Abstract：
BACKGROUND: Evaluation of the boron dose is essential for boron neutron capture therapy (BNCT). Nevertheless, a direct evaluation method for the boron-dose distribution has not yet been established in the clinical BNCT field. To date, even in quality assurance (QA) measurements, the boron dose has been indirectly evaluated from the thermal neutron flux measured using the activation method with gold foil or wire and an assumed boron concentration in the QA procedure. Recently, we successfully conducted optical imaging of the boron-dose distribution using a cooled charge-coupled device (CCD) camera and a boron-added liquid scintillator at the E-3 port facility of the Kyoto University Research Reactor (KUR), which supplies an almost pure thermal neutron beam with very low gamma-ray contamination. However, in a clinical accelerator-based BNCT facility, there is a concern that the boron-dose distribution may not be accurately extracted because the unwanted luminescence intensity, which is irrelevant to the boron dose is expected to increase owing to the contamination of fast neutrons and gamma rays.
OBJECTIVE: The purpose of this research was to study the validity of a newly proposed method using a boron-added liquid scintillator and a cooled CCD camera to directly observe the boron-dose distribution in a clinical accelerator-based BNCT field.
METHODS: A liquid scintillator phantom with 10 B was prepared by filling a small quartz glass container with a commercial liquid scintillator and boron-containing material (trimethyl borate); its natural boron concentration was 1 wt%. Luminescence images of the boron-neutron capture reaction were obtained in a water tank at several different depths using a CCD camera. The contribution of background luminescence, mainly due to gamma rays, was removed by subtracting the luminescence images obtained using another sole liquid scintillator phantom (natural boron concentration of 0 wt%) at each corresponding depth, and a depth profile of the boron dose with several discrete points was obtained. The obtained depth profile was compared with that of calculated boron dose, and those of thermal neutron flux which were experimentally measured or calculated using a Monte Carlo code.
RESULTS: The depth profile evaluated from the subtracted images indicated reasonable agreement with the calculated boron-dose profile and thermal neutron flux profiles, except for the shallow region. This discrepancy is thought to be due to the contribution of light reflected from the tank wall. The simulation results also demonstrated that the thermal neutron flux would be severely perturbed by the 10 B-containing phantom if a relatively larger container was used to evaluate a wide range of boron-dose distributions in a single shot. This indicates a trade-off between the luminescence intensity of the 10 B-added phantom and its perturbation effect on the thermal neutron flux.
CONCLUSIONS: Although a partial discrepancy was observed, the validity of the newly proposed boron-dose evaluation method using liquid-scintillator phantoms with and without 10 B was experimentally confirmed in the neutron field of an accelerator-based clinical BNCT facility. However, this study has some limitations, including the trade-off problem stated above. Therefore, further studies are required to address these limitations.
OBJECTIVE: The purpose of this research was to study the validity of a newly proposed method using a boron-added liquid scintillator and a cooled CCD camera to directly observe the boron-dose distribution in a clinical accelerator-based BNCT field.
METHODS: A liquid scintillator phantom with 10 B was prepared by filling a small quartz glass container with a commercial liquid scintillator and boron-containing material (trimethyl borate); its natural boron concentration was 1 wt%. Luminescence images of the boron-neutron capture reaction were obtained in a water tank at several different depths using a CCD camera. The contribution of background luminescence, mainly due to gamma rays, was removed by subtracting the luminescence images obtained using another sole liquid scintillator phantom (natural boron concentration of 0 wt%) at each corresponding depth, and a depth profile of the boron dose with several discrete points was obtained. The obtained depth profile was compared with that of calculated boron dose, and those of thermal neutron flux which were experimentally measured or calculated using a Monte Carlo code.
RESULTS: The depth profile evaluated from the subtracted images indicated reasonable agreement with the calculated boron-dose profile and thermal neutron flux profiles, except for the shallow region. This discrepancy is thought to be due to the contribution of light reflected from the tank wall. The simulation results also demonstrated that the thermal neutron flux would be severely perturbed by the 10 B-containing phantom if a relatively larger container was used to evaluate a wide range of boron-dose distributions in a single shot. This indicates a trade-off between the luminescence intensity of the 10 B-added phantom and its perturbation effect on the thermal neutron flux.
CONCLUSIONS: Although a partial discrepancy was observed, the validity of the newly proposed boron-dose evaluation method using liquid-scintillator phantoms with and without 10 B was experimentally confirmed in the neutron field of an accelerator-based clinical BNCT facility. However, this study has some limitations, including the trade-off problem stated above. Therefore, further studies are required to address these limitations.
摘要：
背景：评估硼剂量对于硼中子俘获疗法（BNCT）至关重要。然而，临床BNCT领域尚未建立硼剂量分布的直接评价方法.迄今为止,即使在质量保证(QA)测量中，硼剂量已通过使用金箔或金属丝的活化方法测量的热中子通量以及QA程序中假定的硼浓度间接评估。最近,我们在京都大学研究堆（KUR）的E-3端口设施使用冷却的电荷耦合器件（CCD）相机和添加硼的液体闪烁体成功地进行了硼剂量分布的光学成像，它提供了几乎纯的热中子束，具有非常低的伽马射线污染。然而,在基于临床加速器的BNCT设施中，担心硼剂量分布可能无法准确提取，因为不需要的发光强度，由于快中子和伽马射线的污染，预计与硼剂量无关的硼剂量会增加。
目的：这项研究的目的是研究一种新提出的方法的有效性，该方法使用添加硼的液体闪烁体和冷却的CCD相机直接观察基于临床加速器的BNCT场中的硼剂量分布。
方法:通过用商业液体闪烁体和含硼材料(硼酸三甲酯)填充小石英玻璃容器来制备具有IOB的液体闪烁体体模;其天然硼浓度为1重量%。使用CCD相机在水箱中的几个不同深度处获得了硼中子俘获反应的发光图像。背景发光的贡献，主要是由于伽马射线,通过减去使用另一个单独的液体闪烁体模（0重量%的天然硼浓度）在每个相应的深度获得的发光图像来去除，并获得了具有几个离散点的硼剂量的深度分布。将获得的深度分布与计算的硼剂量进行比较，以及使用蒙特卡洛代码进行实验测量或计算的热中子通量。
结果：从减影图像评估的深度分布表明与计算的硼剂量分布和热中子通量分布合理一致，除了浅层区域。这种差异被认为是由于从罐壁反射的光的贡献。模拟结果还表明，如果使用相对较大的容器来评估单次发射中的各种硼剂量分布，则含10B的体模将严重干扰热中子通量。这表明添加10B的体模的发光强度与其对热中子通量的扰动效应之间存在权衡。
结论：尽管观察到部分差异，在基于加速器的临床BNCT设施的中子场中，实验证实了使用具有和不具有10B的液体闪烁体模的新提出的硼剂量评估方法的有效性。然而,这项研究有一些局限性，包括上述权衡问题。因此,需要进一步的研究来解决这些局限性.
目的：这项研究的目的是研究一种新提出的方法的有效性，该方法使用添加硼的液体闪烁体和冷却的CCD相机直接观察基于临床加速器的BNCT场中的硼剂量分布。
方法:通过用商业液体闪烁体和含硼材料(硼酸三甲酯)填充小石英玻璃容器来制备具有IOB的液体闪烁体体模;其天然硼浓度为1重量%。使用CCD相机在水箱中的几个不同深度处获得了硼中子俘获反应的发光图像。背景发光的贡献，主要是由于伽马射线,通过减去使用另一个单独的液体闪烁体模（0重量%的天然硼浓度）在每个相应的深度获得的发光图像来去除，并获得了具有几个离散点的硼剂量的深度分布。将获得的深度分布与计算的硼剂量进行比较，以及使用蒙特卡洛代码进行实验测量或计算的热中子通量。
结果：从减影图像评估的深度分布表明与计算的硼剂量分布和热中子通量分布合理一致，除了浅层区域。这种差异被认为是由于从罐壁反射的光的贡献。模拟结果还表明，如果使用相对较大的容器来评估单次发射中的各种硼剂量分布，则含10B的体模将严重干扰热中子通量。这表明添加10B的体模的发光强度与其对热中子通量的扰动效应之间存在权衡。
结论：尽管观察到部分差异，在基于加速器的临床BNCT设施的中子场中，实验证实了使用具有和不具有10B的液体闪烁体模的新提出的硼剂量评估方法的有效性。然而,这项研究有一些局限性，包括上述权衡问题。因此,需要进一步的研究来解决这些局限性.
