Abstract
1030
Objectives 11C-CNS5161 (N-(2-chloro-5-methylthiophenyl)-N′-(3-methylthiophenyl)-N′-[11C]methylguanidine) has been successfully used in positron emission tomography (PET) imaging of N-methyl-D-aspartate (NMDA) receptors. However, no human dosimetry data has been published. We are planning to use this radiotracer for investigating NMDA receptor function in three categories of subjects: (i) systemic lupus erythematosus; (ii) traumatic brain injury; and (iii) Parkinson’s disease. We have, therefore, undertaken PET imaging using 11C-CNS5161 to measure whole body distribution of this radionuclide and estimate radiation dose to various organs.
Methods Dynamic PET studies of the whole body were performed in five normal adult subjects. Regions-of-interest were drawn over the visualized structures. Resultant time-activity curves were generated and used to determine residence times for dosimetry calculations. S-factors were computed using the OLINDA/EXM software for each structure/organ.
Results For 11C-CNS5161, organ doses ranged from 0.0006 to 0.1455 rads/mCi. The critical organ for radiation burden was the lungs with a dose of 0.1455 rads/mCi. Radiation dose to the reproductive and blood forming organs were 0.0086, 0.0006 and 0.0074 rads/mCi for ovaries, testes, and red marrow, respectively. The effective dose equivalent (EDE) was 0.0392 rems/mCi.
Conclusions The radiation dosimetry for 11C-CNS5161 for a standard single injection of 15 mCi will result in an EDE of 0.59 rems and lung dose of 2.18 rads in young normal subjects.
Research Support This research was supported by the National Institutes of Health, Grant No. 1P01AI073693-05 and the Lupus Foundation of America, Grant No. 113121.