Complex and simple chromosomal exchanges induced by sparsely and densely ionizing radiation in vitro and in vivo

It is well-known that sparsely and densely ionizing radiations have a different relative biological effectiveness (RBE) for the induction of chromosomal aberrations. In addition, the different local dose distribution results in a different aberration spectrum. The most promising biomarker for densely ionizing radiation is the ratio C of complex (three or more breaks) to simple (two breaks) chromosomal exchanges [1]. The C-ratio induced in peripheral blood lymphocytes in vitro and in vivo by X-rays and C-ions was determined using the mFISH method. The cells were obtained from a healthy volunteer and irradiated in vitro or from prostate cancer patients undergoing radiotherapy with C-ion boost and IMRT (see [2] for details). Figure 1 shows the number of simple and complex exchanges induced in lymphocytes by in vitro exposure to X-rays and C-ions with different energies. Based on these results the C-ratio was calculated. For X-ray irradiation, the C-ratio shows a clear dose-dependent increase from 0.06 ± 0.04 at 1 Gy to 0.54 ± 0.07 at 4 Gy. High-energy C-ions show values similar to X-rays, while spread-out Bragg peak (SOBP) C-ions induced a significantly higher C-ratio (0.71 ± 0.14 after 1 Gy and 0.62 ± 0.08 after 2 Gy).