Inter-laboratory comparison of gene expression biodosimetry for protracted radiation exposures as part of the RENEB and EURADOS WG10 2019 exercise

Abstract

Large-scale radiation emergency scenarios involving protracted low dose rate radiation exposure (e.g. a hidden radioactive source in a train) necessitate the development of high throughput methods for providing rapid individual dose estimates. During the RENEB (Running the European Network of Biodosimetry) 2019 exercise, four EDTA-blood samples were exposed to an Iridium-192 source (1.36 TBq, Tech-Ops 880 Sentinal) at varying distances and geometries. This resulted in protracted doses ranging between 0.2 and 2.4 Gy using dose rates of 1.5–40 mGy/min and exposure times of 1 or 2.5 h. Blood samples were exposed in thermo bottles that maintained temperatures between 39 and 27.7 °C. After exposure, EDTA-blood samples were transferred into PAXGene tubes to preserve RNA. RNA was isolated in one laboratory and aliquots of four blinded RNA were sent to another five teams for dose estimation based on gene expression changes. Using an X-ray machine, samples for two calibration curves (first: constant dose rate of 8.3 mGy/min and 0.5–8 h varying exposure times; second: varying dose rates of 0.5–8.3 mGy/min and 4 h exposure time) were generated for distribution. Assays were run in each laboratory according to locally established protocols using either a microarray platform (one team) or quantitative real-time PCR (qRT-PCR, five teams). The qRT-PCR measurements were highly reproducible with coefficient of variation below 15% in ≥ 75% of measurements resulting in reported dose estimates ranging between 0 and 0.5 Gy in all samples and in all laboratories. Up to twofold reductions in RNA copy numbers per degree Celsius relative to 37 °C were observed. However, when irradiating independent samples equivalent to the blinded samples but increasing the combined exposure and incubation time to 4 h at 37 °C, expected gene expression changes corresponding to the absorbed doses were observed. Clearly, time and an optimal temperature of 37 °C must be allowed for the biological response to manifest as gene expression changes prior to running the gene expression assay. In conclusion, dose reconstructions based on gene expression measurements are highly reproducible across different techniques, protocols and laboratories. Even a radiation dose of 0.25 Gy protracted over 4 h (1 mGy/min) can be identified. These results demonstrate the importance of the incubation conditions and time span between radiation exposure and measurements of gene expression changes when using this method in a field exercise or real emergency situation.

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“…Regular quality-controlled inter-laboratory comparisons (ILCs) are important to allow the comparison of laboratories performance and to identify needs to optimize international networking and the workflows of the participants for preparedness to future RN events. ILCs simulating various real-life exposure situations are regularly performed in the frame of RENEB to validate and improve the procedures of the participants for various assays (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28).…”

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“…While biodosimetry using traditional cytogenetic assays is useful for dose assessments following accidental exposure to ionizing radiation, the field of biodosimetry has advanced significantly with expansion into the fields of genomics, proteomics, metabolomics, and transcriptomics [ 112 , 113 , 114 , 115 ]. However, advances in the assessment of radiation exposure using those approaches have more relevance to clinical applications for patients undergoing radiation therapy.…”

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“…Within the RENEB network, regular inter-laboratory comparison exercises have been organized for harmonization and training as well as to maintain the preparedness for large-scale emergency situations, using a broad variety of biodosimetric assays (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19).…”