ESTIMATION OF INTERNAL ABSORBED DOSE OF L-[METHYL-C-11]METHIONINE USING WHOLE-BODY POSITRON-EMISSION-TOMOGRAPHY

L-[Methyl-C-11]-methionine (C-11-methionine) is proposed as a useful r adiotracer for tumour diagnosis. Human biodistribution data of cumulat ed activities and absorbed doses estimated by the MIRD (medical intern al radiation dosimetry) method for C-11-methionine are not available i n the literature. In this study we measured the organ activity for C-1 1-methionine by using whole-body positron emission tomography (PET) an d estimated the absorbed doses to 25 organs by the MIRD method. Whole- body dynamic PET scans were per formed on five normal volunteers to me asure the time course of the organ activity concentration (activity/vo lume) after intravenous administration of C-11-methionine. Cumulated a ctivities of the ten source organs were calculated fi om the time-acti vity curves, obtained from the dynamic PET data, Absorbed dose estimat es were performed by the MIRD method for the Caucasian reference man a nd for the Japanese reference man. The organs which received the highe st absorbed doses for the Caucasian reference man were found to be the bladder wall (2,7x10(-2) mGy/MBq), the pancreas (1.9x10(-2) mGy/ MBq) , the liver (1.8x 10(-2) mGy/MBq) and the kidney (1.1x10(-2) mGy/MBq). The effective doses for the Caucasian reference man and the Japanese reference man were calculated as 5.2x10(-3) and 5.0x10(-3) mSv/MBq, re spectively.