T. Mitsumoto

Experimental verification of beam characteristics for cyclotron-based epithermal neutron source (C-BENS).

A cyclotron-based epithermal neutron source has been developed for boron neutron capture therapy. This system consists of a cyclotron accelerator producing 1.1-mA proton beams with an energy of 30 MeV, a beam transport system coupled with a beryllium neutron production target, and a beam-shaping assembly (BSA) with a neutron collimator. In our previous work, the BSA was optimized to obtain sufficient epithermal neutron fluxes of ~10(9) cm(-2) s(-1) using a Monte Carlo simulation code. In order to validate the simulation results, irradiation tests using multi-foil activation at the surface of a gamma-ray shield located behind the collimator and water phantom experiments using a collimated epithermal neutron beam were performed. It was confirmed experimentally that the intensity of the epithermal neutrons was 1.2×10(9) cm(-2) s(-1).

Generation of radioisotopes with accelerator neutrons by deuterons

A new system proposed for the generation of radioisotopes with accelerator neutrons by deuterons (GRAND) is described by mainly discussing the production of 99Mo used for nuclear medicine diagnosis. A prototype facility of this system consists of a cyclotron to produce intense accelerator neutrons from the natC(\(d\),\(n\)) reaction with 40 MeV 2 mA deuteron beams, and a sublimation system to separate 99mTc from an irradiated 100MoO3 sample. About 8.1 TBq/week of 99Mo is produced by repeating irradiation on an enriched 100Mo sample (251 g) with accelerator neutrons for two days three times. It meets about 10% of the 99Mo demand in Japan. The characteristic feature of the system lies in its capability to reliably produce a wide variety of high-quality, carrier-free, carrier-added radioisotopes with a minimum level of radioactive waste without using uranium. The system is compact in size, and easy to operate; therefore it could be used worldwide to produce radioisotopes for medical, research, and industrial...

Improvement of dose distribution in phantom by using epithermal neutron source based on the Be(p,n) reaction using a 30 MeV proton cyclotron accelerator.

In order to generate epithermal neutrons for boron neutron capture therapy (BNCT), we proposed the method of filtering and moderating fast neutrons, which are emitted from the reaction between a beryllium target and 30 MeV protons accelerated by a cyclotron, using an optimum moderator system composed of iron, lead, aluminum, calcium fluoride, and enriched (6)LiF ceramic filter. At present, the epithermal-neutron source is under construction since June 2008 at Kyoto University Research Reactor Institute. This system consists of a cyclotron to supply a proton beam of about 1 mA at 30 MeV, a beam transport system, a beam scanner system for heat reduction on the beryllium target, a target cooling system, a beam shaping assembly, and an irradiation bed for patients. In this article, an overview of the cyclotron-based neutron source (CBNS) and the properties of the treatment neutron beam optimized by using the MCNPX Monte Carlo code are presented. The distribution of the RBE (relative biological effectiveness) dose in a phantom shows that, assuming a (10)B concentration of 13 ppm for normal tissue, this beam could be employed to treat a patient with an irradiation time less than 30 min and a dose less than 12.5 Gy-eq to normal tissue. The CBNS might be an alternative to the reactor-based neutron sources for BNCT treatments.

Impact of accelerator-based boron neutron capture therapy (AB-BNCT) on the treatment of multiple liver tumors and malignant pleural mesothelioma

BACKGROUND AND PURPOSE To confirm the feasibility of accelerator-based BNCT (AB-BNCT) for treatment of multiple liver tumors and malignant pleural mesothelioma (MPM), we compared dose distribution and irradiation time between AB-BNCT and reactor-based BNCT (RB-BNCT). MATERIAL AND METHODS We constructed treatment plans for AB-BNCT and RB-BNCT of four multiple liver tumors and six MPM. The neutron beam data on RB-BNCT were those from the research reactor at Kyoto University Research Reactor Institute (KURRI). The irradiation time and dose-volume histogram data were assessed for each BNCT system. RESULTS In BNCT for multiple liver tumors, when the 5 Gy-Eq dose was delivered as the mean dose to the healthy liver tissues, the mean dose delivered to the liver tumors by AB-BNCT and RB-BNCT was 68.1 and 65.1 Gy-Eq, respectively. In BNCT for MPM, when the mean lung dose to the normal ipsilateral lung was 5 Gy-Eq, the mean dose delivered to the MPM tumor by AB-BNCT and RB-BNCT was 20.2 and 19.9 Gy-Eq, respectively. Dose distribution analysis revealed that AB-BNCT is superior to RB-BNCT for treatment of deep-seated tumors. CONCLUSIONS The feasibility of the AB-BNCT system constructed at our institute was confirmed from a clinical viewpoint in BNCT for multiple liver tumors and MPM.

A phantom experiment for the evaluation of whole body exposure during BNCT using cyclotron-based epithermal neutron source (C-BENS).

At Kyoto University Research Reactor Institute (KURRI), cyclotron-based epithermal neutron source was installed in December 2008, and the supplementary construction works have been performed. As of December 2010, the various irradiation characteristics important for BNCT were mostly evaluated. The whole body exposure during BNCT medical irradiation is one of the important characteristics. In this article, measurements of absorbed dose for thermal and fast neutrons and gamma-ray at ten positions corresponding to important organs are reported.

Development of a high current H− ion source for cyclotronsa)

A multi-cusp DC H(-) ion source has been designed and fabricated for medical applications of cyclotrons. Optimization of the ion source is in progress, such as the improvement of the filament configuration, magnetic filter strength, extraction electrodes shape, configuration of electron suppression magnets, and plasma electrode material. A small quantity of Cs has been introduced into the ion source to enhance the negative ion beam current. The ion source produced 16 mA of DC H(-) ion beam with the Cs-seeded operation at a low arc discharge power of 2.8 kW.

High current DC negative ion source for cyclotron

A filament driven multi-cusp negative ion source has been developed for proton cyclotrons in medical applications. In Cs-free operation, continuous H(-) beam of 10 mA and D(-) beam of 3.3 mA were obtained stably at an arc-discharge power of 3 kW and 2.4 kW, respectively. In Cs-seeded operation, H(-) beam current reached 22 mA at a lower arc power of 2.6 kW with less co-extracted electron current. The optimum gas flow rate, which gives the highest H(-) current, was 15 sccm in the Cs-free operation, while it decreased to 4 sccm in the Cs-seeded operation. The relationship between H(-) production and the design/operating parameters has been also investigated by a numerical study with KEIO-MARC code, which gives a reasonable explanation to the experimental results of the H(-) current dependence on the arc power.

Evaluation of thermal neutron irradiation field using a cyclotron-based neutron source for alpha autoradiography.

It is important to measure the microdistribution of (10)B in a cell to predict the cell-killing effect of new boron compounds in the field of boron neutron capture therapy. Alpha autoradiography has generally been used to detect the microdistribution of (10)B in a cell. Although it has been performed using a reactor-based neutron source, the realization of an accelerator-based thermal neutron irradiation field is anticipated because of its easy installation at any location and stable operation. Therefore, we propose a method using a cyclotron-based epithermal neutron source in combination with a water phantom to produce a thermal neutron irradiation field for alpha autoradiography. This system can supply a uniform thermal neutron field with an intensity of 1.7×10(9) (cm(-2)s(-1)) and an area of 40mm in diameter. In this paper, we give an overview of our proposed system and describe a demonstration test using a mouse liver sample injected with 500mg/kg of boronophenyl-alanine.

Evaluation for activities of component of Cyclotron-Based Epithermal Neutron Source (C-BENS) and the surface of concrete wall in irradiation room.

The workers employed in BNCT must enter the irradiation room just after an irradiation under the condition of remaining activities. To reduce the radiation exposure for the workers, it is important to identify the origins of the activities. In this research, the activities induced on the concrete wall surface were evaluated using MCNP-5 and the measurement results of thermal neutron distribution. Furthermore, the radioisotopes produced in the moderator were identified with a High Purity Germanium detector. It was found that the activities of the wall were mainly caused by (46)Sc, (60)Co and (152)Eu, and that (24)Na and (56)Mn were mainly produced in the moderator.

Development of a 20 mA negative hydrogen ion source for cyclotrons

A cesiated DC negative ion source has been developed for proton cyclotrons in medical applications. A continuous H− beam of 23 mA was stably extracted at an arc power of 3 kW. The beam current gradually decreases with a constant arc power and without additional Cs injection and the decay rate was about 0.03 mA (0.14%) per hour. A feed-back control system that automatically adjusts the arc power to stabilize the beam current is able to keep the beam current constant at ±0.04 mA (±0.2%).