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PET scanning and prostate cancer management today

Posted Dec 24 2009 12:00am

The role of positron emission tomography or PET scanning in the work-up and management of prostate cancer patients is evolving. However, the average patient needs to understand that, outside a major research center, where researchers have access to a wide range of different “tracers” (the agents used to help to highlight cancer cells), when it comes to prostate cancer, PET scanning is not usually able to do some of the things we most need it to do it a very reliable manner.

Most PET scans are carried out using a tracer known as 18F-fluoro-2-deoxy-2-D-glucose (18F-FDG). The problem is that this tracer is not good at highlighting prostate cancer — to identify either primary prostate cancer lesions or prostate cancer that has metastasized to the bones. Because of this, also, Medicare does not yet reimburse for the use of PET scanning as a diagnostic procedure in the treatment of prostate cancer (even though Medicare did significantly expand coverage of PET scanning for cancer diagnosis in April 2009).

Now this does not mean that PET scanning has no value in the management of prostate cancer. What it does mean, however, is that patients should be extremely cautious about getting PET scans for suspected prostate cancer outside a well constructed clinical trial. And if the PET scan is part of a clinical trial, then you shouldn’t have to pay for it!

The “New” Prostate Cancer InfoLink suggests that there are some key questions you need to ask before going for a PET scan:

  • Is this scan part of a clinical trial to evaluate the use of PET scans in the diagnosius and work-up of prostate cancer patients?
  • Will the costs of this scan be covered by my insurance provider if it is not being done as part of a clinical trial?
  • What tracer is being used?
  • What exactly is your physician hoping to be able to see on the PET scan?

PET scans are more likely to produce useful results for prostate cancer patients when they are combined with CT scans. Combination PET/CT scans allow the radiologist to superimpose the PET scan results onto the CT scan, which means that (s)he can make a much more accurate estimation of the precise location of any signal for the presence of prostate cancer indicated by the PET scan, particularly if a choline or acetate tracer is being used rather than 18F-FDG. But even choline and acetate tracers are not as good at imaging prostate cancer as what we really need.

The recent article by Hong et al., referred to above, describes work on a wide spectrum of new imaging agents that may be better suited to the identification of prostate cancer (inside and outside the prostate) than either choline or acetate (see also Rohren and Macapinlac). The advent of such new agents may well allow us to use PET or PET/CT scans with much greater accuracy as a method to diagnose and stage patients with prostate cancer — particularly those with high- and intermediate-risk disease – but we have a way to go before this can be achieved with a high and reliable degree of accuracy.


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