Research on the applications of microdosimetry to particle therapy is spreading worldwide with a rapid increase of publications in the last years. In order to be able to perform an intercomparison of data acquired with different detectors in different clinical centres it is important to analyse data with a standard procedure. Often microdosimetric spectra are presented with different lower detection thresholds, in relation with different detection sensitivity and noise levels. The purpose of this paper is to analyse the influence of the lower detection threshold on the dose-mean lineal energy values, which are used as an assessment of the average LET of the radiation field. Furthermore, the dose distribution of the lineal energy can be used in combination with biological weighting functions to estimate the biological RBE at different positions along the penetration depths of therapeutic proton or carbon ion beams. Microdosimetric spectra cut at different lower thresholds lead in principle to different RBE values. It was an additional purpose of this work to analyse and discuss this effect both for proton and carbon ion irradiations.

Spectra in proton and carbon ion beams gathered with a miniaturized TEPC developed at the Legnaro National Laboratories of the Italian Institute for Nuclear Physics (LNL-INFN) have been used to perform this study.

Linear extrapolation of the microdosimetric spectra to a common value of 0.01 keV/μm significantly reduces the deviations in the mean values due to different lower thresholds. It is advisable to perform this procedure to have uniformity in data analysis and facilitate the intercomparison of data.

微剂量学在粒子治疗中的应用研究正在世界范围内传播，近年来出版物数量迅速增加。为了能够对不同临床中心的不同探测器采集的数据进行比对，使用标准程序分析数据非常重要。通常，微剂量光谱具有不同的较低检测阈值，与不同的检测灵敏度和噪声水平有关。本文的目的是分析下检测阈值对剂量平均线能量值的影响，这些值被用作辐射场平均 LET 的评估。此外，线性能量的剂量分布可与生物加权函数结合使用，以估计沿治疗质子或碳离子束穿透深度不同位置的生物 RBE。在不同的较低阈值处切割的微剂量光谱原则上会导致不同的 RBE 值。这项工作的另一个目的是分析和讨论这种对质子和碳离子辐射的影响。

由意大利核物理研究所 (LNL-INFN) 的莱格纳罗国家实验室开发的小型化 TEPC 收集的质子和碳离子束中的光谱已用于进行这项研究。

将微剂量光谱线性外推到 0.01 keV/μm 的共同值，显着降低了由于不同下阈值而导致的平均值偏差。建议执行此程序以在数据分析中具有一致性并促进数据的比对。