What is a prostate scan?
Prostate cancer is the third leading type of cancer behind lung cancer and breast cancer. It commonly spreads to bone but can spread to lymph nodes and other body structures.
Prostate Specific Membrane Antigen (PSMA) is a protein molecule expressed on the surface of prostate cells and more so on prostate cancer cells. Anti-PSMA antibodies have been discovered that bind to these PSMA antigens that makes the immune system aware that these antigens are being expressed in greater numbers although the immune response appears to be limited.
What nuclear pharmacists have done is to chemically bind these antibodies to a radioactive substance that emits specialized rays called gamma rays. This radiation and its gamma rays, while given in extremely low dose (much lower radiation than conventional x-rays), can be detected by the specialized detectors on a machine called a gamma camera or PET-CT camera.
The benefit of this is that the chemical compound injected is available to the whole body and as such allows us to survey the body for multiple areas of increased PSMA expression
e.g. in cancer spread to bone and soft tissues.
This gives your doctor an indication of how advanced the cancer or infective process is, thereby assisting him or her in their decision making with regards to future treatment plans.
What can be expected to happen?
You will be asked to drink plenty of water to allow for urinary clearance of any excess tracer that isn’t bound to bone. Furthermore, you will
be required to empty you bladder prior to imaging so that the pelvic bones can be well visualized.
This may need to be repeated.
If the gamma camera technique is used initial imaging will be at one hour after the radiopharmaceutical injection. This is in the form of a whole body 2-dimensional image that has the greatest sensitivity for picking up potential lesions although it does not give much information as to lesion location.
A second scan is performed at three hours after radiopharmaceutical injection – a whole body 3D SPECT-CT scan. While not being as sensitive as the whole body 2D images, provides excellent localization of lesion. The two studies combined gives the best overall performance.
Where PET-CT technique is performed instead, the scan is performed in one sitting 1 hour after tracer injection. The decision of technique depends on availability of the type of radiation attached to the anti-PSMA antibody.
Where lesions are demonstrated they will appear
“hotter” than other areas.
The nuclear physician (specialist doctor) will then look at all these images and come to a conclusion about your condition that will be of benefit to your doctor and ultimately for you.
