The effect of microcolony size, at time of irradiation, on colony forming ability

Purpose: To investigate the effect of irradiating microcolonies of various sizes on their subsequent ability to form colonies. Materials and methods: The location of individual HPV-G cells in tissue cul ture flasks was recorded using computerized microscopy. This allowed the ce lls' positions to be continually revisited, which enabled manual sizing of individual microcolonies both at the time of irradiation (between 0-5 Gy) a nd following an incubation period during which the microcolonies were asses sed for cologenic survival. Results: The experiments indicate that when irradiated as microcolonies, ce lls have plating efficiencies (PE) that are lower than expected when compar ed with the prediction fr om the PE values of cells irradiated individually . Conclusion: These data support the conclusions of Mothersill and Seymour (1 997b) which challenge the concept of independent survival of certain types of cells following irradiation. The results indicate that interactions betw een cells can occur even in small aggregates.