TY - JOUR T1 - Characterizing and Mitigating Bladder Radioactivity on <sup>18</sup>F-fluciclovine PET/CT JF - Journal of Nuclear Medicine Technology JO - J. Nucl. Med. Technol. DO - 10.2967/jnmt.119.230581 SP - jnmt.119.230581 AU - Petra Lovrec AU - David M. Schuster AU - Robert Wagner AU - Medhat Gabriel AU - Bital Savir-Baruch Y1 - 2019/10/01 UR - http://tech.snmjournals.org/content/early/2019/10/10/jnmt.119.230581.abstract N2 - Purpose: F-18-fluciclovine PET is approved for prostate cancer recurrence imaging. According to the radiopharmaceutical package insert only 3% of the tracer is expected to be excreted in the urine over the first four hours. Yet, in clinical practice we noticed a higher percentage of bladder excretion. We sought to evaluate and quantify early fluciclovine bladder radioactivity and determine if refraining from voiding before fluciclovine injection would mitigate it. Materials and Methods: 159 patients underwent fluciclovine PET/CT imaging as part of their clinical workup. The first 36 patients were instructed to void just before fluciclovine injection, the subsequent 123 patients were not requested to void. The SUVmax and SUVmean of the bladder, aorta, marrow, liver, and bladder volumes were collected. Comparing SUVmean of bladder to background, we characterized bladder radioactivity as: "Insignificant" (bladder &lt; aorta), "Mild" (bladder &gt; aorta, &lt; marrow), "Moderate" (bladder &gt; marrow, &lt; liver) and "Intense" (bladder &gt; liver). Differences between the protocols were investigated. Results: Overall, 22% (35/159) of patients had moderate, and 8.8% (14/159) had intense bladder activity. A negative association was found between bladder volumes and SUVmean. A significant difference was found between voiding and non-voiding protocol groups, with 38.9% (14/36) vs. 17.1% (21/123) of patients having moderate, and 22.2% (8/36) vs. 4.9% (6/123) of patients having intense bladder activity, respectively. Conclusion: Refraining from voiding prior to F-18-fluciclovine injection results in significantly lower urinary bladder radioactivity compared to purposeful voiding pre-injection. We have modified our practice accordingly, particularly as moderate and intense bladder activity may mask/mimic local prostate cancer recurrence. Mechanisms underlying this phenomenon should be further investigated. ER -