Following his review of available imaging modalities, Brian Helfand, MD, PhD, considers which scans are most appropriate based on patient and disease factors.
Brian Helfand, MD, PhD: How do we know which patients are the most suitable for each imaging modality? As I mentioned, there are many PET [positron-emission tomography]–CT scans available. Using choline, fluciclovine, PSMA [prostate-specific membrane antigen]—various PSMAs are FDA approved and on the market, and even more are coming—how do you know which is the right type of PET-CT to obtain? That’s a big question and a moving target in the field.
Unfortunately, there are almost no head-to-head studies. Most studies that have been conducted have had patients on 1 arm or another arm or haven’t had scans that have been temporarily close in time. That makes interpretation of the data quite challenging. We don’t know what the true winner is. There has been some suggestion—and not an overwhelming consensus—that PSMA scans may be more sensitive at very low PSA [prostate-specific antigen] levels, less than 0.5 ng/mL. But if you look at the literature, there’s some debate.
If you have access to every type of scan that you want to, and you have a patient with a low PSA, you may want to start with a PSMA. But if you don’t have access to PSMA and you have only fluciclovine, it’s not inappropriate to start with that scan because there are data supporting that even at those low levels, you’re going to find positive metastatic deposits, and you’ll be able to make your plan based on that. That’s ill-defined, and as PSMA scans come on the market, we still don’t know which 1 is the best for each scenario. In the situation here—a 66-year old man who received some hormone therapy but now is off hormone therapy—we don’t understand which is better, especially if it’s a localized recurrence, then maybe it’s at the urethral anastomosis. The example I gave was in pelvic lymph nodes. But if it was in localized, in the prostate bed or the urethral anastomosis, we don’t know which PSMA modality is the best.
The 2 [PSMA scans] on the market are a gallium-based PSMA and a 18F-DCFPyL scan. The difference is that the gallium-based scan is excreted in the urine, so that could obscure any local recurrence or any recurrence in the bladder or urethral anastomosis. The 18F-DCFPyL may not have the same obscuring because it’s not excreted as much in the urine. These are subtleties, but we still don’t know, No. 1, if that influences our detection rate and, No. 2, if that’s going to change our management based on what you use. Therefore, I subscribe to the fact that if you have access to a PSMA PET-CT scan or a fluciclovine-based scan, use what you have available. If you have multiple scans, look at the PSA level. If it’s low, consider a PSMA scan out of the gate.
Transcript edited for clarity.