Triage dose assessment for partial-body exposure: dicentric analysis.

Partial-body biodosimetry is likely to be required after a radiological or nuclear exposure. Clinical signs and symptoms, distribution of dicentrics in circulating blood cells, organ-specific biomarkers, and physical signals in teeth and fingernails all can provide indications of non-homogeneous exposures. Organ specific biomarkers may provide early warning regarding physiological systems at risk after radiation injury. Use of a combination of markers and symptoms will be needed for clinical insights for therapeutic approaches. Analysis of dicentrics, a marker specific for radiation injury, is the "gold standard" of biodosimetry and can reveal partial-body exposures. Automation of sample processing for dicentric analysis can increase throughput with customization of off-the-shelf technologies for cytogenetic sample processing and information management. Automated analysis of the metaphase spreads is currently limited, but improvements are in development. The efforts described here bridge the technological gaps to allow the use of dicentric chromosome assay (DCA) for risk-based stratification of mass casualties. This article summarizes current knowledge on partial-body cytogenetic dose assessment, synthesizing information leading to the proposal of an approach to triage dose prediction in radiation mass casualties that is based on equivalent whole-body doses under partial-body exposure conditions and assesses the validity of using this model. An initial screening using only 20 metaphase spreads per subject can confirm irradiation above 2 Gy. A subsequent increase to 50 metaphases improves dose determination to allow risk stratification for clinical triage. Metaphases evaluated for inhomogeneous distribution of dicentrics can reveal partial-body exposures. The authors tested the validity of this approach in an in vitro model that simulates partial-body irradiation by mixing irradiated and un-irradiated lymphocytes in various proportions. Preliminary results support the notion that this approach will be effective under a range of conditions including some partial-body exposures, but may have limitations with low doses or small proportions of irradiated parts of the body. These studies address an important problem in the diagnosis of partial-body irradiation and dose assessment in mass casualties and propose a solution. However, additional work is needed to fully develop and validate the application of DCA to partial-body exposures.