Pilot study: PET imaging might improve prostate cancer diagnosis and treatment

A pilot study suggests a near real-time method of imaging prostate cancer to aid in organ-sparing treatments, and an innovative as well as accurate way to see whether the cancer has spread.

Science figure with PET/MRI images
18F-DCFPyL imaging of a 64-year-old male with primary PCa (Gleason score 5+4=9, cT2c, PSA 8.4 ng/mL). Maximal intensity projection 18F-DCFPyL PET image at 120 min p.i. (a) shows two foci of prostate cancer (arrows) with a dominant focus at the right mid peripheral zone of the prostate gland and a smaller focus at the contralateral site. The T2 weighted MRI (b), and PET/MRI fusion images (c) confirm the accuracy of 18F-DCFPyL in targeting prostate cancer at 120 min p.i.

These dual findings stem from research reported in Molecular Imaging and Biology on a relatively new radiotracer used in dynamic positron emission tomography (PET) to detect levels of prostate-specific membrane antigen (PSMA), an indicator of prostate cancer. 

The radiotracer (18F-DCFPyL) was recently approved by the Food and Drug Administration (FDA) for staging men with prostate cancer as candidates for initial definitive therapy. It was also approved for patients with suspected recurrent prostate cancer based on elevated levels of prostate-specific antigen (PSA). The FDA guidelines state to inject the radiotracer and wait one hour before imaging. This is based on an earlier study that informed the approval process.

But the research team led by Stephen Adler of the Frederick National Laboratory wanted to take a closer look at uptake of the radiotracer over time. In a small clinical study, they evaluated the radiotracer’s pharmacokinetics and performance at early time points and after a two-hour delay. The two-hour delay would allow more time for the radiotracer to attach to cancer cells.

“The second focus was on the fact that it does uptake quickly, and how do we take advantage of that,” Adler said.

The study enrolled 10 volunteers ages 61 to 81 with confirmed high-risk prostate cancer. Each was injected with the radiotracer and imaged with dynamic PET imaging over 45 minutes and a static PET snapshot at two hours after injection. Tumor uptake values were assessed after five minutes, 30 minutes, and two hours. The radiotracer was taken up at increasingly higher concentrations with the optimal images obtained after two hours, but a clear identification of tumors after just five minutes.

These results indicate that two hours is the optimal wait time for evaluating localized prostate cancer, although not necessarily ideal for use in routine clinical practice, the scientists reported. And since the tumors can be seen as early as five minutes, PET imaging with 18F-DCFPyL could provide immediate feedback during organ-sparing treatments such as focal laser ablation, high-intensity focused ultrasound, and radiofrequency ablation.

The integration of PSMA-based PET imaging into the routine evaluation of prostate cancer has markedly improved the accurate disease staging, including identification of metastatic disease, and has improved treatment decisions.   

It is reasonable to suppose that PSMA PET may soon be a part of the routine diagnostic flowchart in many prostate cancer patients for planning primary therapy and possibly before targeted tumor biopsy,” said Esther Mena, a member of the research team

Adler noted that this is a small pilot study, and additional in-depth research is needed for a more definitive analysis and to confirm early time points for the effective use of PET imaging to monitor therapeutic interventions in real time.