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  1. Paul Edwards (not a doctor) says: For some time I’ve been wanting to gather together all the bits and pieces in the forum on PET Scans. Whatever you do have a look at the amazing video at the end of this post. A positron emission tomography (PET) scan is an imaging test that uses a radioactive substance called a radiotracer to look for disease in the body. Before carrying out a PET scan, a radioactive medicine is produced in a cyclotron (a type of machine). The radioactive medicine is then tagged to a natural chemical. This natural chemical could be glucose, water, or ammonia. The tagged natural chemical is known as a radiotracer. The radiotracer is then inserted into the patient’s body, normally through a canula which has been inserted into the patient’s arm. When it is inside, the radiotracer will go to areas inside the body that use the natural chemical. For example, the 18F-FDG (fluorodeoxyglucose) is a radiotracer that is tagged to glucose. The glucose goes into those parts of the body that use glucose for energy. Cancers, for example, use glucose differently from normal tissue - so, an FDG PET Scan can show up cancers. The 18F-FDG PET Scan is probably the commonly used PET Scan in hospitals. Because prostate cancer is slow-growing, it does not take up glucose as much as other cancers. For this reason researchers have been looking to develop radiotracers that were more suitable to use for imaging prostate cancer. For several years the 11C-Choline PET scan introduced at the Mayo Clinic has been regarded as leading the way in the imaging of prostate cancer. The major limitation of 11C-Choline is that it has a 20-minute half-life (The half life is the time required for one half of the atoms of a given amount of a radioactive substance to disintegrate). This means that 11C-Choline must be used very quickly after it is produced. For this reason, it must be produced on site very close to where it is administered. Normally radiotracers are produced off site for safety reasons. 11C-Choline has shown limited sensitivity in men with very low PSAs. One study showed a 5% detection rate where PSA levels were less than 1. 18F-Fluorocholine is another radiotracer that has been trialled in Europe and Australia with good results. However, it is less sensitive than 11C-Choline and requires a higher PSA level in order to get an effective image. A PSMA PET scan is one that uses a radiotracer which is targeted to a protein (Prostate-Specific Membrane Antigen) that is found in prostate cancer. There are different types of radiotracers are being developed for PSMA PET Scans. For example, in the United States Johns Hopkins University has developed a 18F-DCFBC radiotracer and Memorial Sloan Kettering Cancer Centre has developed a Zr89-J591 radiotracer. In Australia we are now using a Gallium(Ga68) radiotracer which was developed in Germany. The Gallium PSMA PET Scan produces a sharply defined image at very low PSA levels. Because the Gallium PSMA PET Scan targets the Prostate-Specific Membrane Antigen protruding from the outer membrane of the cancer cells, the radiotracer “lights up” on the PET images showing clearly metastases to lymph nodes as well as to bone. [in my case with a very low PSA of 0.58, the Gallium PSMA PET Scan detected 4 metastases that were not visible on other scans.] Seeing is believing. Memorial Sloan Kettering Cancer Centre has produced an excellent video showing the difference that a PSMA PET Scan makes: http://www.mskcc.org/videos/prostate-specific-pet-scans Whilst radiology oncologists are predicting that the PSMA PET Scan will revolutionise the treatment of prostate cancer, that revolution is some time away. At the moment the technology is still being trialled in Australia. There is limited availability of these scans: only a few hospitals in Australia are offering them. The scans are expensive and are not covered by Medicare.
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