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A LiF-Si-based active neutron detector was developed for the measurement of real-time BNCT neutron beam. Thermal-neutron detection efficiencies were adjustable to the neutron beam intensities at various measurement locations by simply exchanging the LiF neutron converter, while minimizing sensitivity to photons. The neutron detection efficiency ranges from 8 × 10−7 to 8 × 10−4 cm2. The thermal-neutron detection efficiencies were experimentally obtained by placing the neutron detectors inside an education reactor. Experimental results were verified using a Monte Carlo simulation technique. The simulated thermal-neutron detection efficiencies were in good agreement with the experimental results within the range of experimental uncertainties. Discrepancies in both sets of results were due to an insufficient assessment of LiF density and flatness. Surface-density neutron detection efficiencies were proposed to more accurately measure neutron fluence rates. • LiF-Si-based active neutron detector was developed for measurement of BNCT beam. • Thermal-neutron detection efficiencies were experimentally obtained at UTR-KINKI. • Experimental results were verified using a Monte Carlo simulation technique. • Thermal-neutron detection efficiency can be tailored to neutron beam intensity. • The neutron detection efficiency ranges from 8 × 10−7 to 8 × 10−4 cm2. [ABSTRACT FROM AUTHOR]

Purpose: Fast neutron, gamma-ray, and boron doses have different relative biological effectiveness (RBE). In boron neutron capture therapy (BNCT), the clinical dose is the total of these dose components multiplied by their RBE. Clinical dose monitoring is necessary for quality assurance of the irradiation profile; therefore, the fast neutron, gamma-ray, and boron doses should be separately monitored. To estimate these doses separately, and to monitor the boron dose without monitoring the thermal neutron fluence, the authors propose a triple ionization chamber method using graphitewalled carbon dioxide gas (C-CO2), tissue-equivalent plastic-walled tissue-equivalent gas (TE-TE), and boron-loaded tissue-equivalent plastic-walled tissue-equivalent gas [TE(B)-TE] chambers. To use this method for dose monitoring for a neutron and gamma-ray field moderated by D2O from a Be-covered Li target (Be-covered Li BNCT field), the relative sensitivities of these ionization chambers are required. The relative sensitivities of the TE-TE, C-CO2, and TE(B)-TE chambers to fast neutron, gamma-ray, and boron doses are calculated with the particle and heavy-ion transport code system (PHITS). Methods: The relative sensitivity of the TE(B)-TE chamber is calculated with the same method as for the TE-TE and C-CO2 chambers in the paired chamber method. In the Be-covered Li BNCT field, the relative sensitivities of the ionization chambers to fast neutron, gamma-ray, and boron doses are calculated from the kerma ratios, mass attenuation coefficient tissue-to-wall ratios, and W-values. The Be-covered Li BNCT field consists of neutrons and gamma-rays which are emitted from a Be-covered Li target, and this resultant field is simulated by using PHITS with the cross section library of ENDF-VII. The kerma ratios and mass attenuation coefficient tissue-to-wall ratios are determined from the energy spectra of neutrons and gamma-rays in the Be-covered Li BNCT field. The W-value is calculated from recoil charged particle spectra by the collision of neutrons and gamma-rays with the wall and gas materials of the ionization chambers in the gas cavities of TE-TE, C-CO2, and TE(B)-TE chambers (10B concentrations of 10, 50, and 100 ppm in the TE-wall). Results: The calculated relative sensitivity of the C-CO2 chamber to the fast neutron dose in the Be-covered Li BNCT field is 0.029, and those of the TE-TE and TE(B)-TE chambers are both equal to 0.965. The relative sensitivities of the C-CO2, TE-TE, and TE(B)-TE chambers to the gamma-ray dose in the Be-covered Li BNCT field are all 1 within the 1% calculation uncertainty. The relative sensitivities of TE(B)-TE to boron dose with concentrations of 10, 50, and 100 ppm 10B are calculated to be 0.865 times the ratio of the in-tumor to in-chamber wall boron concentration. Conclusions: The fast neutron, gamma-ray, and boron doses of a tumor in-air can be separately monitored by the triple ionization chamber method in the Be-covered Li BNCT field. The results show that these doses can be easily converted to the clinical dose with the depth correction factor in the body and the RBE. [ABSTRACT FROM AUTHOR]

Abstract: The characteristics of moderator assembly dimension was investigated for the usage of 7Li(p,n) neutrons by 2.3–2.8MeV protons and W(p,n) neutrons by 50MeV protons. The indexes were the treatable protocol depth (TPD) and advantage depth (AD). Consequently, a configuration for W target with the Fe filter, Fluental moderator, Pb reflector showed the TPD of 5.8cm and AD of 9.3cm. Comparable indexes were found for the Li target in a geometry with the MgF2 moderator and Teflon reflector. [Copyright &y& Elsevier]

Abstract: The imaging plate (IP) technique is tried to be used as a handy method to measure the spatial neutron distribution via the 157Gd(n,γ)158Gd reaction for neutron capture therapy (NCT). For this purpose, IP is set in a water phantom and irradiated in a mixed field of neutrons and γ-rays. The Hiroshima University Radiobiological Research Accelerator is utilized for this experiment. The neutrons are moderated with 20-cm-thick D2O to obtain suitable neutron field for NCT. The signal for IP doped with Gd as a neutron-response enhancer is subtracted with its contribution by γ-rays, which was estimated using IP without Gd. The γ-ray response of Gd-doped IP to non-Gd IP is set at 1.34, the value measured for 60Co γ-rays, in estimating the γ-ray contribution to Gd-doped IP signal. Then measured distribution of the 157Gd(n,γ)158Gd reaction rate agrees within 10% with the calculated value based on the method that has already been validated for its reproducibility of Au activation. However, the evaluated distribution of the 157Gd(n,γ)158Gd reaction rate is so sensitive to γ-ray energy, e.g. the discrepancy of the 157Gd(n,γ)158Gd reaction rate between measurement and calculation becomes 30% for the photon energy change from 33keV to 1.253MeV. [Copyright &y& Elsevier]

Background Purpose Methods Results Conclusions Boron neutron capture therapy (BNCT) is a next‐generation radiotherapy, utilizing both an external neutron beam and a 10B$^{10}{\rm B}$‐containing pharmaceutical. A compact accelerator for a high intensity neutron source was installed to conduct BNCT in a hospital. The dose administered to a patient was evaluated by measuring the proton beam current.Neutron intensity should be monitored in real‐time by measuring the neutrons emitted from the target during BNCT irradiation. This is crucial due to potential neutron target degradation. Online neutron beam monitoring systems are required for reliable measurements of the administered neutron dose. An online neutron beam monitoring system was developed to monitor neutron intensity irradiating on the patient at the National Cancer Center Hospital (NCCH).The neutron detector comprised a back‐illuminated thin Si diode of 40‐μm$\umu{\rm m}$ thickness and an ultrathin natural LiF neutron converter of 0.05‐μm$\umu{\rm m}$ thickness. The neutron detector was installed on the neutron target unit, regardless of whether a patient was present, without any additional modifications to the setup. The response functions for high photon dose rates of upto 100 Gy/h were measured. The pulse heights were measured using the neutron beam monitor during BNCT neutron irradiation. Neutron temporal response measured using the online beam monitor was acquired and compared with the proton beam current and the measurements at a patient position. From this measurement at the patient position, the neutron fluence rate irradiating on a patient was obtained.The neutron events were separated from the photon events. The neutron counting rates increased rapidly with the starting of proton beam irradiation and dropped to zero upon its termination. During intermittent drops and recoveries in the proton beam, the neutron beam monitor for counting rates responded quickly, synchronizing with the beam current. A scatter plot of the neutron counting rate and proton beam current indicated a good linear correlation. A direct relationship between the online neutron beam monitor's neutron counting rates and those of the patient neutron detector showed a good correlation coefficient of 0.84. A ratio of the both neutron counting rates showed a standard deviation of 6%. The correlation coefficient and standard deviation were improved to 0.94 and 1.5%, by re‐binning the neutron temporal response with longer acquisition period than 1 s. Using the online neutron beam monitor, the neutron fluence rate was obtained from the direct relationship within 1.5%. Therefore, real‐time monitoring of neutron intensity was achieved within the acceptable level as per the International Commission on Radiation Units and Measurements report.The online neutron beam monitoring system was developed to monitor the BNCT neutron beam intensity at NCCH. The temporal response of the neutron beam monitor was synchronized with the neutron counting rate at the patient position. Using the online neutron beam monitor, the neutron fluence rate irradiating on the patient can be monitored from the direct relationship. Fluctuation of the neutron beam intensity through BNCT irradiation and the degradation of the lithium target through the lifespan of the neutron target could be monitored using the neutron beam monitor. [ABSTRACT FROM AUTHOR]

The converter configuration for a multi-imaging plate system was investigated for the application of quality assurance in the irradiation field profile for boron neutron capture therapy. This was performed by the simulation calculation using the PHITS code in the fields at the Heavy Water Neutron Irradiation Facility of Kyoto University Reactor. The converter constituents investigated were carbon for gamma rays, and polyethylene with and without LiF at varied 6 Li concentration for thermal, epithermal, and fast neutrons. Consequently, potential combinations of the converters were found for two components, gamma rays and thermal neutrons, for the standard thermal neutron mode and three components of gamma rays, epithermal neutrons, and thermal or fast neutrons, for the standard mixed or epithermal neutron modes, respectively. [ABSTRACT FROM AUTHOR]

Quality assurance of the spatial distributions of neutrons and gamma rays was tried using imaging plates (IPs) and converters to enhance the beam components in the epithermal neutron mode of the Kyoto University Reactor. The converters used were 4 mm thick epoxy resin with B 4 C at 6.85 weight-percent (wt%) 10 B for epithermal neutrons, and 3 mm thick carbon for gamma rays. Results suggested that the IP signal does not need a sensitivity correction regardless of the incident radiation that produces it. [ABSTRACT FROM AUTHOR]

We designed a neutron spectrometer to measure low-energy neutron beam for boron neutron capture therapy (BNCT) without exchanging thicknesses of neutron moderator. The spectrometer consists of a boron carbide block as a neutron moderator and nine thin neutron silicon sensors with variable detection efficiency. Using the Monte Carlo technique, we simulated the spectrometer's neutron energy response functions. It represented sharp rise in the response functions with various lower limits of neutron energies distributed over a wide range of neutron energy from a thermal energy to a few 100 keV. The lower limit of neutron energy was dependent on a depth in the boron carbide block. By applying thicker enriched 6LiF neutron converter and covering the deep positioned neutron sensors with polyethylene plates, neutron detection efficiencies were increased to be able to measure the BNCT neutron beam in a short time. • Low-energy neutron spectrometer was designed for Boron Neutron Capture Therapy. • Spectrometer consists of thin neutron sensors covered with boron neutron absorber. • Single measurement provide neutron energy spectrum without exchanging moderators. • Spectrometer response functions have been simulated using Monte Carlo technique. • Verification is evaluated to measure neutron energy beam from simulation results. [ABSTRACT FROM AUTHOR]

We have developed a new real-time neutron detector, which is able to measure a direct neutron beam of boron neutron capture therapy. The detector consists of both a 40- μ m-thick pn diode and around 0.09- μ m-thick LiF neutron converter. Experimental results indicate that this neutron detector can measure neutron flux up to 1 × 10 9 (cm−2 s−1), separately from gamma rays around 500 mGy/h. The measured depth distribution of neutron flux in an acrylic block is in agreement with the activation results of gold. • New real-time neutron detector have been developed for BNCT using thin silicon sensor. • Neutron detector can measure BNCT neutron beam with high fluxes of 1 × 10 9 (cm−2 s−1). • Neutron events can be clearly separated from gamma-ray events with high dose rates. • Measured neutron depth distribution is in agreement with neutron activation analysis. • The detector can measure rates of boron neutron capture reaction at every moment. [ABSTRACT FROM AUTHOR]

A real-time neutron detector was developed to measure an intense neutron beam, based on both a thin silicon sensor and an extremely thin neutron converter for boron neutron capture therapy (BNCT). Neutron response function and detection efficiency were evaluated at the BNCT facility. The response function consists of neutron events, detecting both triton particles produced from the 6Li (n,t)4He reaction and alpha particles from the 10B (n,α)7Li reaction. The detector is able to clearly separate the BNCT neutron beam from coexisted gamma rays. A depth distribution of slow neutron flux in an acrylic block was experimentally obtained. While the relative depth distribution of over 20 mm in depth is in line with the results of the neutron activation measurements of gold, the absolute values are around 17% smaller than the corresponding neutron activation results, which was due to the incomplete evaluation of the neutron detection efficiency and angular-dependent response of the neutron detector. • Real-time neutron detector to be able to measure intense neutron beam. • Neutron beam for boron neutron capture therapy can be followed in a real time. • Neutron response function consists of secondary particles produced both neutron-lithium and neutron-boron reactions. • The neutron detector is composed of thin Si pn diode and extremely thin LiF neutron converter. • Linearity of neutron detection was experimentally obtained. [ABSTRACT FROM AUTHOR]