Rapid and sensitive response of carbon-11-L-methionine tumor uptake to irradiation

Evaluation of cancer treatments by the measurement of tumor size is an unsatisfactory method for the observation of the radiobiologic response of the tumor. After 20 Gy single-dose irradiation of 60Co to rat tumor AH109A, the L-[methyl-11C] methionine tumor uptake, the microscopic extension of tumor necrosis and the shrinkage of tumor were compared quantitatively. L-[Methyl-11C]methionine uptake fell to 54 +/- 19% of non irradiated tumor at 12 hr after irradiation. Necrosis extended 49 +/- 7% of total tissue volume after 3 days. Tumor volume decreased 48 +/- 12% 10 days after irradiation. L-[Methyl-11C]methionine uptake by tumor showed a sharp and rapid linear decrease after irradiation and the response of the uptake to irradiation preceded the extension of necrosis and tumor shrinkage. We conclude that radiation effect on the tumor may be evaluated immediately after irradiation by the measurement of L-[methyl-11C]methionine uptake and thus clinical application of positron emission tomography may give a benefit to the patients undergoing radiotherapy.