Comparison of [18F] fluorocholine (FCH) uptake and perfusion in 9L glioma tumor model

Objectives The oncologic radiotracer, FCH, exhibits rapid blood clearance, suggesting uptake in tissues may be highly dependent on perfusion. In this study, intratumoral FCH uptake and perfusion were studied.

Methods 9L glioma cells were implanted subcutaneously in Fisher rats (n=4) and tumors grown to ~20 mm diameter. Regional FCH deposition and tumor perfusion were compared at submillimeter spatial resolution by 2-D autoradiography of ¹⁸F/¹⁴C following administration of FCH and the perfusion marker, [¹⁴C]iodoantipyrine (IAP). Tumors were excised, frozen and sliced at 5 min and 20 min after IV bolus administration of FCH. Intravenous infusion of IAP began 1 min prior to termination of experiment. Quantitative maps of regional perfusion were obtained.

Results Both perfusion and FCH uptake were seen primarily at the periphery of the tumor with FCH distribution showing slightly greater penetration into the tumor. At 5 min, FWHM of FCH distributions at the periphery was 7.6 ± 1.6 mm, where as FWHM of perfusion was 3.1 ± 2.2 mm. Peak perfusion in the tumor periphery ranged from 0.11-0.17 ml/g/min. There was a 50% reduction in peak FCH retention from 5 min to 20 min post-injection, however the intratumoral distributions remained equivalent.

Conclusions FCH uptake pattern followed closely the intratumoral distribution of perfusion. Washout of FCH from 5 min to 20 min may reflect clearance of non-phosphorylated tracer in presence of hypoxia. The study suggests that the heterogeneity of tumor uptake of choline analogs depends largely on the heterogeneity of perfusion and should be carefully considered in interpreting the results in implanted tumor models.