Biological Effects of Ionising Radiation-with Special Emphasis on Low Level Doses

Abstract

Cancer induction is assumed to be dominating for radiation risk in the low dose range (<100 mSv). Generally it cannot be determined by epidemiology after such low doses for a normal population. The risk is extrapolated from medium and high dose ranges therefore. For prospective radiological protection a linear dose response without a threshold (LNT) is proposed although this has not been definitely proven until now. It is therefore assumed that biological studies can contribute in order to solve the question whether health effects are caused by small radiation doses. In this respect many studies have been focussed on DNA damage, chromosomal aberrations, and more recently on epigenwetic (non-targeted) effects, gene expression and proteomics.

It is necessary to evaluate the mechanisms which lead to radiation-induced health effects. Biological phenomena are modulating these effects. Such phenomena are adaptive response, apoptosis, bystander effects, DNA repair, genetic disposition, genomic instability and immunological phenomena. Many data have been published with respect to these effects after radiation during recent years. However, it is usually unknown with which steps these processes interfere in the development of health effects. Further quite often the dose response of these biological effects is also unclear in the low dose range.

It has to be recognized that the radiation effects are dependent on the age of the exposed person, on sex and on genetic disposition. With respect to exposures of patients the pathological features of the disease may also have relevant implications on radiosensitivity. Under such conditions and uncertainties for the evaluation of radiation risk in the low dose range it is not justified to calculate risk values like deaths after doses in the range of several mSv for a general population of patients. However, this can be done in individual cases.