Many experimental studies are carried out to compare biological effectiveness of high dose rate (HDR) with that of low dose rate (LDR). The rational for this is the uncertainty regarding the value of the dose rate effectiveness factor (DREF) used in radiological protection. While a LDR is defined as 0.1 mGy/min or lower, anything above that is seen as HDR. In cell and animal experiments, a dose rate around 1 Gy/min is usually used as representative for HDR. However, atomic bomb survivors, the reference cohort for radiological protection, were exposed to tens of Gy/min. The important question is whether gamma radiation delivered at very high dose rate (VHDR—several Gy/min) is more effective in inducing DNA damage than that delivered at HDR. The aim of this investigation was to compare the biological effectiveness of gamma radiation delivered at VHDR (8.25 Gy/min) with that of HDR (0.38 Gy/min or 0.79 Gy/min). Experiments were carried out with human peripheral mononuclear cells (PBMC) and the human osteosarcoma cell line U2OS. Endpoints related to DNA damage response were analysed. The results show that in PBMC, VHDR is more effective than HDR in inducing gene expression and micronuclei. In U2OS cells, the repair of 53BP1 foci was delayed after VHDR indicating a higher level of damage complexity, but no VHDR effect was observed at the level of micronuclei and clonogenic cell survival. We suggest that the DREF value may be underestimated when the biological effectiveness of HDR and LDR is compared.

进行了许多实验研究来比较高剂量率（HDR）和低剂量率（LDR）的生物有效性。其原因是放射防护中使用的剂量率有效性因子（DREF）值的不确定性。虽然 LDR 定义为 0.1 mGy/min 或更低，但高于该值的任何值都被视为 HDR。在细胞和动物实验中，通常使用 1 Gy/min 左右的剂量率作为 HDR 的代表。然而，原子弹幸存者（放射防护的参考群体）却暴露在数十戈瑞/分钟的辐射下。重要的问题是以极高剂量率（VHDR——几戈瑞/分钟）提供的伽马辐射是否比 HDR 提供的伽马辐射更有效地诱导 DNA 损伤。本研究的目的是比较 VHDR（8.25 Gy/min）和 HDR（0.38 Gy/min 或 0.79 Gy/min）伽马辐射的生物有效性。使用人外周单核细胞 (PBMC) 和人骨肉瘤细胞系 U2OS 进行实验。分析了与 DNA 损伤反应相关的终点。结果表明，在PBMC中，VHDR在诱导基因表达和微核方面比HDR更有效。在U2OS细胞中，VHDR后53BP1病灶的修复被延迟，表明损伤复杂性更高，但在微核和克隆细胞存活水平上没有观察到VHDR效应。我们认为，当比较 HDR 和 LDR 的生物学有效性时，DREF 值可能被低估。