Assessment of cancer recurrence in residual tumors after fractionated radiotherapy: a comparison of fluorodeoxyglucose, L-methionine and thymidine.
This study evaluates the midterm follow-up of tumor and normal tissue uptake of deoxyglucose, thymidine and methionine after fractionated radiotherapy to assess cancer recurrence in residual tumors.


METHODS
AH109A tumor-burdened rats were treated with one to eight doses of 5Gy 60Co radiation. Tissue distribution study with 18F-FDG, 3H-thymidine and 14C-methionine, double-tracer autoradiography with 18F-FDG and 14C-methionine, and single-tracer autoradiography with 14C-labeled deoxyglucose, thymidine and methionine were performed 6 days after the end of therapy.


RESULTS
Dose response study shows a significant decrease of tumor uptake of all tracers after two and more doses, even in the case of later recurrence. Whereas 3H-Thd and 14C-Met tumor uptake was similar to that of normal muscle, 18F-FDG tumor uptake remains higher than that of muscle, even in the case of complete tumor cure. The irradiated muscle shows a higher 18F-FDG uptake than the nonirradiated muscle. Autoradiography after eight doses (100% tumor cure) reveals elevated 14C-DG tumor uptake to be ascribable to nonmalignant cellular elements, in particular to a macrophage layer at the rim of necrotic areas. Autoradiography after four and six doses (33% and 57% tumor cure) shows the highest methionine and thymidine uptake in viable cancer cells, whereas deoxyglucose uptake did not differ between viable cancer cells and macrophages.


CONCLUSIONS
To detect and differentiate viable cancer cells in a residual tumor mass after radiotherapy, PET using 11C-methionine or 11C-thymidine may have some advantages over 18F-FDG, especially if the residual tumor includes larger areas of necrosis.
Reinhardt
M J
MJ
Department of Nuclear Medicine and Radiology, Tohoku University, Sendai, Japan.
Kubota
K
K
Yamada
S
S
Iwata
R
R
Yaegashi
H
H
D000818:Animals; D001345:Autoradiography; D002250:Carbon Radioisotopes / Q000493:pharmacokinetics; D003847:Deoxyglucose / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D004307:Dose-Response Relationship, Radiation; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics; D019788:Fluorodeoxyglucose F18; D008297:Male; D008715:Methionine / Q000493:pharmacokinetics; D018365:Neoplasm, Residual / Q000000981:diagnostic imaging* / Q000473:pathology; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D051381:Rats; D013936:Thymidine / Q000493:pharmacokinetics; D014055:Tomography, Emission-Computed; D014316:Tritium / Q000493:pharmacokinetics
D002250:Carbon Radioisotopes; D005462:Fluorine Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D014316:Tritium; D003847:Deoxyglucose; D008715:Methionine; D013936:Thymidine