Feasibility of fluorine-18-fluorophenylalanine for tumor imaging compared with carbon-11-L-methionine.
L-[methyl-11C]methionine (11C-Met) is a useful tracer for tumor imaging with PET. The drawbacks include a short half-life and high physiological accumulation in abdominal organs. To overcome these shortfalls, the feasible use of [18F]fluorophenylalanine (18F-Phe), which shares the same amino acid transport system with Met, for tumor imaging was examined.


METHODS
The time course of tissue distribution of 18F-Phe and the tumor uptake response to radiotherapy were compared with 14C-Met and [3H] thymidine (3H-Thd) in the rat AH109A tumor model. Intratumoral distribution of 18F-Phe was compared with 14C-Met and 14C-Thd using double-tracer macroautoradiography (ARG). We also evaluated whole-body ARG.


RESULTS
Tumor uptake of 18F-Phe peaked at 60 min postinjection and was higher than that of the liver, intestine and kidney but lower than the pancreas. Tumor uptake of 18F-Phe was similar to that of 14C-Met. Tumor-to-blood and tumor-to-muscle ratios were higher in 14C-Met compared with that of 18F-Phe because of the rapid blood clearance of 14C-Met. With whole-body ARG, the tumor was clearly visualized with high contrast. Radiotherapeutic response of tumor uptake of 18F-Phe was as rapid as that with 14C-Met and with 3H-Thd. Intratumoral distribution of 18F-Phe and 14C-Met were identical, and 18F-Phe and 14C-Thd were similar.


CONCLUSIONS
Fluorine-18-Phe seems to be a potentially useful amino acid tracer for tumor imaging with a longer half-life than 11C, with higher tumor contrast in the abdomen than Met and a similar sensitive response to radiotherapy.
Kubota
K
K
Department of Nuclear Medicine and Radiology, Tohoku University, Sendai, Japan.
Ishiwata
K
K
Kubota
R
R
Yamada
S
S
Takahashi
J
J
Abe
Y
Y
Fukuda
H
H
Ido
T
T
D000818:Animals; D001345:Autoradiography; D002250:Carbon Radioisotopes / Q000493:pharmacokinetics; D005240:Feasibility Studies; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics; D006207:Half-Life; D008114:Liver Neoplasms, Experimental / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D008297:Male; D008715:Methionine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D011877:Radionuclide Imaging; D051381:Rats; D011919:Rats, Inbred Strains; D013936:Thymidine; D013997:Time Factors; D014018:Tissue Distribution; D014316:Tritium
D002250:Carbon Radioisotopes; D005462:Fluorine Radioisotopes; D014316:Tritium; C027217:2-fluorophenylalanine; D010649:Phenylalanine; D008715:Methionine; C038344:methionine methyl ester; D013936:Thymidine