11C]methionine quantitation in cancer PET studies.

Quantitation of the uptake of positron emitting tracers in cancer patients is still unsettled. A uniform method is needed for comparison of results and for collecting a data base of tumor PET studies. We have measured the tumoral uptake of [11C]methionine in 46 cancer patients using four different methods of analysis. The accumulation of [11C]methionine at 35-40 min after the injection adjusted to the injected dose and body surface area turned out to give similar results as a more complicated method where the uptake rate of [11C]methionine from the plasma to the tumor was calculated (r = 0.92, p less than 0.0001). The results suggest that in clinical [11C]methionine PET studies, 40 min emission scanning with frequent blood sampling is unnecessary. Only a single 5 min emission scan 25-40 min after the injection is required for analysis if the accumulation is adjusted to the injected dose and body surface area.