RENEB Inter-Laboratory Comparison 2021: Inter-Assay Comparison of Eight Dosimetry Assays

LBDNet inter-laboratory comparison at high doses of ionizing radiation using the dicentric plus caffeine assay

PURPOSE

To assess the performance of the LBDNet laboratories in estimating dose over 5 Gy of ionizing radiation using the dicentric chromosome plus caffeine assay.

MATERIALS AND METHODS

Dose-response curve fitting: Peripheral blood was irradiated in vitro between 5 and 25 Gy. Then, the DC plus caffeine assay was carried out. Thirteen laboratories received and analyzed metaphase images. The linear dose-response curve was fitted for each laboratory. Dose estimation was performed analyzing coded metaphase images from three different irradiated samples (7.5, 15, 20 Gy) and using the fitted curve from every laboratory.

RESULTS

The dose estimation accuracy was within the expected dose ranges. The 76.9%, 84.6% and 69.2% of the estimated doses fell into the ± 20% of the true radiation dose. The 92.3%, 92.3%, and 61.5% of the 95% of the confidence interval of the estimated doses included the true radiation dose. The trueness was 0.9%, 4.4% and 9.6%. The Coefficients of Variation of the estimated doses were 14.5%, 16.1% and 17.8%. Results from only one laboratory were deemed questionable for dose estimation, based on the Z-score derived from robust methods.

CONCLUSION

The intercomparison study yielded satisfactory results; however, dose estimation accuracy tended to decrease, and variability between laboratory results increased as the dose level rose.

In silico analysis of radiation-induced double-strand breaks by internal ex vivo irradiation of lymphocytes for 45 alpha- and beta/gamma-emitting radionuclides

BACKGROUND

The aim of this study is to evaluate the induction of DNA damage by 45 radionuclides, including those used in medical applications and others relevant to radiation protection. The research focuses on understanding the differential effects of irradiating lymphocytes with beta/gamma- and alpha-emitting radionuclides using Monte Carlo simulations. A validated Monte Carlo simulation model was used to assess radiation-induced DNA damage in lymphocytes. The model integrates GATE for macroscopic radiation transport and Geant4-DNA for microscopic simulations at the cellular level. For the study, 45 radionuclides were selected and their S-values and DNA double-strand break (DSB) induction were investigated. For beta- and gamma-emitting radionuclides, DSBs per cell per mGy were quantified, while for alpha-emitters, alpha tracks per cell per mGy, DSBs per cell per mGy, and DSBs per micrometer of alpha track were calculated.

RESULT

For beta/gamma emitters, the lowest number of DSBs was observed with 125I at 0.006 ± 0.003 DSBs·cell⁻¹·mGy⁻¹, while 99mTc had the highest at approximately 0.015 ± 0.005 DSBs·cell⁻¹·mGy⁻¹. The S-value for lymphocyte nuclei ranked from 0.91 ± 0.14 mGy∙h⁻¹∙MBq⁻¹ (63Ni) and 1.06 ± 0.15 mGy∙h⁻¹∙MBq⁻¹ (125I) to 61.83 ± 1.17 mGy∙h⁻¹∙MBq⁻¹ (90Sr). For alpha-emitting radionuclides, 213Bi produced 0.0677 ± 0.0005 DSB·cell⁻¹·mGy⁻¹ while 232Th yielded 0.0914 ± 0.0004 DSB·cell⁻¹·mGy⁻¹. The DSB linear density for alpha tracks ranged from 7.4 ± 0.1 DSBs/µm for 252Cf to 16.8 ± 0.1 DSBs/µm for 232Th. The S-values for lymphocyte nuclei for alpha emitters varied, from 232Th (0.29 ± 0.21 Gy∙h⁻¹∙MBq⁻¹) to 227Th having the highest at 2.22 ± 0.16 Gy∙h⁻¹∙MBq⁻¹, due to cumulative energy deposition.

CONCLUSIONS

Differences were observed in DNA damage induced by beta/gamma- and alpha-emitting radionuclides. High-energy beta emitters induced DSBs similarly to gamma emitters, but with greater fluctuations in low-energy beta and gamma emitters due to heterogeneous energy deposition and varying interaction probabilities at the cellular level. This study highlights that long half-life alpha-emitting radionuclides may cause more extensive DNA damage due to their higher LET. This work provides a comprehensive S-values database for future experimental studies on radiation-induced DNA damage in lymphocytes.

Intercomparison exercise on electron paramagnetic resonance dosimetry in sorbitol

This paper presents the results of the first intercomparison exercise on Electron Paramagnetic Resonance (EPR) dosimetry using sorbitol, where the performance parameters of sorbitol as dosimetric material were evaluated by three independent participants. Each participant was asked to determine a calibration curve using a set of sorbitol powder samples irradiated to four different doses (1.00, 2.50, 5.00, and 10.00 Gy of air kerma). The calibration doses were known to the participants, who were asked to measure each sample three times, and to report the EPR signal response, the mass of aliquots measured, and the parameters of EPR signal acquisition and signal evaluation. Critical dose and detection limit were calculated based on the calibration-curve parameters obtained by each participant. The mean values of the detection limit and average critical dose were found to be 802 ± 148 mGy and 411 ± 77 mGy, respectively. These values were compared with those of for alanine, glass and tooth enamel. The participants were also provided with four blind samples irradiated to four unknown doses, and their reported doses were compared with the delivered doses and performance quotient was calculated for each participant. The findings indicate that sorbitol is a promising candidate for accidental and retrospective dosimetry.

DNA Damage and Repair in PBMCs after Internal Ex Vivo Irradiation with [223Ra]RaCl2 and [177Lu]LuCl3 Mixtures

The combination of high and low LET radionuclides has been tested in several patient studies to improve treatment response. Radionuclide mixtures can also be released in nuclear power plant accidents or nuclear bomb deployment. This study investigated the DNA damage response and DNA double-strand break (DSB) repair in peripheral blood mononuclear cells (PBMCs) after internal exposure of blood samples of 10 healthy volunteers to either no radiation (baseline) or different radionuclide mixtures of the α- and β-emitters [223Ra]RaCl2 and [177Lu]LuCl3, i.e., 25 mGy/75 mGy, 50 mGy/50 mGy and 75 mGy/25 mGy, respectively. DSB foci and γ-H2AX α-track enumeration directly after 1 h of exposure or after 4 h or 24 h of repair revealed that radiation-induced foci (RIF) and α-track induction in 100 cells was similar for mixed α/β and pure internal α- or β-irradiation, as were the repair rates for all radiation qualities. In contrast, the fraction of unrepaired RIF (Qβ) in PBMCs after mixed α/β-irradiation (50% 223Ra & 50% 177Lu: Qβ = 0.23 ± 0.10) was significantly elevated relative to pure β-irradiation (50 mGy: Qβ, pure = 0.06 ± 0.02), with a similar trend being noted for all mixtures. This α-dose-dependent increase in persistent foci likely relates to the formation of complex DNA damage that remains difficult to repair.

Calibration curve for radiation dose estimation using FDXR gene expression biodosimetry - premises and pitfalls

PURPOSE

Radiation-induced alterations in gene expression show great promise for dose reconstruction and for severity prediction of acute health effects. Among several genes explored as potential biomarkers, FDXR is widely used due to high upregulation in white blood cells following radiation exposure. Nonetheless, the absence of a standardized protocols for gene expression-based biodosimetry is a notable gap that warrants attention to enhance the accuracy, reproducibility and reliability. The objective of this study was to evaluate the sensitivity of transcriptional biodosimetry to differences in protocols used by different laboratories and establish guidelines for the calculation of calibration curve using FDXR expression data.

MATERIAL AND METHODS

Two sets of irradiated blood samples generated during RENEB exercise were used. The first included samples irradiated with known doses including: 0, 0.25, 0.5, 1, 2, 3 and 4 Gy. The second set consisted of three 'blind' samples irradiated with 1.8 Gy, 0.4 Gy and a sham-irradiated sample. After irradiation, samples were incubated at 37 °C over 24 h and sent to participating laboratories, where RNA isolation and FDXR expression analysis by qPCR were performed using sets of primers/probes and reference genes specific for each laboratory. Calibration curves based on FDXR expression data were generated using non-linear and linear regression and used for dose estimation of 'blind' samples.

RESULTS

Dose estimates for sham-irradiated sample (0.020-0.024 Gy) and sample irradiated with 0.4 Gy (0.369-0.381 Gy) showed remarkable consistency across all laboratories, closely approximating the true doses regardless variation in primers/probes and reference genes used. For sample irradiated with 1.8 Gy the dose estimates were less precise (1.198-2.011 Gy) but remained within an acceptable margin for triage within the context of high dose range.

CONCLUSION

Methodological differences in reference genes and primers/probes used for FDXR expression measurement do not have a significant impact on the dose estimates generated, provided that all reference genes performed as expected and the primers/probes target a similar set of transcript variants. The preferred method for constructing a calibration curve based on FDXR expression data involves employing linear regression to establish a function that describes the relationship between the logarithm of absorbed dose and FDXR ΔCt values. However, one should be careful with using non-irradiated sample data as these cannot be accurately represented on a logarithmic scale. A standard curve generated using this approach can give reliable dose estimations in a dose range from 50 mGy to 4 Gy at least.

LBDNet interlaboratory comparison for the dicentric chromosome assay by digitized image analysis applying weighted robust statistical methods

PURPOSE

This interlaboratory comparison was conducted to evaluate the performance of the Latin-American Biodosimetry Network (LBDNet) in analyzing digitized images for scoring dicentric chromosomes from in vitro irradiated blood samples. The exercise also assessed the use of weighted robust algorithms to compensate the uneven expertise among the participating laboratories.

METHODS

Three sets of coded images obtained through the dicentric chromosome assay from blood samples irradiated at 1.5 Gy (sample A) and 4 Gy (sample B), as well as a non-irradiated whole blood sample (sample C), were shared among LBDNet laboratories. The images were captured using the Metafer4 platform coupled with the AutoCapt module. The laboratories were requested to perform triage scoring, conventional scoring, and dose estimation. The dose estimation was carried out using either their laboratory calibration curve or a common calibration curve. A comparative statistical analysis was conducted using a weighted robust Hampel algorithm and z score to compensate for uneven expertise in dicentric analysis and dose assessment among all laboratories.

RESULTS

Out of twelve laboratories, one had unsatisfactory estimated doses at 0 Gy, and two had unsatisfactory estimated doses at 1.5 Gy when using their own calibration curve and triage scoring mode. However, all doses were satisfactory at 4 Gy. Six laboratories had estimated doses within 95% uncertainty limits at 0 Gy, seven at 1.5 Gy, and four at 4 Gy. While the mean dose for sample C was significantly biased using robust algorithms, applying weights to compensate for the laboratory's analysis expertise reduced the bias by half. The bias from delivered doses was only notable for sample C. Using the common calibration curve for dose estimation reduced the standard deviation (s*) estimated by robust methods for all three samples.

CONCLUSIONS

The results underscore the significance of performing interlaboratory comparison exercises that involve digitized and electronically transmitted images, even when analyzing non-irradiated samples. In situations where the participating laboratories possess different levels of proficiency, it may prove essential to employ weighted robust algorithms to achieve precise outcomes.

Modelling the In Vivo and Ex Vivo DNA Damage Response after Internal Irradiation of Blood from Patients with Thyroid Cancer

This work reports on a model that describes patient-specific absorbed dose-dependent DNA damage response in peripheral blood mononuclear cells of thyroid cancer patients during radioiodine therapy and compares the results with the ex vivo DNA damage response in these patients. Blood samples of 18 patients (nine time points up to 168 h post-administration) were analyzed for radiation-induced γ-H2AX + 53BP1 DNA double-strand break foci (RIF). A linear one-compartment model described the absorbed dose-dependent time course of RIF (Parameters: c characterizes DSB damage induction; k1 and k2 are rate constants describing fast and slow repair). The rate constants were compared to ex vivo repair rates. A total of 14 patient datasets could be analyzed; c ranged from 0.012 to 0.109 mGy-1, k2 from 0 to 0.04 h-1. On average, 96% of the damage is repaired quickly with k1 (range: 0.19-3.03 h-1). Two patient subgroups were distinguished by k1-values (n = 6, k1 > 1.1 h-1; n = 8, k1 < 0.6 h-1). A weak correlation with patient age was observed. While induction of RIF was similar among ex vivo and in vivo, the respective repair rates failed to correlate. The lack of correlation between in vivo and ex vivo repair rates and the applicability of the model to other therapies will be addressed in further studies.

Lessons on harmonization of scoring criteria for dicentric chromosome assay in South Korea

PURPOSE

Networking with other biodosimetry laboratories is necessary to assess the radiation exposure of many individuals in large-scale radiological accidents. The Korea biodosimetry network, K-BioDos, prepared harmonized scoring guidelines for dicentric chromosome assay to obtain homogeneous results within the network and investigated the efficiency of the guidelines.

MATERIALS AND METHODS

Three laboratories in K-BioDos harmonized the scoring guidelines for dicentric chromosome assay. The results of scoring dicentric chromosomes using the harmonized scoring guidelines were compared with the laboratories' results using their own methods. Feedback was collected from the scorers following the three intercomparison exercises in 3 consecutive years.

RESULTS

K-BioDos members showed comparable capacity to score dicentrics in the three exercises. However, the results of the K-BioDos guidelines showed no significant improvement over those of the scorers' own methods. According to the scorers, our harmonized guidelines led to more rejected metaphases and ultimately decreased the number of scorable metaphases compared with their own methods. Moreover, the scoring time was sometimes longer with the K-BioDos protocol because some scorers were not yet familiar with the guidelines, though most scorers reported that the time decreased or was unchanged. These challenges may cause low adherence to the guidelines. Most scorers expressed willingness to use the guidelines to select scorable metaphases or identify dicentrics for other biodosimetry works, whereas one did not want to use it due to the difference from their calibration curves.

CONCLUSIONS

We identified potential resistance to following the harmonized guidelines and received requests for more detailed methods. Our findings suggest that the harmonized criteria should be continually updated, and education and training should be provided for all scorers. These changes could allow members within the biodosimetry network to successfully collaborate and support each other in large-scale radiological accidents.