Early differences in dynamic uptake of 68Ga-PSMA-11 in primary prostate cancer: A test-retest study

Abstract

Introduction Dynamic PET/CT allows visualization of pharmacokinetics over the time, in contrast to static whole body PET/CT. The objective of this study was to assess 68Ga-PSMA-11 uptake in pathological lesions and benign tissue, within 30 minutes after injection in primary prostate cancer (PCa) patients in test-retest setting. Materials and methods Five patients, with biopsy proven PCa, were scanned dynamically in list mode for 30 minutes on a digital PET/CT-scanner directly after an intravenous bolus injection of 100 MBq 68Ga-PSMA-11. Approximately 45 minutes after injection a static whole body scan was acquired, followed by a one bed position scan of the pelvic region. The scans were repeated approximately four weeks later, without any intervention in between. Semi-quantitative assessment was performed using regions-of-interest in the prostate tumor, bladder, gluteal muscle and iliac artery. Time-activity curves were extracted from the counts in these regions and the intra-patient variability between both scans was assessed. Results The uptake of the iliac artery and gluteal muscle reached a plateau after 5 and 3 minutes, respectively. The population fell apart in two groups with respect to tumor uptake: in some patients the tumor uptake reached a plateau after 5 minutes, whereas in other patients the uptake kept increasing, which correlated with larger tumor volumes on PET/CT scan. Median intra-patient variation between both scans was 12.2% for artery, 9.7% for tumor, 32.7% for the bladder and 14.1% for the gluteal muscle. Conclusion Dynamic 68Ga-PSMA-11 PET/CT scans, with a time interval of four weeks, are reproducible with a 10% variation in uptake in the primary prostate tumor. An uptake plateau was reached for the iliac artery and gluteal muscle within 5 minutes post-injection. A larger tumor volume seems to be related to continued tumor uptake. This information might be relevant for both response monitoring and PSMA-based radionuclide therapies.

Is there more than meets the eye in PSMA imaging in prostate cancer with PET/MRI? Looking closer at uptake time, correlation with PSA and Gleason score

“…As previously mentioned, while the potential of early dynamic PSMA PET has already been thoroughly explored in the context of 68 Ga-PSMA-11 (Uprimny et al 2017a ; Schmuck et al 2017 ; Olde Heuvel 2021 ; Sachpekidis et al 2018 ; Barakat et al 2020 ) and even investigated for 18 F-PSMA-1007 in one study (Sachpekidis et al 2019 ), to the best of the authors’ knowledge, late PSMA kinetics has not been a topic of any research so far, regardless of the type of the PSMA tracer. Given the lack of literature in this domain, we were curious about all the possible information we could extract as the added value of this PET acquisition already present and approved in the clinical routine.…”

“…While the early dynamic uptake of PSMA has already been a focus of a few study groups (Uprimny et al 2017a ; Schmuck et al 2017 ; Olde Heuvel 2021 ; Sachpekidis et al 2018 ; Barakat et al 2020 ), the late dynamics have not yet been assessed, to the best of the authors’ knowledge. The PSMA uptake at later time points has been evaluated only in the form of static scans (Schmuck et al 2017 ), therefore not investigating the signal kinetics at that later stage, its potential added value for understanding the PSMA accumulation and clearance in different lesions, or even potential correlations of those behaviours with other available clinical parameters.…”

The effect of eating on the uptake of PSMA ligands in the salivary glands

“…Since in our study the stimulation was immediate, an increase in blood flow would result in more unbound PSMA being delivered to the salivary glands than when compared to a stimulation at 1 h post injection, where most of the PSMA is already bound. PSMA-ligand concentration in arteries decays by 80% and plateaus within 5 min of tracer administration [29]. Furthermore, given that our study showed only a small effect size, it is unsurprising they found no significant differences.…”

Effects of furosemide and tracer selection on urinary activity and peri-bladder artefacts in PSMA PET/CT: a single-centre retrospective study

“…Significantly higher urinary bladder activities were found in 18 F-DCFPyL compared to 68 Ga-PSMA-11 for the respective subgroups with and without furosemide. Theoretically the difference in timepoint of acquisition between the 18 F-DCFPyL cohorts and the 68 Ga-PSMA-11 cohorts (60 and 45 min PI, respectively) could, by continuing urinary excretion of tracer in that timeframe, contribute to higher urinary activity in the 18 F-DCFPyL cohorts [ 13 ]. However, the observed differences in biodistribution time did not lead to a significant effect in the multivariate analysis, leaving choice of tracer and furosemide as independent factors influencing urinary bladder activity.…”