Institute for Applied Physics and Measurement Technology, Universität Der Bundeswehr München, Neubiberg, Germany.
Department of Radiation Dosimetry, Nuclear Physics Institute CAS, Prague, Czech Republic.
Sci Rep. 2022 Jan 25;12(1):1305. doi: 10.1038/s41598-022-05413-6.
The human body is constantly exposed to ionizing radiation of different qualities. Especially the exposure to high-LET (linear energy transfer) particles increases due to new tumor therapy methods using e.g. carbon ions. Furthermore, upon radiation accidents, a mixture of radiation of different quality is adding up to human radiation exposure. Finally, long-term space missions such as the mission to mars pose great challenges to the dose assessment an astronaut was exposed to. Currently, DSB counting using γH2AX foci is used as an exact dosimetric measure for individuals. Due to the size of the γH2AX IRIF of ~ 0.6 µm, it is only possible to count DSB when they are separated by this distance. For high-LET particle exposure, the distance of the DSB is too small to be separated and the dose will be underestimated. In this study, we developed a method where it is possible to count DSB which are separated by a distance of ~ 140 nm. We counted the number of ionizing radiation-induced pDNA-PKcs (DNA-PKcs phosphorylated at T2609) foci (size = 140 nm ± 20 nm) in human HeLa cells using STED super-resolution microscopy that has an intrinsic resolution of 100 nm. Irradiation was performed at the ion microprobe SNAKE using high-LET 20 MeV lithium (LET = 116 keV/µm) and 27 MeV carbon ions (LET = 500 keV/µm). pDNA-PKcs foci label all DSB as proven by counterstaining with 53BP1 after low-LET γ-irradiation where separation of individual DSB is in most cases larger than the 53BP1 gross size of about 0.6 µm. Lithium ions produce (1.5 ± 0.1) IRIF/µm track length, for carbon ions (2.2 ± 0.2) IRIF/µm are counted. These values are enhanced by a factor of 2-3 compared to conventional foci counting of high-LET tracks. Comparison of the measurements to PARTRAC simulation data proof the consistency of results. We used these data to develop a measure for dosimetry of high-LET or mixed particle radiation exposure directly in the biological sample. We show that proper dosimetry for radiation up to a LET of 240 keV/µm is possible.
人体不断受到不同质量的电离辐射的照射。特别是由于使用碳离子等新的肿瘤治疗方法，高传能线密度（linear energy transfer，LET）粒子的照射增加了。此外，在辐射事故中，不同质量的辐射混合在一起，增加了人类的辐射暴露。最后，像火星任务这样的长期太空任务对宇航员所受辐射剂量的评估带来了巨大挑战。目前，使用 γH2AX 焦点来计算双链断裂（double-strand breaks，DSB）是个体精确剂量测量的一种方法。由于 γH2AX 免疫荧光焦点（immunofluorescence focus，IRIF）的大小约为 0.6 µm，只有当它们之间的距离达到这个距离时，才能计算 DSB。对于高 LET 粒子照射，DSB 的距离太小，无法分开，从而导致剂量低估。在这项研究中，我们开发了一种方法，可以计算距离约为 140nm 的 DSB。我们使用具有 100nm 固有分辨率的 STED 超分辨率显微镜，在人类 HeLa 细胞中计算了电离辐射诱导的 pDNA-PKcs（在 T2609 处磷酸化的 DNA 依赖性蛋白激酶）焦点的数量（大小= 140nm±20nm）。使用离子微探针 SNAKE 进行照射，使用高 LET 20 MeV 锂（LET=116keV/µm）和 27 MeV 碳离子（LET=500keV/µm）。通过用低 LET γ 射线照射后用 53BP1 进行复染证明，pDNA-PKcs 焦点标记了所有 DSB，因为在大多数情况下，单个 DSB 的分离大于 53BP1 的大约 0.6 µm 的总大小。锂离子产生（1.5±0.1）个 IRIF/µm 轨迹长度，而碳离子则计数（2.2±0.2）个 IRIF/µm。与高 LET 轨迹的传统焦点计数相比，这些值提高了 2-3 倍。将测量值与 PARTRAC 模拟数据进行比较证明了结果的一致性。我们使用这些数据直接在生物样本中开发了一种用于高 LET 或混合粒子辐射暴露的剂量测量方法。我们表明，对于 LET 高达 240keV/µm 的辐射，进行适当的剂量测量是可能的。
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