26. Chromosomal damage and survival of keratinocytes and fibroblasts after irradiation with 200 kV or 25 kV X-rays

Abstract

A relative biological effectiveness of 1 is accepted for soft X-rays (25–30 kV), which are applied in diagnostic radiology (mammography). However, it has been shown that soft X-rays can be more effective in cell killing and chromosomal damage. The present study was initiated to define biological effects of low-energy X-rays in vitro. Experiments were performed with 25 kV X-rays and 200 kV reference X-rays on neonatal human keratinocytes (HEKn), and NIH/3T3 mouse fibroblasts. Cell survival was studied with graded doses in a clonogenic assay, chromosomal damage in a micronucleus (MN) assay. The surviving fraction at 2 Gy for keratinocytes was 46±5% after 200 kV and 33±11% after 25 kV X-rays. Linear-quadratic cell survival analysis yielded α=0.305±0.033 Gy-1 and β=0.048±0.011 Gy-2 for 200 kV and α=0.399±0.103 Gy-1 and β=0.048±0.054 Gy-2 for 25 kV. For 3T3 fibroblasts an SF2 of 53±3% after 200 kV and 61±18% after 25 kV was observed. Values of α=0.24±0.02 Gy-1 and β=0.022±0.002 Gy-2 for 200 kV and α=0.10±0.05 Gy-1 and β=0.070±0.010 Gy-2 for 25 kV were derived. In conclusion, keratinocyte survival was similar for both radiation qualities. For fibroblasts, a reduction in survival at higher doses was observed. Results from MN studies will be presented.