Analysis of Prostate Cancer Imaging Agents: F-18 Fluciclovine vs. F-18 PSMA

Introduction: One of the biggest challenges of all diagnostic imaging methods is to accurately detect the recurrence of prostate cancer (PCa). There are two PET/CT agents used for this analysis -- F-18 fluciclovine (Axumin) and F-18 PSMA. In December 2020, F-18 PSMA became FDA approved in the U.S. which made it available for use by hospitals across the country. This has caused a sudden influx of orders for PSMA within providing institutions throughout the last few months. Up until now, Axumin has been the primary agent used for prostate cancer imaging. The objectives of this study are to: identify differences in image quality between Axumin and PSMA, summarize the advantages and disadvantages of using these two PET agents, analyze Gleason score and PSA statistics to find correlations in metastatic volume, conduct a comparative analysis among patients who underwent both scans, and recommend the most effective radiopharmaceutical for pre/post-therapy recurrent disease localization.

Methods: A literature review was conducted to gather information on both PSMA and Axumin as it pertains to their chemical structure, pathophysiology, image quality, and lesion detection potential. Advantages and disadvantages to using each of these agents were compared. PSMA and Axumin studies were then quantitatively analyzed with a patient sample composed of 20 Axumin studies and 20 PSMA studies. These patients were selected based upon their availability of Gleason scores, PSA levels, and corresponding scans. After scans were acquired, respective metastatic volumes and affected organ systems were analyzed. This data was used to see if correlations could be found between rising PSA levels, Gleason scores, and metastatic volume for either agent. A comparative analysis was done between the two agents to determine which would be better for the future of localizing and imaging prostate cancer based upon their data correlations and image quality.

Results: Overall, PSMA was able to detect a greater number of lesions than Axumin in patients that had undergone both scans. However, PSMA also showed intense uptake in the bladder due to urinary clearance; this issue was not present in Axumin studies. No correlation has been found between rising Gleason scores and metastatic volumes for either agent. A correlation between PSA levels and metastatic volume was found in the PSMA images. This correlation was less consistent in the Axumin images, so results are inconclusive. Through the comparative analysis done of PSMA and Axumin scans performed at this institution, it was found that patients who have had undergone both scans recorded a higher metastatic volume in the PSMA scans than the Axumin scans.

Conclusions: The correlations between Gleason scores, PSA levels, and metastatic volume of PSMA and Axumin were analyzed in this study. No correlation was found between the Gleason scores and metastatic volume for either agent; this is attributed to the fact that the Gleason score can increase as cancer progresses, but it cannot regress. So, if a patient is treated and their cancer begins to regress, their Gleason score will still be high. A correlation between PSA levels was found; as PSA levels increased, so did lesion detection and metastatic volume on PET/CT images. This correlation was more prevalent with PSMA than it was with Axumin. These findings correlated well in the comparative study of patients who underwent both scans. In theory, there should have been similar metastatic volumes in both the Axumin and PSMA scan. This was not the case as a higher volume of metastases was found in the PSMA scan around the pelvic girdle which were not able to be visualized in the Axumin scan. This study highlights the significance of using PSMA imaging agents for PET/CT imaging of prostate cancer. Institutions should understand the implications of using Axumin and consider implementing PSMA imaging for prostate cancer, where available.