Recently, exploitation of cerebrospinal fluid (CSF) circulation has become increasingly recognized as a feasible strategy to solve the challenges involved in drug delivery for treating brain tumors. Boron neutron capture therapy (BNCT) also faces challenges associated with the development of an efficient delivery system for boron, especially to brain tumors. Our laboratory has been developing a system for boron delivery to brain cells using CSF, which we call the “boron CSF administration method”. In our previous study, we found that boron was efficiently delivered to the brain cells of normal rats in the form of small amounts of L-p-boronophenylalanine (BPA) using the CSF administration method. In the study described here, we carried out experiments with brain tumor model rats to demonstrate the usefulness of the CSF administration method for BNCT. We first investigated the boron concentration of the brain cells every 60 min after BPA administration into the lateral ventricle of normal rats. Second, we measured and compared the boron concentration in the melanoma model rats after administering boron via either the CSF administration method or the intravenous (IV) administration method, with estimation of the T/N ratio. Our results revealed that boron injected by the CSF administration method was excreted quickly from normal cells, resulting in a high T/N ratio compared to that of IV administration. In addition, the CSF administration method resulted in high boron accumulation in tumor cells. In conclusion, we found that using our developed CSF administration method results in more selective delivery of boron to the brain tumor compared with the IV administration method.

The newly developed Cs2LiYCl6:Ce crystal with 7Li-enrichment (CLYC7) scintillators had been utilized as a key component in a compact neutron emission spectrometer (CNES) at the Large Helical Device (LHD). The CNES was employed to enhance understanding the slowing-down process of neutral-beam-injected energetic beam deuterons by measuring the Doppler broadening of beam-driven deuterium-deuterium neutrons. In order to assess the detection capabilities in fusion neutron spectroscopy and to gain understanding into the energy spectrum at various neutron energies, a understanding of the response function of the detector across a wide neutron energy range is essential. Therefore, before implementing the CNES at the LHD, the detector was tested at high-performance neutron source facilities to evaluate its response to both thermal and fast neutrons. The detector exhibited excellent pulse shape discrimination properties. However, it also exhibited complexity through the 35Cl(n,p)35S and 35Cl(n,α)32P reactions in the fast neutron measurement. To emphasize the accuracy and reliability of the detector’s response, particularly in the fast neutron energy range, Monte Carlo N-Particle transport simulations were employed. In order to validate the experimental results against the calculations, an energy-dependent quenching factor was determined. This analysis provided a clear understanding of the CLYC7 scintillation detector and its potential in the context of fusion neutron spectroscopy for applications in the LHD and future fusion devices.

In recent years, various drug delivery systems circumventing the blood–brain barrier have emerged for treating brain tumors. This study aimed to improve the efficacy of brain tumor treatment in boron neutron capture therapy (BNCT) using cerebrospinal fluid (CSF) circulation to deliver boronophenylalanine (BPA) to targeted tumors. Previous experiments have demonstrated that boron accumulation in the brain cells of normal rats remains comparable to that after intravenous (IV) administration, despite BPA being administered via CSF at significantly lower doses (approximately 1/90 of IV doses). Based on these findings, BNCT was conducted on glioma model rats at the Kyoto University Research Reactor Institute (KUR), with BPA administered via CSF. This method involved implanting C6 cells into the brains of 8-week-old Wistar rats, followed by administering BPA and neutron irradiation after a 10-day period. In this study, the rats were divided into four groups: one receiving CSF administration, another receiving IV administration, and two control groups without BPA administration, with one subjected to neutron irradiation and the other not. In the CSF administration group, BPA was infused from the cisterna magna at 8 mg/kg/h for 2 h, while in the IV administration group, BPA was intravenously administered at 350 mg/kg via the tail vein over 1.5 h. Thermal neutron irradiation (5 MW) for 20 min, with an average fluence of 3.8 × 10¹²/cm², was conducted at KUR’s heavy water neutron irradiation facility. Subsequently, all of the rats were monitored under identical conditions for 7 days, with pre- and post-irradiation tumor size assessed through MRI and pathological examination. The results indicate a remarkable therapeutic efficacy in both BPA-administered groups (CSF and IV). Notably, the rats treated with CSF administration exhibited diminished BPA accumulation in normal tissue compared to those treated with IV administration, alongside maintaining excellent overall health. Thus, CSF-based BPA administration holds promise as a novel drug delivery mechanism in BNCT.