Effect of gamma-radiation on the ratio of [F-18]2-fluoro-2-deoxy-D-glucoseto glucose utilization in human glioblastoma cells in vitro

The glucose consumption in tumours in vivo as reflected by uptake of [F-18] 2-fluoro-2-deoxy-D-glucose ((18)FDG) using positron emission tomography (PE T) is currently under investigation as a measure of tumour response to radi otherapy. The calculation of cerebral metabolic rate of glucose from (18)FD G-PET data requires a proportionality factor referred to as the lumped cons tant. In the present in vitro study, the utilizations of (18)FDG and glucos e have been measured in a human glioblastoma cell line (86HG-39) as a funct ion of gamma-radiation dose with various post-irradiation times and of diff erent fractionation modes. The ratio of utilization of (18)FDG to that of g lucose (R-F/G), assumed to correspond to the lumped constant, was observed to increase 12 and 24 h after single fraction gamma-exposure by factors ran ging from 1.2 to 1.5 compared with the non-irradiated controls. It decrease d after multiple fraction gamma-exposure (4 x 2 Gy) by a factor of 0.7 comp ared with the single fraction schedule (1 x 8 Gy). The results suggest that the affinities of glucose transporters or hexokinase enzyme pr both for (1 8)FDG and glucose could be influenced by gamma-irradiation in this tumour c ell line in vitro. Apparent changes of the glucose consumption determined w ith PET in human tumours following radiotherapy may, therefore, not be sole ly due to changes in cellular metabolism or cell number but may also be due to changes in R-F/G.