Radiotoxicity of 11C-methionine measured by the accumulation of DNA strand breaks in mammalian cells.

The radiotoxic effects of L-[methyl-11C] methionine were estimated by measuring the accumulation of DNA strand breaks. CHO, Chinese-hamster cells, were incubated in 11C-methionine-containing medium for 60 min at 37 degrees C. The number of unrepaired DNA strand breaks was then examined by the DNA-unwinding method. For comparison, cells were also externally irradiated under similar conditions with gamma radiation (137Cs) or positrons (11C). The relative biological effectiveness of 11C-methionine was estimated to be about 1.