Kalholm Fredrik, Grzanka Leszek, Traneus Erik, Bassler Niels
Medical Radiation Physics, Dept. of Physics, Stockholm University, Stockholm, Sweden; Department of Oncology and Pathology, Medical Radiation Physics, Karolinska Institutet, Stockholm, Sweden.
Institute of Nuclear Physics Polish Academy of Sciences, Krakow, Poland.
Radiother Oncol. 2021 Aug;161:211-221. doi: 10.1016/j.radonc.2021.04.007. Epub 2021 Apr 21.
Linear Energy Transfer (LET) is widely used to express the radiation quality of ion beams, when characterizing the biological effectiveness. However, averaged LET may be defined in multiple ways, and the chosen definition may impact the resulting reported value. We review averaged LET definitions found in the literature, and quantify which impact using these various definitions have for different reference setups. We recorded the averaged LET definitions used in 354 publications quantifying the relative biological effectiveness (RBE) of hadronic beams, and investigated how these various definitions impact the reported averaged LET using a Monte Carlo particle transport code. We find that the kind of averaged LET being applied is, generally, poorly defined. Some definitions of averaged LET may influence the reported averaged LET values up to an order of magnitude. For publications involving protons, most applied dose averaged LET when reporting RBE. The absence of what target medium is used and what secondary particles are included further contributes to an ill-defined averaged LET. We also found evidence of inconsistent usage of averaged LET definitions when deriving LET-based RBE models. To conclude, due to commonly ill-defined averaged LET and to the inherent problems of LET-based RBE models, averaged LET may only be used as a coarse indicator of radiation quality. We propose a more rigorous way of reporting LET values, and suggest that ideally the entire particle fluence spectra should be recorded and provided for future RBE studies, from which any type of averaged LET (or other quantities) may be inferred.
在表征生物效应时，线能量转移（LET）被广泛用于表达离子束的辐射质量。然而，平均LET可以用多种方式定义，所选择的定义可能会影响最终报告的值。我们回顾了文献中发现的平均LET定义，并量化了使用这些不同定义对不同参考设置的影响。我们记录了354篇量化强子束相对生物效应（RBE）的出版物中使用的平均LET定义，并使用蒙特卡罗粒子输运代码研究了这些不同定义如何影响报告的平均LET。我们发现，所应用的平均LET类型通常定义不明确。一些平均LET的定义可能会使报告的平均LET值相差一个数量级。对于涉及质子的出版物，在报告RBE时大多应用剂量平均LET。未说明使用何种靶介质以及包含哪些次级粒子进一步导致了平均LET定义不明确。我们还发现，在推导基于LET的RBE模型时，存在平均LET定义使用不一致的证据。总之，由于平均LET通常定义不明确以及基于LET的RBE模型存在固有问题，平均LET可能仅用作辐射质量的粗略指标。我们提出了一种更严格的报告LET值的方法，并建议理想情况下应记录并提供整个粒子注量谱，以供未来的RBE研究使用，从中可以推断出任何类型的平均LET（或其他量）。
