Biokinetics and dosimetry for [methyl-11C]thymidine

The uptake and retention of [methyl-11C]thymidine in organs and tissues after intravenous injection were studied using positron emission tomography scanning of patients. In addition, clearance of 11C-activity from the blood was determined directly by measurements of blood-samples. 5 min after administration the activity level was already reduced to 5% of the initial activity after injection. Preferential uptake of 11C-activity was present in the liver and kidneys. A less pronounced uptake was observed in the skeletal muscle tissue, heart wall, lungs and salivary glands. The retention in these organs and tissues has a long half-life compared with the physical half-life of 11C. The absorbed dose per unit activity administered was calculated for all critical organs following the Medical Internal Radiation Dose Committee formalism. Averaging over the patients, values of 37 and 28 microGy MBq-1 were obtained for the liver and the kidneys respectively. The committed effective dose after a [methyl-11C]thymidine scan with 740 MBq, a commonly applied amount of activity for this type of scan, is 2.8 mSv.