BACKGROUND: In clinical radiotherapy most patients tolerate the applied dosage 
with no or moderate side effects. However, 5 to 10% of all individuals show 
increased acute and/or late reactions. In-vitro test systems are investigated 
for their suitability for predictive purposes. This paper attempts a correlation 
between the induction and repair of DNA damage measured in the comet assay and 
the clinical observed reaction in order to evaluate the suitability of the comet 
assay for prediction of radiation sensitivity.
PATIENTS AND METHODS: Skin fibroblasts of 30 patients with average tissue 
reactions or acute and/or late increased side effects and cell lines of 4 
individuals carrying the heritable disease ataxia telangiectasia (AT) were 
irradiated in vitro. The induction and repair of DNA damage was measured at 
different time points after irradiation in the comet assay (single cell gel 
electrophoresis). These results were compared to the acute and late clinical 
reactions classified according to the RTOG grading system.
RESULTS: The radiation induced DNA damage decreased over time reflecting DNA 
repair. Cells of the AT individuals showed an elevated damage induction and a 
reduced repair capacity compared to patients with average tissue reactions. 
Fibroblasts of patients with increased acute and late side effects exhibited 
slower DNA repair. In addition to the known lack of cell cycle control, our 
results indicate that AT cells show reduced DNA repair capacity.
CONCLUSIONS: The comet assay seems to be able to detect some types of increased 
individual radiation sensitivity. In contrast to other predictive in-vitro 
tests, the comet assay needs less time and fewer cells, which would be useful in 
a clinical setting.