Abstract A nano-microdosimetric tissue-equivalent proportional counter (TEPC) capable of measuring microdosimetric spectra of ionizing radiation in the range 500–25 nm was designed, constructed and deeply characterized in order to fill the gap between nanodosimetry and experimental microdosimetry. This work describes the first microdosimetric characterization at nanometric level of a 195.2 MeV/u carbon ion beam available at CNAO (National Centre for Oncological Hadron Therapy). The detector was properly placed at different depths in PMMA phantom across the depth-dose profile of the primary beam for measuring microdosimetric distributions for different simulated site sizes down to 25 nm at different depths. The acquired spectra show that this TEPC is capable of reproducing the beam slowing down, showing a shift towards higher lineal energies as the primary particles slow-down. Moreover, the distributions at different simulated site sizes for the same depth are influenced by secondary electrons: smaller site size spectra exhibit a shift towards higher lineal energies as the site decreases, while this is not the case for more distal positions, where the edge of the spectra is almost independent of the simulated site size. Monte Carlo simulations performed with the FLUKA code show a good agreement with the experimental results obtained in the present paper.

中文翻译：

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CNAO 治疗性碳离子束的纳米微剂量表征

摘要 为了填补纳米剂量学与实验微剂量学之间的空白，设计、构建并深入表征了一种能够测量500-25 nm范围内电离辐射微剂量谱的纳米微剂量组织等效正比计数器（TEPC）。这项工作描述了 CNAO（国家肿瘤强子治疗中心）提供的 195.2 MeV/u 碳离子束在纳米级的首次微剂量表征。探测器被正确放置在 PMMA 体模的不同深度，跨越主光束的深度剂量分布，用于测量不同深度的不同模拟部位尺寸的微剂量分布，低至 25 nm。获得的光谱表明该 TEPC 能够再现减速的光束，随着初级粒子减速，显示出向更高线能的转变。此外，相同深度的不同模拟位点尺寸的分布受二次电子的影响：随着位点的减少，更小的位点尺寸谱表现出向更高的线能量移动，而对于更远的位置则不是这种情况，其中的边缘光谱几乎与模拟站点的大小无关。使用 FLUKA 代码执行的蒙特卡罗模拟与本文获得的实验结果非常吻合。而对于更远的位置则不是这种情况，其中光谱的边缘几乎与模拟站点的大小无关。使用 FLUKA 代码执行的蒙特卡罗模拟与本文获得的实验结果非常吻合。而对于更远的位置则不是这种情况，其中光谱的边缘几乎与模拟站点的大小无关。使用 FLUKA 代码执行的蒙特卡罗模拟与本文获得的实验结果非常吻合。