11C-Acetate PET/CT Non-FDG-Avid Tumors

Recent publications have suggested the use of 11C-acetate as another PET tracer for tumor imaging. The accumulation of 11C-acetate in tumor cells is related to the highly active lipid metabolism in the cell membrane associated with tumor growth. 11C-acetate is channeled into the tricarboxylic acid cycle via acetyl coenzyme A and then incorporated via phosphatidylcholine into the cell membrane's phopholipids. Possible biochemical paths of acetate incorporation or accumulation include (a) entering the Krebs cycle from acetyl coenzyme A (acetyl CoA) or as an intermediate metabolite, (b) esterification to form acetyl CoA as a major precursor in ß-oxidation for fatty acid synthesis, (c) combining with glycine in heme synthesis, and (d) through citrate for cholesterol synthesis. Of all of these possible metabolic pathways, participation in free fatty acid (lipid) synthesis is believed to be the dominant method of incorporation in tumors. The clinical data on the role of 11C-acetate PET in human tumors is being accumulated. Most clinical studies have investigated the role of 11C-acetate PET in detection of prostate cancer. 11C-acetate PET was found valuable in the detection of recurrent prostate cancer, both in the prostate bed, lymph nodes and distant metastases. The main advantage of 11C-acetate is that it does not show physiological accumulation in the urinary bladder as is the case with 18F -FDG and therefore may be appropriate for the detection of active pelvic disease. Comparing the uptake of 18F-FDG and of 11C-acetate in patients with lung carcinoma, the latter was found superior in the identification of a bronchiolo-alveolar carcinoma which often show no intense FDG uptake. In the case of hepatic masses, well-differentiated HCC tumors were detect by 11C-acetate while poorly differentiated types were detected by 18F-FDG. These data suggest that 11C-acetate PET may be valuable in the detection of well-differentiation slow growing tumors and may have a complementary role to the routinely used 18F-FDG.