C11-Choline PET in

Urinary System Tumors

[C-11]Choline is a new radiopharmaceutical that we have pioneered for the application of  PET in urinary system tumors.

Methyl Choline labeled with 11C (11C-MC) is a promising new agent for tumor imaging using PET. Evidence suggests increased synthesis of membrane phosphatidylcholine in tumor cells that is correlated with high uptake of this radiopharmaceutical into malignant tissue. In contrast to 18F -fluorodeoxyglucose (FDG), its uptake into benign structures such as the normal brain, heart and urinary tract is negligible, resulting in a higher target to background signal ratio in tumors located near those benign structures.

Another advantage is its rapid disappearance from the blood-pool, within minutes, while the plateau of  18F –FDG uptake into tumors may be reached only after hours. Therefore, diagnostic content of 11C-MC images is already stable after 5-15 minutes. Our aim is to evaluate the usefulness of PET imaging with 11C-MC for the diagnosis, staging and therapeutic follow-up of malignant tumors. An automated synthetic route to 11C-MC was developed in our lab including QC procedure.  [11C] carbon dioxide is produced in the cyclotron and subsequently iodinated to form  [11C] methyl iodide. [Methyl-11C] choline is synthesized by the reaction of [11C] methyl iodide with "neat" dimethylaminoethanol at 120 degrees C for 5 min. 

Purification is achieved by evaporation of the reactants followed by passage of the aqueous solution of the product through a cation-exchange resin cartridge. Radiochemical yield is > 98%. Radiochemical purity is > 98%. Chemical purity is > 90% (dimethylaminoethanol is the only possible impurity). Specific radioactivity of the product is > 133 GBq/mumol. The final product is tested for pyrogens by the limulus lysate test. The recommended dose is around 370 Mbq. A quality assurance method based on cation-exchange HPLC was developed. Human study of [11C]Choline-PET was approved by the Helsinki Committee and more than 50 cases of either brain, prostatic and urinary system tumors have been studied up to now.