Early effects of irradiation on [(123)I]-IMT and [(18)F]-FDG uptake in rat C6 glioma cells.

BACKGROUND

Single-photon emission computed tomography (SPECT) using 3-[(123)I]-iodo-L-alpha-methyltyrosine ([(123)I]-IMT) and positron emission tomography (PET) using 2-[(18)F]-fluoro-2-deoxy-D-glucose ([(18)F]-FDG) are valuable tools for the distinction between viable tumor and radionecrosis in patients receiving radiotherapy for high-grade gliomas. However, to date, little is known about the early effects of radiation on [(123)I]-IMT and [(18)F]-FDG uptake in gliomas.

MATERIAL AND METHODS

To determine the early effects of irradiation on [(123)I]-IMT and [(18)F]-FDG uptake in gliomas, in vitro studies were performed using rat C6 glioma cells. The glioma cells were irradiated with 20 Gy which is a common dose applied to patients receiving intraoperative radiotherapy. Subsequently, the early kinetics of [(123)I]-IMT and [(18)F]-FDG uptake in glioma cells were monitored for 3 days.

RESULTS

Micromorphometric examinations of the irradiated glioma cells revealed that about 25% of the viable cells transformed into giant cells. [(123)I]-IMT uptake per 10(5) viable glioma cells was unchanged on the 1st day post irradiation, but showed a significant increase on the 2nd and 3rd day following radiotherapy (p < 0.01). In addition, there was a moderate increase in [(18)F]- FDG accumulation per 10(5) viable glioma cells during the first 3 days after irradiation (p < 0.05). The maximum increase in early [(123)I]-IMT uptake 1 h after application surpassed that of [(18)F]-FDG (p < 0.01).

CONCLUSION

Rat C6 glioma cells show an early increase in [(123)I]-IMT and [(18)F]-FDG uptake following irradiation which may be partly due to giant cell formation. These data suggest that [(123)I]-IMT SPECT and [(18)F]-FDG PET may be promising procedures for the early prediction of the therapeutic response of gliomas to radiotherapy.