Imaging with positron emission tomography (PET) in prostate cancer represents an important clinical advance, especially for identifying metastases. Its use has expanded significantly, especially outside of the United States. In this interview, Mark Frydenberg, MD, discusses the evolution of PET scanning, its clinical indications, its advantages and drawbacks, and key questions that remain about its use. Dr. Frydenberg is professor of surgery, Monash University, and academic director of urology, Cabrini Institute, Cabrini Health, Melbourne, Victoria, Australia. Dr. Frydenberg was interviewed by Urology Times Editorial Consultant J. Brantley Thrasher, MD, executive secretary of the American Board of Urology, Charlottesville, VA.
To start, tell me what you consider positron emission tomography (PET) scanning today and how it has evolved.
PET scanning today has moved on from where it was previously with vastly improved tracers. We’re really looking for an imaging tool that better identifies metastatic spread of any malignancy, in this case, prostate cancer. Urologists have been well aware of PET scans in the past and had used PET choline scans, but they never became popular because they weren’t particularly sensitive and specific. Choline is also quite difficult and expensive to produce; it requires a cyclotron on site.
Since then, other PET tracers have been studied, including sodium fluoride, which is very good at detecting bone metastases. More recently, people have looked at fluciclovine F18 (Axumin), and in Australia where I practice, the most common one is a Gallium 68 PET PSMA scan, which is prostate-specific membrane antigen.
The dissemination of PET scanning now in Australia is well ahead of the United States. How is it being used in Australia?
Its use has really exploded in Australia over the last 5 years or so. The reason is that most of the nuclear medicine departments actually have their own gallium generators. As such, it is relatively quick, easy, and inexpensive to manufacture and deliver, so the dissemination has been very rapid in both public and private sectors.
The main use for PET initially was in biochemical recurrence following definitive treatment for prostate cancer, predominantly radical prostatectomy, but also primary radiotherapy. It’s also been used to monitor metastatic disease, especially in the setting of castrate-resistant disease, and more recently it’s been used in primary staging, in particular in patients with high-risk prostate cancer, to look for oligometastatic spread.
There’s worry always in the U.S. about cost. What would be a similar cost for a PET scan in U.S. dollars, and how are you able to justify the cost in certain patient groups?
The cost in Australia would be approximately $500 U.S., so it has become quite affordable. It is not something that the government pays for the patient right now. Government approvals for payment of new technologies often take 2 to 3 years so it may be some time before it is covered for the general public by a government rebate. However, it is readily available in virtually all of the university public hospitals in Australia. Many of the private providers also have access to PET PSMA, with most patients being reasonably comfortable paying for it privately if it’s not covered through the university hospital.
It obviously is important to use it wisely because there is a direct patient cost associated with it, especially in the U.S. As such, it’s important to try to choose the patients who are most likely to have a positive scan. In the primary staging setting, there’s no doubt we really need to look at the high-risk cases only. For the intermediate- and low-risk cases, less than 5% of patients will have a positive PET scan, and it will probably not be a cost-effective strategy for them. However, most of the studies looking at high-risk prostate cancer have shown 30% to 50% of patients do show oligometastatic sites on a PET PSMA scan, so it’s definitely worthwhile to consider it in that population.
The other group where it should be considered is obviously those with biochemical recurrence, and we’ve learned there is probably little point in doing a PET PSMA scan when PSA is below 0.2 ng/mL. The likelihood of a positive result is very low in that group, but it starts increasing from 0.2 ng/mL onwards. Most of the data show that about 30% of patients with PSA between 0.2 and 0.5 ng/mL will have a positive PET PSMA scan. That will increase to about 60% when PSA is between 0.5 and 1.0 ng/mL and will increase to about 80% when it’s above 1.0 ng/mL.