Investigation on different qualities of radiation regarding their genotoxic effects

The relative biological effectiveness (RBE) of protons with two different LETs (linear energy transfer) of 1.64 and 2.84 keV/μm and of thermal neutrons was investigated compared to γ-Co60-rays as standard source using the cytokinesis block micronucleus assay. A possible relationship between the genotoxic effect and the physical parameter 'high temperature ratio' (HTR) was investigated. Therefore fibroblast cultures and lymphocytes were irradiated in a dose range of about 0.2 Gy and 2.0 Gy and their micronuclei (MN) were countered. The investigation of the genotoxic effect of protons showed significant intraindividual variabilities (p < 0.01 to 0.05), while no interindividual variability was detectable. With both, protons and Co60, a linearquadratic dose-response was obtained. Proton irradiation with LET of 1.64 keV/μm showed a weaker dose-response curve compared to LET of 2.84 keV/μm. The RBE and the HTR depended on the LET and the dose. The values decreased with the increasing dose. The higher LET led to higher RBE and HTR values. The RBE and the HTR correlated excellently (r = 0.99). In this study the biological effectiveness of proton irradiation could be shown and assessed only by the physical investigation of the parameter HTR. (author)