Supplementary Material for: International comparison exercise for biological dosimetry after exposures with neutrons performed at two irradiation facilities as part of the BALANCE project

In the case of a radiological or nuclear event, biological dosimetry can be an important tool to support clinical decision-making. During a nuclear event, individuals might be exposed to a mixed field of neutrons and photons. The composition of the field and the neutron energy spectrum influence the degree of damage to the chromosomes. During the transatlantic BALANCE project, an exposure similar to a Hiroshima-like device at a distance of 1.5 km from the epicenter was simulated and biological dosimetry based on dicentric chromosomes was performed to evaluate the participants ability to discover unknown doses and to test the influence of differences in neutron spectra. In a first step, calibration curves were established by irradiating blood samples with 5 doses in the range of 0 Gy to 4 Gy at two different facilities in Germany (PTB) and USA (CINF). The samples were sent to eight participating laboratories from the RENEB network and dicentric chromosomes were scored by each participant. Next, blood samples were irradiated with 4 blind doses in each of the two facilities and sent to the participants to provide dose estimates based on the established calibration curves. Manual and semi-automatic scoring of dicentric chromosomes were evaluated for their applicability to neutron exposures. Moreover, the biological effectiveness of the neutrons from the two irradiation facilities was compared. The calibration curves from samples irradiated at CINF showed a 1.4 times higher biological effectiveness compared to samples irradiated at PTB. For manual scoring of dicentric chromosomes, the doses of the test samples were mostly successfully resolved based on the calibration curves established during the project. For semi-automatic scoring, the dose estimation for the test samples was less successful. Doses >2 Gy in the calibration curves revealed non-linear associations between dose and dispersion index of the dicentric counts, especially for manual scoring. The differences in the biological effectiveness between the irradiation facilities suggested that the neutron energy spectrum can have a strong impact on the dicentric counts.

在放射或核突发事件中，生物剂量学（biological dosimetry）可作为支撑临床决策的关键工具。核事件发生期间，受照人员可能会暴露于中子与光子混合辐射场中。辐射场的组分与中子能谱会影响染色体的损伤程度。在跨大西洋BALANCE项目中，研究人员模拟了距爆心投影点1.5公里处类似广岛核装置的辐射暴露场景，并开展了基于双着丝粒染色体（dicentric chromosomes）的生物剂量学分析，以评估参与者识别未知受照剂量的能力，同时检验中子能谱差异所带来的影响。研究首先在德国PTB与美国CINF两家不同的辐照机构中，以0 Gy至4 Gy范围内的5个梯度剂量对血液样本进行辐照，以此建立剂量-效应校准曲线。随后将样本寄送至RENEB网络旗下的8家参与实验室，由各参与方对双着丝粒染色体进行计数。继而，两家机构分别以4个盲法剂量对血液样本进行辐照，并将样本寄送给参与方，要求其基于已建立的校准曲线开展剂量估算。研究对双着丝粒染色体的人工计数与半自动计数两种方式在中子辐照场景下的适用性进行了评估。此外，还对比了两家辐照机构产生的中子的生物有效性。相较于在PTB辐照的样本，CINF辐照样本对应的校准曲线显示其中子生物有效性高出1.4倍。针对双着丝粒染色体人工计数方式，基于本项目建立的校准曲线，多数待测样本的受照剂量可被准确估算。而采用半自动计数方式时，待测样本的剂量估算准确率相对较低。在校准曲线中，当受照剂量大于2 Gy时，剂量与双着丝粒计数离散指数之间呈现非线性关联，该现象在人工计数场景中尤为显著。两家辐照机构的中子生物有效性存在差异，这表明中子能谱对双着丝粒染色体计数具有显著影响。