CAN COLONY SIZE BE USED TO DETECT LOW-DOSE EFFECTS

Many insults at low doses are defined as nontoxic, even though obvious effects do occur. Among these are changes in colony size when clonoge nic survival is assessed. Early attempts to quantify radiation effects on colony size have been reported, but the time-consuming nature of t hese experiments did not encourage the use of this parameter as an end point. Recently, however, developments in image cytometry technology have provided alternative, less labor-intensive means of measuring col ony size. These techniques have been used in our ongoing investigation s of radiation effects at low doses. Data accumulated to date show a m easurable dose dependence of colony size in clones classed as survivor s. This dose dependence is characterized by fluctuations in the 0-1.5- Gy dose range, followed by a gradual decrease in colony size at higher doses. The fluctuations at low doses correspond qualitatively to the concavity, thought to be indicative of inducible repair phenomena, tha t has been observed in cell survival curves in the same dose range. Th is concavity was also seen in the current study, but its detection app eared to be dependent on the method used to score survivors.