The specific advantages of ion beams for application in tumor therapy are attributed to their different macroscopic and microscopic energy deposition pattern as compared to conventional photon radiation. On the macroscopic scale, the inverted dose profile with a Bragg peak and small lateral scattering allow a better conformation of the dose to the tumor. On the microscopic scale, the localized energy deposition around the trajectory of the particles leads to an enhanced biological effectiveness, typically expressed in terms of the relative biological effectiveness (RBE). Experimental investigations reveal complex dependencies of RBE on many physical and biological parameters, as e.g., ion species, dose, position in the field and cell or tissue type. In order to complement the experimental work, different approaches are used for the characterization of the specific physical and biological properties of ion beams. In a set of two papers, which are linked by activities within a European HORIZON 2020 project about nuclear science and application (ENSAR2), we describe recent developments in two fields playing a key role in characterizing the increased biological effectiveness. These comprise the biophysical modeling of RBE and the microdosimetric measurements in complex radiation fields. This first paper gives a brief introduction into these fields and then focuses on aspects of biophysical modeling of RBE, specifically on semi-empirical approaches that are currently used in treatment planning for ion beam therapy. It summarizes the status and recent developments of the Local Effect Model (LEM) and its conceptual framework and shows examples of model validation using recent experimental data. The model is compared to other approaches, e.g., to the Microdosimetric-Kinetic Model (MKM), that builds the bridge to the experimental microdosimetric work.

与传统的光子辐射相比，离子束在肿瘤治疗中的特殊优势归因于其不同的宏观和微观能量沉积模式。在宏观尺度上，具有布拉格峰和小的横向散射的反向剂量分布可以使剂量更好地适应肿瘤。在微观尺度上，围绕粒子轨迹的局部能量沉积导致增强的生物有效性，通常以相对生物有效性（RBE）表示。实验研究揭示了RBE对许多物理和生物学参数的复杂依赖性，例如离子种类，剂量，在野外的位置以及细胞或组织的类型。为了补充实验工作，使用不同的方法来表征离子束的特定物理和生物学特性。在一套由欧洲HORIZON 2020项目有关核科学和应用（ENSAR2）的活动所链接的两篇论文中，我们描述了两个领域的最新进展，这些进展在表征提高的生物有效性方面起着关键作用。这些包括RBE的生物物理建模和复杂辐射场中的微剂量测量。第一篇论文简要介绍了这些领域，然后重点介绍了RBE的生物物理模型，尤其是离子束治疗计划中目前使用的半经验方法。它总结了局部效应模型（LEM）及其概念框架的现状和最新发展，并展示了使用最新实验数据进行模型验证的示例。将该模型与其他方法进行比较，例如与微剂量动力学模型（MKM）进行比较，后者建立了通往实验微剂量工作的桥梁。