Biological Dosimetry Intercomparison Exercise: An Evaluation of Triage and Routine Mode Results by Robust Methods

Abstract

Well-defined protocols and quality management standards are indispensable for biological dosimetry laboratories. Participation in periodic proficiency testing by interlaboratory comparisons is also required. This harmonization is essential if a cooperative network is used to respond to a mass casualty event. Here we present an international intercomparison based on dicentric chromosome analysis for dose assessment performed in the framework of the IAEA Regional Latin American RLA/9/054 Project. The exercise involved 14 laboratories, 8 from Latin America and 6 from Europe. The performance of each laboratory and the reproducibility of the exercise were evaluated using robust methods described in ISO standards. The study was based on the analysis of slides from samples irradiated with 0.75 (DI) and 2.5 Gy (DII). Laboratories were required to score the frequency of dicentrics and convert them to estimated doses, using their own dose-effect curves, after the analysis of 50 or 100 cells (triage mode) and after conventional scoring of 500 cells or 100 dicentrics. In the conntional scoring, at both doses, all reported frequencies were considered as satisfactory, and two reported doses were considered as questionable. The analysis of the data dispersion among the dicentric frequencies and among doses indicated a better reproducibility for estimated doses (15.6% for DI and 8.8% for DII) than for frequencies (24.4% for DI and 11.4% for DII), expressed by the coefficient of variation. In the two triage modes, although robust analysis classified some reported frequencies or doses as unsatisfactory or questionable, all estimated doses were in agreement with the accepted error of ±0.5 Gy. However, at the DI dose and for 50 scored cells, 5 out of the 14 reported confidence intervals that included zero dose and could be interpreted as false negatives. This improved with 100 cells, where only one confidence interval included zero dose. At the DII dose, all estimations fell within ±0.5 Gy of the reference dose interval. The results obtained in this triage exercise indicated that it is better to report doses than frequencies. Overall, in both triage and conventional scoring modes, the laboratory performances were satisfactory for mutual cooperation purposes. These data reinforce the view that collaborative networking in the case of a mass casualty event can be successful.

Triage biodosimetry using centromeric/telomeric PNA probes and Giemsa staining to score dicentrics or excess fragments in non-stimulated lymphocyte prematurely condensed chromosomes

“…Specifically, the interpolation of the frequency of dicentrics scored at metaphase to a pre-established dose-effect calibration curve is considered as the «gold standard» method for biological dosimetry that may be also applied for triage biodosimetry in case of a mass-casualty event [29][30][31]. At present, it is the most validated and widely used method for dose assessment and has been proved to be a very useful biodosimetry tool for acute, protracted, or partial-body exposure [32].…”

Integration of new biological and physical retrospective dosimetry methods into EU emergency response plans – joint RENEB and EURADOS inter-laboratory comparisons

“…The ISO standard for proficiency testing through inter-laboratory comparisons 13528 (ISO 2005) recommends a number of methods for comparing results from two or more laboratories. The robust z-test has previously been usefully applied in biodosimetry (Di Giorgio et al 2011;Wilkins et al 2015) and thus is used again here. The results, which are presented in Table 2, demonstrate satisfactory agreement across the laboratories for the vast majority of the data.…”

The harmonization process to set up and maintain an operational biological and physical retrospective dosimetry network: QA QM applied to the RENEB network

“…It is therefore important to fix the adapted criteria for inter-comparison analysis as it can have an impact on the conclusion of the proficiency of a laboratory. Based on ISO 13528 (ISO 13528 2005), the Z-score has been first used in Di Giorgio's publication (Di Giorgio et al 2011). However, this is not the only parameter to take into account.…”