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THERA-NOSTICS Targeted Theraputic LU177- PSMA -617 DIAGNOSTIC COMPANION GA68-PSMA 11 - Pet/CT PSMA -Many prostate cancer cells have a protein on the surface called PS MA (prostate specific membrane antigen). PSMA 6I7 Ligand is a small peptide (molecule ) with a high binding affinity for PSMA. When injected into the bloodstream it looks for the PSMA exuded on the surface of the prostate cancer cells and bonds to it. This ligand not only bonds to PSMA – it also bonds to Lutetium 177 and Gallium 68 (Ga 68). Gallium 68 is a radioactive isotope. From the time it is made radioactive in the hospital laboratory, it only has a half life of 68 minutes. Lutetium177 is also a radioactive isotope which when made radioactive has a half life of 6.64 days. To determine if you are suitable for Lutetium treatment Firstly a Gallium 68 scan is done Gallium 68 is mixed with the PSMA 11 Ligand, this blend is then injected into the bloodstream. The mixture circulating through the bloodstream is attracted to the protein and starts to build up on the surface of the cancer cel ls (in much the same way as iron filings are attracted to a magnet). If there is no PSMA on the cancer cells – you are NOT considered to be PSMA Avid - the Ligand /Gallium 68 blend will just keep circulating and without any PSMA to adhere to, it will be passed in your urine. When the scan is done – there will be nothing to see – so if you are given a dose of Lutetium 177 / ligand blend it too will do nothing, i t will just pass through the bladder and be excreted with your urine. As the Lutetium177/ Ligand blend will have no PSMA to build up on, you will NOT be considered suitable for treatment with Lutetium177. If you are PSMA avid The Ligand /Gallium 68 blend wi ll keep circulating and be attracted to the protein on the surface of the cancer cells and continue to build up on the surface. This will show up on the scan so the location of the PSMA avid cancer cells can be seen. In this case you maybe suitable for treatment with Lutetium177 but suitability still depends on the results of an FDG scan. Secondly a F18 FDG (Glucose ) scan is done If there is no PSMA on the surface of the cancer cells, the Ga68 scan will show nothing but there could still be cancer present – cancer which is not showing up. This is why it is important to have a F18 FDG (Glucose ) scan. This scan can show cancer which does not exude PSMA and in this case, treatments other than Lutetium 177 would have to be considered. When the two scans do not show prostate cancer in the same position, the scans are considered to be discordant - in which case you are not considered to be a suitable candidate for treatment with Lutetium177 - it just won’t work. When you receive a Lutetium177 injection — it starts circulating through the bloodstream, building up on the protein on the surface of the prostate cancer cells and starts killing the cells beneath the protein. The radiation from this (Lu-PSMA) beta mixture only penetrates about 1mm ,so it will not damage the surrounding non-cancerous tissue. It keeps working flat out for approx 7 and a bit days, and then slowly ceases working over the next few weeks as the radioactivity of the Lutetium177 decays Further Ga68 Scans will show the results of the Lutetium177 treatment.