PREDICTION OF RADIOTHERAPEUTIC EFFECTS ON TUMOR USING POSITRON EMISSION TOMOGRAPHY

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To evaluate tumor imaging potential of 18F-fluoromisonidazole (FMISO), we studied FMISO uptake in an experimental tumor model and examined the correlation between intra-tumoral distributions of FMISO, 14C-2-deoxyglucose (2DG) and 14C-methionine (Met). Methods: We studied the issue distribution and double tracer autoradiography using control rats with AH109A tumor and rats with the same tumor under local hypoxia. Results: Tumor uptake of FMISO was constant between 30 min to 2 hr after injection, and the tumor to muscle ratio was 2, from 2 to 4 hr. A tumor study with FMISO was scheduled at 2 hr. Double tracer autoradiography of the tumor demonstrated that in the areas of high FMISO uptake, there was low uptake of Met, while low FMISO uptake areas showed high Met uptake. FMISO showed high grain density in the rim of the tumor surrounding the necrotic area. 2DG showed more uniform distribution over the entire section of viable cells. The mean uptake of FMISO by hypoxic, radioresistant tumors was significantly higher than the control tumors (p<0.05), while both 2DG and Met uptake by the control tumor were higher than hypoxic tumor. When individual tumors were examined, the uptake of FMISO was inversely correlated with that of Met (r=-0.507, p<0.02), while 2DG showed almost uniform uptake with no significant correlation to FMISO. Conclusions: Hypoxic and radioresistant tumour can be identified by increased FMISO uptake in our model consistent with works reported by others. We found a large overlap in the distribution of FMISO and 2DG within the tumor, but only a small overlap in the distribution of FMISO and Met. A combination of FMISO and other tracers in PET or SPECT study would possibly be more helpful than single tracer study in predicting the response of tumor tissues to radiotherapy.