The issues of low dose and low dose rate exposure of human as well as the acquisition of knowledge on common genetic factors that might determine inter-individual differences in low dose cancer risk are of continuing importance in respect of social/economic policy relating to the industrial and medical uses of ionizing radiation. Furthermore, for risk assessment among people occupationally are being exposed to low and/or high LET radiation, such as astronauts, pilots, stewardess, nuclear power plant workers and patients under radiotherapy treatment, namely children.

In order to emphasis on the acquisition of fundamental knowledge and the development of low dose as well as high dose risk models for low LET radiation (i.e. gamma-rays and X-rays) and high LET radiation (i.e. heavy ions, alpha-particles, neutrons) several biological assays were developed and attempts were made to investigate formation of radiation induced chromosome aberrations and induction of genomic instability in human lymphocytes and fibroblasts: Mechanisms, Kinetics and Spectra were defined.

Fluorescence in situ hybridization (FISH) technique using chromosome, chromosome- arm, chromosome region, centromere and telomere specific DNA libraries has improved the resolution of detecting all classes of radiation induced chromosomal inter- and intra-changes. Newly obtained data indicate that (a) FISH-based translocation assay is a unique model to assess acute as well as chronic exposure in cases of accidental as well as occupational exposure to ionizing radiation, either immediately following exposure, or retrospectively. This assay is capable of defining accumulative effects to red bone marrows. (c) Studies on the spectra of radiation induced chromosome aberrations revealed two distinct hallmarks for high LET radiation in comparison to low LET radiation. (d) Premature chromosome condensation assay proved to be a unique method to be used for immediate dose assessment at low (5cGy) as well as high doses (≥3 Gy) and to discriminate between whole- and partial-body exposure in case of mass casualties and accidental over-exposure to high doses of ionizing radiation. Furthermore, this assay is combined with multi-colour FISH assay, and for the first time could reveal the nature of chromosomal instability in primary tumours at different stages.

The outcomes of these studies lead to improve international radiation protection standards for protracted exposures, which is the most frequent form of occupational and population exposure in society.