Optical imaging that detects Cerenkov-light or the luminescence of water is a promising method to measure dose distributions in radiotherapy due to its ability to provide high-resolution images in a short measurement time. However, it is unclear whether optical imaging is possible for neutron beams in water. Although neutrons do not emit light in water, prompt gamma photons or protons produced from the interaction between neutrons and water may emit light. To clarify this point, we measured the light distribution in water during irradiation of neutron beams from a boron neutron capture therapy (BNCT) system and compared the result with that calculated by Monte Carlo simulation. The light distribution was measured in a black box using a cooled charge-coupled device (CCD) camera during irradiation of neutrons to water for 5 s from a cyclotron-based clinical BNCT system. In the measured optical image in water, clear light distribution could be observed during neutron beam irradiation. The depth and lateral profiles of the optical images were well-matched with those calculated by simulation for produced Cerenkov-light by the secondary electrons from prompt gamma photons. The simulated Cerenkov-light was nearly identical to that of the dose for prompt gamma photons. We conclude that the optical imaging of a neutron beam is possible and that it might be used for the dose distribution measurements of prompt gamma photons produced by the nuclear interactions between neutrons and water in addition to the gamma photons from the port and collimator.

检测切伦科夫光或水的发光的光学成像是一种很有前途的方法来测量放射治疗中的剂量分布，因为它能够在很短的测量时间内提供高分辨率的图像。然而，目前尚不清楚水中中子束是否可以进行光学成像。虽然中子在水中不发光，但中子与水相互作用产生的瞬发伽马光子或质子可能会发光。为了阐明这一点，我们测量了硼中子俘获疗法 (BNCT) 系统在照射中子束期间水中的光分布，并将结果与​​蒙特卡罗模拟计算的结果进行了比较。在基于回旋加速器的临床 BNCT 系统将中子照射到水中 5 秒期间，使用冷却电荷耦合器件 (CCD) 相机在黑匣子中测量光分布。在水中测量的光学图像中，在中子束照射过程中可以观察到清晰的光分布。光学图像的深度和横向轮廓与通过模拟由瞬发伽马光子的二次电子产生的切伦科夫光计算的那些很好地匹配。模拟的切伦科夫光与瞬发伽马光子的剂量几乎相同。