Tooru Kobayashi

Indications of neutrino oscillation in a 250 km long-baseline experiment.

The K2K experiment observes indications of neutrino oscillation: a reduction of nu(mu) flux together with a distortion of the energy spectrum. Fifty-six beam neutrino events are observed in Super-Kamiokande (SK), 250 km from the neutrino production point, with an expectation of 80.1(+6.2)(-5.4). Twenty-nine one ring mu-like events are used to reconstruct the neutrino energy spectrum, which is better matched to the expected spectrum with neutrino oscillation than without. The probability that the observed flux at SK is explained by statistical fluctuation without neutrino oscillation is less than 1%.

Analytical Calculation of Boron-10 Dosage in Cell Nucleus for Neutron Capture Therapy

The following measures of physical effects in a spherical cell nucleus, resulting from heavy charged particles caused by thermal neutron reactions in tissue, were evaluated by analytical calculatio...

Microanalysis system of ppm-order 10B concentrations in tissue for neutron capture therapy by prompt gamma-ray spectrometry

For neutron capture therapy, a new technique for measuring 10B concentrations of ppm order in tissue has been developed by using 10B(n, α)7Li∗ prompt gamma-ray spectrometry. The measuring system consists of a Ge(Li) detector and a 6LiF tile neutron shield attached to the neutron guide tube of the Kyoto University Reactor (KUR) with very low background gamma-rays. The 10B concentrations of unknown samples were determined in comparison with gamma-ray data obtained from known samples. The detection limit of the system is 0.1-0.5 ppm 10B concentration. In the practical use of the system for neutron capture therapy, 10B concentrations of 10 ppm, which is ordinarily pre-injected into the tumor, can be measured in less than 30 s with 10% accuracy by using 1 g samples. Moreover, the system has the advantage that pre-treatment of the sample is not required. As a neutron monitor in a homogeneous sample, gamma-rays emitted from H(n, γ)D reactions are used. Therefore, neutron irradiation conditions of this system, i.e. fluence rate, energy spectrum, and distribution in the sample do not affect the analyzing results, and the quantity and dimensions of the sample are also not restricted.

Gadolinium neutron-capture therapy using novel gadopentetic acid–chitosan complex nanoparticles: in vivo growth suppression of experimental melanoma solid tumor

The potential of gadolinium neutron-capture therapy (Gd-NCT) for cancer was evaluated using chitosan nanoparticles as a novel gadolinium device. The nanoparticles, incorporating 1200 microg of natural gadolinium, were administered intratumorally twice in mice bearing subcutaneous B16F10 melanoma. The thermal neutron irradiation was performed for the tumor site, with the fluence of 6. 32x10(12) neutrons/cm(2), 8 h after the second gadolinium administration. After the irradiation, the tumor growth in the nanoparticle-administered group was significantly suppressed compared to that in the gadopentetate solution-administered group, despite radioresistance of melanoma and the smaller Gd dose than that administered in past Gd-NCT trials. This study demonstrated the potential usefulness of Gd-NCT using gadolinium-loaded nanoparticles.

The Remodeling and Basic Characteristics of the Heavy Water Neutron Irradiation Facility of the Kyoto University Research Reactor, Mainly for Neutron Capture Therapy

The Heavy Water Thermal Neutron Facility of the Kyoto University Research Reactor (KUR) was wholly updated in March 1996 mainly for neutron capture therapy. The performance as a neutron irradiation facility was improved using the epithermal neutron moderator of the aluminum-heavy water mixture (Al/D2O = 80/20 vol%), the neutron energy spectrum shifter of heavy water, and the thermal neutron filters of cadmium and boral plates. The clinical irradiation utilization under the full-power (5-MW) continuous KUR operation was realized employing both the radiation shielding system, consisting of the shielding door and irradiation room, and the remote carrying system for a patient. The safety and utility of the facility were improved due to the safety observation system.

A noninvasive dose estimation system for clinical BNCT based on PG-SPECT--conceptual study and fundamental experiments using HPGe and CdTe semiconductor detectors.

A noninvasive method for measuring the absorbed dose distribution during the administration of clinical boron neutron capture therapy (BNCT) using an online three-dimensional (3D) imaging system is presented. This system is designed to provide more accurate information for treatment planning and dosimetry. The single-photon emission computed tomography (SPECT) technique is combined with prompt gamma-ray analysis (PGA) to provide an ideal dose estimation system for BNCT. This system is termed PG-SPECT. The fundamental feasibility of the PG-SPECT system for BNCT is confirmed under the following conditions: (1) a voxel size of 1 x 1 x 1 cm3, comparable to the spatial resolution of our standard dosimetric technique using gold wire activation, where data are available for every 5-10 mm of wire length; (2) a reaction rate of 10B(n,alpha)7Li within the measurement volume is greater than 1.1 x l0(6) interactions/cm3/s, corresponding to a thermal neutron flux of 5 x 10(8) n/cm2/s and a 10B concentration of greater than 10 ppm for the deepest part of the tumor volume under typical BNCT clinical conditions; (3) statistical uncertainty of the count rate for 10B(n,alpha)7Li prompt gamma rays is 10% or less. The desirable characteristics of a detector for the PG-SPECT system were determined by basic experiments using both HPGe and CdTe semiconductor detectors. The CdTe semiconductor detector has the greatest potential for this system because of its compactness and simplicity of maintenance.

The relative biological effectiveness of 10B-neutron capture therapy for early skin reaction in the hamster.

The relative biological effectiveness (RBE) of 10B-neutron capture therapy (BNCT) on skin was analyzed using hamsters. The Kyoto University Research Reactor, which has a very low contamination of gamma rays and fast neutrons, was used as a thermal neutron source. Boron-10-para-boronophenylalanine hydrochloride ([10B]BPA.HCl) was administered to the hamsters. The evolution and time course of early skin reactions were assessed. These reactions were compared with those produced by electron beams. The maximum safe skin doses (no more than moist desquamation) of BNCT and electron beams were established to be 11 and 21 Gy, respectively. The RBE at this single dose with BNCT was found to be 1.94, assuming that the RBE of the gamma rays was 1.0 and each component of BNCT (mixed radiations) was simply additive.

Cell Inactivation and DNA Single- and Double-strand Breaks in Cultured Mammalian Cells Irradiated by a Thermal Neutron Beam

The effects on the cellular viability and induction and repair kinetics of DNA strand breaks in HeLa cells were examined after exposure to a thermal neutron beam and compared with those after gamma-irradiation. The thermal neutron survival curve had no initial shoulder. The relative biological effectiveness (r.b.e.) value of the neutron beam was determined to be 2.2 for cell killing (ratio of D0 values), 1.8 and 0.89 for single strand breakage (ssb) by alkaline sedimentation and alkaline elution respectively, and for double strand breakage (dsb) 2.6 by neutral elution. No difference was observed between thermal neutrons and gamma-rays in the repair kinetics of ssb and dsb. It is suggested that the effect induced by the intracellular nuclear reaction, 14N(n,p)14C is mainly responsible for the high r.b.e. values observed.

Neutron-capture therapy of murine ascites tumor with gadolinium-containing microcapsules

SummaryGadolinium-containing microcapsules were evaluated as an agent for gadolinium neutron-capture therapy. Mice were inoculated intraperitoneally with 107 Ehrlich ascites tumor cells and gadolinium microcapsules and exposed to thermal neutrons for 12 min (approximately 1.86×1012 neutrons cm−2). Significantly more mice given gadolinium microcapsules than those given placebo microcapsules or control survived for 60 days and considerably longer (P<0.0001), indicating that gadolinium neutron-capture reactions effectively suppressed the growth of ascites tumor cells in mice. The results suggest that these microcapsules are an effective gadolinium carrier for neutron-capture therapy.

Advances in the Control of Human Cutaneous Primary and Metastatic Melanoma by Thermal Neutron Capture Therapy

Differing in principle from boron neutron capture therapy (NCT) of brain tumors using passive accumulation of 10B, since 1972 our ideal) has been to develop a new 10B delivery system actively targeting cancers by utilizing their enhanced specific metabolic activity. As a prototype, we have been working with melanoma using 10B1-p-boronophenylalanine (10B1-BPA), a 10B-dopaanalogue, melanogenesis-seeking melanin polymer substrate2).