Fiducial Marker Seeds for Prostate Cancer: What They Do and Why They're Used
Dear Dr. Greenstein,
I was diagnosed with localized prostate cancer and I have chosen to have radiation therapy. My radiation oncologist wants my urologist to place marker seeds in my prostate before the treatment start. Why?
External beam radiation is excellent choice for men to treat localized prostate cancer. As technologies advance, radiation oncologists are able to treat prostate cancer with better accuracy. In the past, the radiation oncologist would treat the entire prostate area. This included the bottom of the bladder, the rectum and the urethra. Some patients had side effects such as overactive bladder or diarrhea. Today, the radiation delivered to treat to prostate cancer is becoming so precise that we are seeing less side effects.
However, the prostate is an organ that moves everyday and moves as a patient breathes. If the prostate moves a 1/4 inch one day, the radiation delivered can injure the rectum, bladder or other surrounding structures. For the last few years, urologists have been placing gold fiducial markers in the prostate gland to help the radiation oncologist see the prostate gland when the patient has his daily treatment. Some patients my require a testosterone blocking hormone injection to slow the progression of their prostate cancer. This medication is started a few weeks before the markers are inserted.
Gold fiducial markers are tiny gold markers that are 2.0 to 3.0 mm in size. That's about 0.11 inch in size. The markers are inserted using the same method a prostate biopsy is performed. A transrectal ultrasound is performed in the urologist's office. The prostate is measured. Depending on the patient, the prostate can be anesthetized with 1.0 % lidocaine. In general, three gold fiducial markers are then inserted through a needle which is passed through the ultrasound probe. The ultrasound provides the urologist with the ability to precisely place the markers in strategic positions.
There are a few rare side effects with inserting the markers. This includes infection, temporary local pain and blood in the urine, stool and semen.
The markers are used as a fixed standard of reference for comparison or measurement every time the patient has their radiation treatment. The radiation oncologist uses X-ray to locate the markers when a patient gets their treatment. This allows the radiation to be delivered to the prostate with precision and accuracy. This greatly diminishes injury to the surrounding organs. The combination of improving radiation technology and use of gold fiducial markers has the abilityto expand the use external beam radiation therapy for men with prostate cancer.