The prostate-specific membrane antigen (PSMA) is an excellent target for theranostic applications in prostate cancer (PCa). However, PSMA-targeted radioligand therapy can cause undesirable effects due to high accumulation of PSMA radiotracers in salivary glands and kidneys. This study assessed orally administered monosodium glutamate (MSG) as a potential means of reducing kidney and salivary gland radiation exposure using a PSMA targeting radiotracer. Methods: This prospective, double-blind, placebo-controlled study enrolled 10 biochemically recurrent PCa patients. Each subject served as his own control. [ 18 F]DCFPyl PET/CT imaging sessions were performed 3-7 days apart, following oral administration of either 12.7 g of MSG or placebo. Data from the two sets of images were analyzed by placing regions of interest on lacrimal, parotid and submandibular glands, left ventricle, liver, spleen, kidneys, bowel, urinary bladder, gluteus muscle and malignant lesions. The results from MSG and placebo scans were compared by paired analysis of the ROI data. Results: A total of 142 pathological lesions along with normal tissues were analyzed. As hypothesized a priori, there was a significant decrease in maximal standardized uptake values corrected for lean body mass (SULmax) on images obtained following MSG administration in the parotids (24 ± 14%, P=0.001), submandibular glands (35 ± 11%, P<0.001) and kidneys (23 ± 26%, P=0.014). Significant decreases were also observed in lacrimal glands (49 ± 13%, P<0.001), liver (15 ± 6%, P<0.001), spleen (28 ± 13%, P=0.001) and bowel (44 ± 13%, P<0.001). Mildly lower blood pool SULmean was observed after MSG administration (decrease of 11 ± 13%, P=0.021). However, significantly lower radiotracer uptake in terms of SULmean, SULpeak, and SULmax was observed in malignant lesions on scans performed after MSG administration compared to the placebo studies (SULmax median decrease 33%, range-1 to 75%, P<0.001). No significant adverse events occurred and vital signs were stable following placebo or MSG administration. Conclusion: Orally administered MSG significantly decreased salivary gland, kidney and other normal organ PSMA radiotracer uptake in human subjects, using [ 18 F]DCFPyL as an exemplar. However, MSG caused a corresponding reduction in tumor uptake, which may limit the benefits of this approach for diagnostic and therapeutic applications.

Purpose To investigate the relationship of 24- and 48-hour metformin discontinuation to bowel uptake of fluorine 18 fluorodeoxyglucose (FDG) on PET/CT scans. Materials and Methods Patients with diabetes who were treated with metformin and referred for FDG PET/CT were randomized to three equal groups based on duration of metformin discontinuation: 24 hours, 48 hours, and no discontinuation (control group). Two interpreters blinded to the study groups assessed FDG uptake in multiple segments of small and large bowel qualitatively and semiquantitatively by using maximum standardized uptake values (SUVs). Differences in age, sex, weight, dose of metformin, duration of metformin treatment, blood glucose levels, and FDG dose injected were assessed. Data were analyzed with analysis of variance when passing normality, and by nonparametric testing when not. Results Ninety study participants (62 male, 28 female; median age, 70 years) were enrolled from July 2010 through March 2012. There were no differences between study groups in weight, blood glucose levels 3 days prior to scanning, or normal organ uptake. Large bowel SUV was lower after 24 hours (4.10 ± 2.00 vs 5.42 ± 2.36; P = .020) and 48 hours (2.63 ± 0.88 vs 5.42 ± 2.36; P ˂ .001) of metformin discontinuation than for no discontinuation (control), and for 48 hours versus 24 hours of discontinuation (P = .0015). Small bowel SUV was lower after 24 hours (2.86 ± 0.67 vs 3.73 ± 1.08 [control]; P ˂ .001) and 48 hours (2.78 ± 0.73 vs 3.73 ± 1.08 [control]; P ˂ .001) of metformin discontinuation versus no metformin discontinuation, but not for 48 hours versus 24 hours of discontinuation (P = .57). Examination-day blood glucose levels increased after 48-hour withdrawal of metformin (8.41 mmol/L ± 2.86 vs 6.83 mmol/L ± 2.13 [control]; P = .002). Conclusion Metformin discontinuation for 48 hours prior to PET/CT was associated with lower accumulation of fluorodeoxyglucose in the bowel, compared to when there was no discontinuation (control group) or 24-hour discontinuation of metformin. © RSNA, 2018.

on behalf of the EANM Technologist Committee; Elizabeth A. Bailey 5 on behalf of the ANZSNM Technologists Special Interest Group; Norman E. Bolus 6 on behalf of the SNMMI Technologist Section; and Tina M. Alden 7 on behalf of CAMRT