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

Direct Patlak Reconstruction of [68Ga]Ga-PSMA PET for the Evaluation of Primary Prostate Cancer Prior Total Prostatectomy: Results of a Pilot Study

To investigate the use of kinetic parameters derived from direct Patlak reconstructions of [68Ga]Ga-PSMA-11 positron emission tomography/computed tomography (PET/CT) to predict the histological grade of malignancy of the primary tumor of patients with prostate cancer (PCa). Thirteen patients (mean age 66 ± 10 years) with a primary, therapy-naïve PCa (median PSA 9.3 [range: 6.3-130 µg/L]) prior radical prostatectomy, were recruited in this exploratory prospective study. A dynamic whole-body [68Ga]Ga-PSMA-11 PET/CT scan was performed for all patients. Measured quantification parameters included Patlak slope (Ki: absolute rate of tracer consumption) and Patlak intercept (Vb: degree of tracer perfusion in the tumor). Additionally, the mean and maximum standardized uptake values (SUVmean and SUVmax) of the tumor were determined from a static PET 60 min post tracer injection. In every patient, initial PSA (iPSA) values that were also the PSA level at the time of the examination and final histology results with Gleason score (GS) grading were correlated with the quantitative readouts. Collectively, 20 individual malignant prostate lesions were ascertained and histologically graded for GS with ISUP classification. Six lesions were classified as ISUP 5, two as ISUP 4, eight as ISUP 3, and four as ISUP 2. In both static and dynamic PET/CT imaging, the prostate lesions could be visually distinguished from the background. The average values of the SUVmean, slope, and intercept of the background were 2.4 (±0.4), 0.015 1/min (±0.006), and 52% (±12), respectively. These were significantly lower than the corresponding parameters extracted from the prostate lesions (all p < 0.01). No significant differences were found between these values and the various GS and ISUP (all p > 0.05). Spearman correlation coefficient analysis demonstrated a strong correlation between static and dynamic PET/CT parameters (all r ≥ 0.70, p < 0.01). Both GS and ISUP grading revealed only weak correlations with the mean and maximum SUV and tumor-to-background ratio derived from static images and dynamic Patlak slope. The iPSA demonstrated no significant correlation with GS and ISUP grading or with dynamic and static PET parameter values. In this cohort of mainly high-risk PCa, no significant correlation between [68Ga]Ga-PSMA-11 perfusion and consumption and the aggressiveness of the primary tumor was observed. This suggests that the association between SUV values and GS may be more distinctive when distinguishing clinically relevant from clinically non-relevant PCa.

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

BACKGROUND

In patients with increasing PSA and suspicion for prostate cancer, but previous negative biopsies, PET/MRI is used to test for tumours and target potential following biopsy. We aimed to determine different PSMA PET timing effects on signal kinetics and test its correlation with the patients' PSA and Gleason scores (GS).

METHODS

A total of 100 patients were examined for 900 s using PET/MRI approximately 1-2 h p.i. depending on the tracer used (⁶⁸Ga-PSMA-11, ¹⁸F-PSMA-1007 or ¹⁸F-rhPSMA7). The scans were reconstructed in static and dynamic mode (6 equal frames capturing "late" PSMA dynamics). TACs were computed for detected lesions as well as linear regression plots against time for static (SUV) and dynamic (SUV, SUL, and percent injected dose per gram) parameters. All computed trends were tested for correlation with PSA and GS.

RESULTS

Static and dynamic scans allowed unchanged lesion detection despite the difference in statistics. For all tracers, the lesions in the pelvic lymph nodes and bones had a mostly negative activity concentration trend (78% and 68%, resp.), while a mostly positive, stronger trend was found for the lesions in the prostate and prostatic fossa following RPE (84% and 83%, resp.). In case of ⁶⁸Ga-PSMA-11, a strong negative (R_min = - 0.62, R_max = - 0.73) correlation was found between the dynamic parameters and the PSA. ¹⁸F-PSMA-1007 dynamic data showed no correlation with PSA, while for ¹⁸F-rhPSMA7 dynamic data, it was consistently low positive (R_min = 0.29, R_max = 0.33). All tracers showed only moderate correlation against GS (R_min = 0.41, R_max = 0.48). The static parameters showed weak correlation with PSA (R_min = 0.24, R_max = 0.36) and no correlation with GS.

CONCLUSION

"Late" dynamic PSMA data provided additional insight into the PSMA kinetics. While a stable moderate correlation was found between the PSMA kinetics in pelvic lesions and GS, a significantly variable correlation with the PSA values was shown depending on the radiotracer used, the highest being consistently for ⁶⁸Ga-PSMA-11. We reason that with such late dynamics, the PSMA kinetics are relatively stable and imaging could even take place at earlier time points as is now in the clinical routine.

A Systematic Review of the Variability in Performing and Reporting Intraprostatic Prostate-specific Membrane Antigen Positron Emission Tomography in Primary Staging Studies

Context

Prostate cancer (PCa) remains one of the leading causes of cancer-related deaths in men worldwide. Men at risk are typically offered multiparametric magnetic resonance imaging and, if suspicious, a targeted biopsy. However, false-negative rates of magnetic resonance imaging are consistently 18%; therefore, there is growing interest in improving the diagnostic performance of imaging through novel technologies. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) is being utilised for PCa staging and, more recently, for intraprostatic tumour localisation. However, significant variability has been observed in how PSMA PET is performed and reported.

Objective

In this review, we aim to evaluate how pervasive this variability is in trials investigating the performance of PSMA PET in primary PCa workup.

Evidence acquisition

Following the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines, we performed an optimal search in five different databases. After removing duplicates, 65 studies were included in our review.

Evidence synthesis

Studies dated back as early as 2016, with numerous different source countries. There was variation in the reference standard for PSMA PET, with some using biopsy specimens or surgical specimens, and in some cases, a combination of the two. Similar inconsistencies were noted when studies selected histological definitions of clinically significant PCa, while some omitted their definition altogether. The most significant variations in performing PSMA PET were the radiotracer type, dose, acquisition time after injection, and the PET camera being utilised. Substantial variation in the reporting of PSMA PET was noted, with no consistency in defining what constitutes a positive intraprostatic lesion. Across 65 studies, four different definitions were used.

Conclusions

This systematic review has highlighted considerable variation in obtaining and performing a PSMA PET study in the context of primary PCa diagnosis. Given the discrepancy in how PSMA PET was performed and reported, it questions the homogony of studies from centre to centre. Standardisation of PSMA PET is required for this to become a consistently useful and reproducible modality in the diagnosis of PCa.

Patient summary

Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) is being utilised for staging and localisation of prostate cancer (PCa); however, there is significant variability in performing and reporting PSMA PET. Standardisation of PSMA PET is required for results to be consistently useful and reproducible for the diagnosis of PCa.

The Impact of Peptide Amount on Tumor Uptake to Assess PSMA Receptor Saturation on 68Ga-PSMA-11 PET/CT in Patients with Primary Prostate Cancer

⁶⁸Ga-labeled prostate-specific membrane antigen (PSMA) is often produced on-site, where usually a fixed amount of peptide is conjugated to the generator eluate. However, fluctuations in specific activity might influence tracer distribution and tumor accumulation. Therefore, our aim was to investigate the potential effect of varying the administered peptide amount on ⁶⁸Ga-PSMA-11 uptake in tumors using PET/CT in patients with primary prostate cancer (PCa). Additionally, the impact of tumor volume on this potential effect and on accumulation in reference organs was assessed. Methods: The imaging data of 362 men with primary PCa who underwent ⁶⁸Ga-PSMA-11 PET/CT were retrospectively included. Scans were quantified for normal tissue and primary tumors. Patients were divided into 3 groups based on their tumor volume. Correlation and multivariable linear regression analyses were performed. Results: The median index lesion volume was 9.50 cm³ (range, 0.064-174 cm³). Groups were based on quartiles of prostatic lesion volume: ≤4.11 cm³ (group 1), 4.11-20.6 cm³ (group 2), and ≥20.6 cm³ (group 3). No correlation was found between administered peptide amount and tumor uptake (SUV_mean or SUV_peak) for any group, except for a significant correlation for SUV_mean in the first group (P = 0.008). Linear regression analysis supported these findings. Conclusion: The amount of administered peptide had no evident effect on ⁶⁸Ga-PSMA-11 uptake in tumors, except for a significant positive correlation between administered peptide amount and tumor SUV_mean for group 1. The findings imply that no receptor saturation occurs in men with primary PCa at peptide levels of about 2.5 μg.

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

BACKGROUND

High urinary activity in urinary bladder and ureters may hamper interpretation of prostate cancer and regional nodal metastases in prostate-specific membrane antigen (PSMA) PET/CT. The goal of this study was to assess effects of furosemide and choice of tracer on urinary activity in the bladder and ureters, as well as on occurrence of peri-bladder artefacts in PET/CT.

METHODS

Four cohorts with a total of 202 men staged with PSMA PET/CT for prostate cancer received either ⁶⁸Ga-PSMA-11 as tracer, with (cohort G+) or without 10mg intravenous furosemide (G-) concurrent with tracer, or ¹⁸F-DCFPyL with (F+) or without furosemide (F-). SUVmax of bladder and ureters, presence, type, and severity of peri-bladder artefacts were compared between cohorts. The influence of furosemide and choice of tracer was determined while taking differences in biodistribution time into account.

RESULTS

Median SUVmax bladder was 43,5; 14,8; 61,7 and 22,8 in cohorts G-, G+, F- and F+, respectively, resulting in significant overall (p < 0.001) and between cohort differences (p adjusted < 0.001 to 0.003) except between G- and F+. Median SUVmax ureter was 6.4; 4.5; 8.1 and 6.0 in cohorts G-, G+, F- and F+, respectively, resulting in significant overall (p < 0.001) and between cohort differences for G+ : F- and F- : F+ (p < 0.001, respectively, 0.019). Significant effects of furosemide and choice of tracer on SUVmax bladder (p < 0.001 resp. p = 0.001) and of furosemide on SUVmax ureter (p < 0.001) were found, whereas differences in biodistribution time had not impacted these results significantly. Peri-bladder artefacts were present in 42/202 (21%) patients and were significantly more frequent in the F- cohort, respectively, less frequent in the G+ cohort (p = 0.001 resp. p < 0.001). Peri-bladder artefacts had a direct positive correlation with SUVmax bladder (p = 0.033).

CONCLUSIONS

Increased urinary activity and higher incidence of peri-bladder artefacts were found in ¹⁸F-DCFPyL compared to ⁶⁸Ga-PSMA-11 PET/CT. Effective reduction of urinary activity may be reached through forced diuresis using 10mg intravenous furosemide, which is especially advantageous in ¹⁸F-DCFPyL PET/CT.

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

Rationale

PSMA-directed therapy for metastatic prostate cancer is gaining adoption as a treatment option. However, accumulation of ¹⁷⁷Lu/²²⁵Ac-PSMA in the salivary glands remains a problem, with risk of dose-limiting xerostomia and potentially severe effect on the quality of life. Gustatory stimulation is an approach that has commonly been used in radioactive iodine therapy to reduce accumulation in the salivary glands. However, based on theoretical differences in biodistribution, it was hypothesized that this could potentially lead to adverse increased toxicity for PSMA-ligand therapy. The primary objective of this work was to determine if gustatory stimulation by eating an assortment of sweet/fatty/acidic foods during the biodistribution phase of [¹⁸F]DCFPyl could result in a clinically relevant (> 30%) change in the uptake of the tracer in the salivary glands.

Methods

10 patients who already received a whole-body [¹⁸F]DCFPyl PET/CT scan for evaluation of prostate cancer, underwent a repeat (intervention) PET/CT scan within a month of the first (control) scan. During the intervention scan, patients chose from an assortment of sweet/fatty/acidic foods, which they then chewed and swallowed for a period of time starting 1 min before tracer administration to 10 min thereafter. Data from both scans were analyzed by placing VOIs on the major salivary glands and segmenting them using relative thresholds.

Results

A slight increase in PSMA uptake in the parotid glands was observed on the intervention scan when compared to the baseline scan (+ 7.1% SUL_mean and + 9.2% SUL_max, p < 0.05). No significant difference in PSMA uptake in the submandibular glands was seen.

Conclusions

Eating only slightly increases uptake of [¹⁸F]DCFPyl in the parotid glands. We nonetheless recommend refraining from gustatory stimulation during the administration and early biodistribution phase of radionuclide therapy with PSMA-ligands to reduce the risk of avoidable additional toxicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-021-00838-y.