Measurement of biological effects of high-energy carbon ions at low doses using a semi-automated cell detection system.

PURPOSE

To study the effects of low-dose, high-LET irradiation in order to detect possible deviations from a linear-quadratic dose dependence.

MATERIALS AND METHODS

Experiments using charged particle irradiation were performed, in particular in the low-dose range from 0 to 2 Gy, and compared with experiments using photon radiation. The survival of V79 cells was studied by means of a semi-automated system, which allowed the detection and relocation of positions of individual cells at regular intervals. It consists of an inverted microscope equipped with a computerized stage control and image processing system. With such a technique, the precision of the survival assay is increased by avoiding the stochastic uncertainties of the conventional dilution assay. Furthermore, by means of daily observations, the system allows a detailed study of the growth kinetics of individual cells up to approximately 1 week after irradiation.

RESULTS AND CONCLUSION

Up to now, high-LET experiments have been performed using mainly 100 MeV/u carbon ions (LET: 28 keV/microm). A significant hypersensitivity at low doses (0.1 Gy) has been detected for these ions. It is the first report of such a pronounced effect for charged particle irradiation. Although hypersensitivity after carbon ion irradiation apparently is in contrast to other data reported for peak pion irradiation at similar LET values, the difference might possibly be due to differences in the track structure of the particles.