Chromosome aberrations as biomarkers of radiation exposure: modelling basic mechanisms.

The space radiation environment is a mixed field consisting of different particles having different energies,
including high charge and energy (HZE) ions. Conventional measurements of absorbed doses may not be sufficient
to completely characterise the radiation field and perform reliable estimates of health risks. Biological dosimetry,
based on the observation of specific radiation-induced endpoints (typically chromosome aberrations), can be a
helpful approach in case of monitored exposure to space radiation or other mixed fields, as well as in case of
accidental exposure. Furthermore, various ratios of aberrations (e.g. dicentric chromosomes to centric rings and
complex exchanges to simple exchanges) have been suggested as possible fingerprints of radiation quality,
although all of them have been subjected to some criticisms. In this context a mechanistic model and a Monte Carlo
code for the simulation of chromosome aberration induction were developed. The model, able to provide doseresponses
for different aberrations (e.g. dicentrics, rings, fragments, mu&cations, insertions and other complex
exchanges), was further developed to assess the dependence of various ratios of aberrations on radiation quality.
The predictions of the model were compared with available data, whose experimental conditions were faithfully
reproduced. Particular attention was devoted to the scoring criteria adopted in different laboratories and to possible
biases introduced by interphase death and mitotic delay. This latter aspect was investigated by taking into account
both metaphase data and data obtained with Premature Chromosome Condensation (PCC).