Inactivation of C3H 10T½ Cells by Monoenergetic High LET Alpha-particles

Abstract

Inactivation of mouse C3H 10t½ cells in plateau-phase (7·8 × 10⁴ cells/cm²) was studied by using α-particles from the irradiation facility installed for radiobiological experiments at the 3 MV Tandem accelerator, University of Naples. Silicon detectors and CR39 plastic track detectors were employed for dosimetric purposes. The cells were exposed to high LET monoenergetic α-particles (energy of 1·8 MeV at the centre of the cell nucleus, track-averaged LET of 177 keV/µm and dose-rate of 1·1 Gy/min) and low-LET 80 kVp X-rays. The X-ray survival curve showed a significant shoulder (α/β = 9 Gy) while the survival curve for α-particles was close to exponential. The mean lethal dose of α-particles was 0·77 ± 0·02 Gy and the RBE was 5·2 at 80% survival and 3·0 at 5% survival. Survival of exponentially growing cells (2 × 10⁴ cells/cm²) following irradiation with the α-particle beam is also reported. The nuclear areas of 10T½ cells were measured as 299 ± 9 µm² and 250 ± 8 µm² for cells in log phase and plateau phase, respectively. The inactivation cross-section, obtained from the mean lethal dose, was 34 µm² and 37 µm² for cells in log phase and plateau phase, respectively. These values appear to be the maximum measured values for the inactivation cross-section of 10T½ cells as a function of the α-particle LET. This saturation cross-section is very similar to the saturation values reported in the literature for other mammalian cell lines.