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Purpose: Cells receiving ionising radiation influence the survival of non-irradiated neighbouring cells through cellular communication (Bystander effects). The aim of this study is to identify conditions for bystander expressions at different doses and times after exposure to ionising radiation of therapeutic energies, using a medium transfer technique. Methods: Donor flasks plated with non-small lung cancer cells, NCI-H460, were exposed to 0 (control), 1, 4, 8 Gy using a 6 MV photon beam. Donor flasks were incubated for designated time periods, then the irradiated conditioned culture medium (ICM) was transferred to non-irradiated receiver cells. Receiver cells were incubated for 5-7 days to form colonies, which were then counted. The data were reported in the form of survival fraction (SF). Results: Proliferative bystander effects, corresponding to bystander effect Type II, were observed at 1 Gy and 8 Gy. At 8 Gy and 1 hour following irradiation a 21% increase in survival fraction was observed. At 4 Gy the ICM has a cytotoxic effect on the receiver cells, corresponding to bystander effect Type I, exhibiting a maximum response at 15 minutes after irradiation. Conclusion: Two types of bystander expression were established in a single cell line. The results provide in vitro evidence to suggest that when lethal doses of radiation are administered to a tumour volume, peripheral non-irradiated regions that contain subclinical disease may show a proliferative response. |
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