Radiobiological characterization of human tumor cell multilayers after conventional and particle irradiation.

The goal of this study was to establish planar multilayers from human tumor cells (WiDr and SiHa) as a model for irradiation of solid tumors. In addition to using conventional X rays (250 kV) as a reference standard, multilayers were tested for their suitability in cell survival studies with heavy-ion irradiation ((12)C(6+)) in the plateau and the extended Bragg peak with a scanned ion beam. Multilayers of both cell lines showed decreased survival compared to the corresponding monolayers after both X and heavy-ion irradiation. This multicellular sensitization effect is in contrast to the multicellular resistance or contact effect commonly described in the literature. Flow cytometry measurements showed an arrest of irradiated SiHa cells in G(2)/M phase. In contrast to the transient arrest of the monolayers, the multilayers stayed in a prolonged arrest. After Bragg-peak irradiation of monolayers, the arrest time was increased by 12-24 h, and more cells were arrested than with X rays. For multilayers, there were no differences between G(2) arrest after X rays and heavy ions for the entire observation period.