR-40 s patient setting system (Kumada et al., 2000). Furthermore the device has the function of monitoring the patient's movement in real-time during irradiation. In the development of the monitoring method, fundamental technologies of real-time tracking proton radiotherapy developed in Tsukuba
The project team consisting of specialists of several research institutes headed by University of Tsukuba has launched the development of an accelerator based BNCT facility. At present 8 MeV energy proton linac is being produced. The linac tube has been completed and installed in iNMRC. Neutron generator device with a beryllium target system is being designed. The neutron generator has been constructed and installed to the irradiation room at iNMRC in 2013. The neutron generator combined with the linac will generate adequate epithermal neutrons for BNCT in 2014. Several medical devices such as treatment planning system, patient positioning device and radiation monitors will be completed by 2014. In the current schedule, a first clinical trial using the linac-based BNCT facility is planned to be performed in 2015. References Capoulat, M.E., Minsky, D.M., Kreiner, A.J., 2011. Application of the 9Be(d,n)10B reaction to AB-BNCT skin and deep tumor treatment. Appl. Radiat. Isot. 69, 1684–1687. Ceballos, C., Esposito, J., Agosteo, S., et al., 2011. Towards the final BSA modeling for the accelerator-driven BNCT facility at INFN LNL. Appl. Radiat. Isot. 69, 1660–1663.
Please cite this article as: Kumada, H., et al., Project for the development of the linac based NCT facility in University of Tsukuba. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.02.018i
H. Kumada et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎ International Atomic Energy Agency, 2001. Current status of neutron capture therapy. International Atomic Energy Agency (IAEA-TECDOC-1223) Iwase, H., Niita, K., Nakamura, T., 2002. Development of general-purpose particle and heavy ion transport Monte Carlo code. J. Nucl. Sci. Technol. 39, 1142–1151. Kumada, H. Yamamoto, K., et al., Development of the patient setting system for BNCT at JRR-4: program & abstracts, In: Proceedings of the 9th International Symposium on Neutron Capture Therapy for Cancer, 2000, p. 281.
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Kumada, H., et al., 2007. Development of JCDS, a computational dosimetry system at JAEA for boron neutron capture therapy. J. Phys. Conf. 74, 1–7. Tanaka, H., Sakurai, Y., Suzuki, M., et al., 2011. Experimental verification of beam characteristics for cyclotron-based epithermal neutron source (C-BENS). Appl. Radiat. Isot. 69, 1642–1645.
Please cite this article as: Kumada, H., et al., Project for the development of the linac based NCT facility in University of Tsukuba. Appl. Radiat. Isotopes (2014), http://dx.doi.org/10.1016/j.apradiso.2014.02.018i
