Significance: Optical imaging of Cherenkov emission during radiation therapy could be used to verify dose delivery in real-time if a more comprehensive quantitative understanding of the factors affecting emission intensity could be developed. Aim: This study aims to explore the change in diffuse Cherenkov emission intensity with x-ray beam energy from irradiated tissue, both theoretically and experimentally. Approach: Derivation of the emitted Cherenkov signal was achieved using diffusion theory, and experimental studies with 6 to 18 MV energy x-rays were performed in tissue phantoms to confirm the model predictions as related to the radiation build-up factor with depth into tissue. Results: Irradiation at lower x-ray energies results in a greater surface dose and higher build-up slope, which results in a ∼46 % greater diffusely emitted Cherenkov signal per unit dose at 6 MV relative to 18 MV x-rays. However, this phenomenon competes with a decrease in signal from less Cherenkov photons being generated at lower energies, a ∼44 % reduction at 6 versus 18 MV. The result is an emitted Cherenkov signal that is nearly constant with beam energy. Conclusions: This study explains why the observed Cherenkov emission from tissue is not a strong function of beam energy, despite the known strong correlation between Cherenkov intensity and particle energy in the absence of build-up and scattering effects.

中文翻译：

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来自组织中外部光束辐射积累的漫切伦科夫光发射的估计

意义：如果可以对影响发射强度的因素进行更全面的定量理解，则放射治疗期间切伦科夫发射的光学成像可用于实时验证剂量输送。目的：本研究旨在从理论和实验两方面探索漫切伦科夫发射强度随受照射组织的 X 射线束能量的变化。方法：使用扩散理论获得发射的 Cherenkov 信号，并在组织体模中使用 6 到 18 MV 能量 X 射线进行实验研究，以确认模型预测与辐射积累因子与进入组织的深度有关。结果：以较低的 X 射线能量照射会导致更大的表面剂量和更高的堆积斜率，与 18 MV X 射线相比，这导致在 6 MV 下每单位剂量的漫射 Cherenkov 信号大 46%。然而，这种现象与由于在较低能量下产生的切伦科夫光子较少而导致的信号减少相矛盾，在 6 与 18 MV 时减少了约 44%。结果是发射的 Cherenkov 信号与束能量几乎恒定。结论：这项研究解释了为什么观察到的来自组织的 Cherenkov 发射不是束能量的强函数，尽管在没有累积和散射效应的情况下，Cherenkov 强度和粒子能量之间存在已知的强相关性。结果是发射的 Cherenkov 信号与束能量几乎恒定。结论：这项研究解释了为什么观察到的来自组织的 Cherenkov 发射不是束能量的强函数，尽管在没有累积和散射效应的情况下，Cherenkov 强度和粒子能量之间存在已知的强相关性。结果是发射的 Cherenkov 信号与束能量几乎恒定。结论：这项研究解释了为什么观察到的来自组织的 Cherenkov 发射不是束能量的强函数，尽管在没有累积和散射效应的情况下，Cherenkov 强度和粒子能量之间存在已知的强相关性。