Dose-reduced [18F]PSMA-1007 PET is feasible for functional imaging of the renal cortex

[18F]PSMA-1007 PET is comparable to [99mTc]Tc-DMSA SPECT for renal cortical imaging

BACKGROUND

Scintigraphy using technetium-99m labelled dimercaptosuccinic acid ([99mTc]Tc-DMSA), taken up in the proximal tubules, is the standard in functional imaging of the renal cortex. Recent guidelines recommend performing [99mTc]Tc-DMSA scintigraphy with single photon emission computed tomography (SPECT). Prostate-specific membrane antigen (PSMA) targeted positron emission tomography (PET) is used for staging and localization of recurrence in prostate cancer. A high renal uptake is often seen on PSMA PET, concordant with known PSMA expression in proximal tubules. This suggests PSMA PET could be used analogous to [99mTc]Tc-DMSA scintigraphy for renal cortical imaging. [18F]PSMA-1007 is a promising radiopharmaceutical for this purpose due to low urinary clearance. In this study, we aimed to compare [18F]PSMA-1007 PET to [99mTc]Tc-DMSA SPECT regarding split renal uptake and presence of renal uptake defects, in patients with prostate cancer. Three readers interpreted PET and SPECT images regarding presence of renal uptake defects, with each kidney split into cranial, mid and caudal segments. Kidneys were segmented in PET and SPECT images, and left renal uptake as a percentage of total renal uptake was measured.

RESULTS

Twenty patients with prostate cancer were included. 2 participants had single kidneys; thus 38 kidneys were evaluated. A total of 29 defects were found on both [99mTc]Tc-DMSA SPECT and [18F]PSMA-1007 PET. Cohen's kappa for concordance regarding presence of any defect was 0.76 on a per-segment basis and 0.67 on a per-kidney basis. Spearman's r for left renal uptake percentage between [99mTc]Tc-DMSA SPECT and [18F]PSMA-1007 PET was 0.95.

CONCLUSIONS

[18F]PSMA-1007 PET is comparable to [99mTc]Tc-DMSA SPECT for detection of uptake defects in this setting. Measurements of split renal function made using [18F]PSMA-1007 PET are valid and strongly correlated to measurements made with [99mTc]Tc-DMSA SPECT.

[18F]-PSMA-1007-PET for evaluation of kidney function

PURPOSE

Prostate-specific membrane antigen (PSMA) is present in the proximal tubule cells of the kidneys. This results in high renal tracer uptake in PSMA-PET, which may contain useful information on renal function. As part of the evaluation for [177Lu]-PSMA therapies, patients undergo PSMA-PET and additional [99mTc]-mercapto-acetyltriglycine (MAG3) scintigraphy to assess renal function. Aim of this study was to evaluate estimation of renal function with [18F]-PSMA-1007-PET/CT (PSMA-PET) by comparison to timely MAG3-scintigraphies.

MATERIALS AND METHODS

We retrospectively investigated 73 prostate cancer patients with 93 timely available PSMA-PET/CT, MAG3-scintigraphies and serum creatinine. For determination of split renal function in PSMA-PET/CT, we evaluated the relative unilateral total renal PSMA uptake, i.e. SUVmean multiplied by the renal volume (SRFPSMA-TOTAL) and relative unilateral maximal standardized uptake value (SRFSUV). These were compared to MAG3 split renal function (SRFMAG3) using Pearson correlation and receiver operating characteristics analysis. For determination of global renal function, correlation of bilateral total renal PSMA uptake with MAG3 tubular excretion rate and serum creatinine was assessed.

RESULTS

SRFMAG3 was strongly correlated with SRFPSMA-TOTAL (r= 0.872, p<0.001) and with SRFSUV (r=0.815, p<0.001). Relevant abnormalities of SRFMAG3 (unilateral renal function < 25 %) could be detected with sensitivities and specificities of 90% and 92% for SRFPSMA-TOTAL, and 80% and 95% for SRFSUV. Measures of absolute renal function were only weakly correlated with bilateral total renal PSMA uptake.

CONCLUSION

Renal [18F]-PSMA-1007 uptake allowed to quantify renal split function with good accuracy based on SRFPSMA-TOTAL or SRFSUV.

[18 F]PSMA-1007 renal uptake parameters: Reproducibility and relationship to estimated glomerular filtration rate

BACKGROUND

Scintigraphy with technetium-99m-labelled dimercaptosuccinic acid ([^99m Tc]Tc-DMSA) is widely used for renal cortical imaging. Uptake of [^99m Tc]Tc-DMSA has been shown to correlate with glomerular filtration rate (GFR). Prostate-specific membrane antigen (PSMA) radiopharmaceuticals used for positron emission tomography (PET) show high renal uptake and are being investigated for renal imaging. [⁶⁸ Ga]Ga-PSMA-11 PET parameters have been shown to correlate with estimated GFR (eGFR). The aim of this study was to investigate the relationship between renal [¹⁸ F]PSMA-1007 uptake and eGFR.

METHODS

Hundred and eighty-five patients underwent PET imaging at 1 and 2 h after injection of 4.0 ± 0.2 MBq [¹⁸ F]PSMA-1007. Serum creatinine levels were measured and GFR estimated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Modification of Diet in Renal Disease (MDRD) equations. Fifteen patients were excluded due to missing or incorrect data. Thus, data from 170 patients were analyzed. Kidneys were segmented in the PET images using a convolutional neural network with manual correction. For each kidney, mean standardized uptake value (SUV_mean ) and segmentation volume in millilitres were measured. Linear regression analyses were performed with eGFR as the outcome variable.

RESULTS

Variation in the eGFR values was explained to a significant degree by SUV_mean and renal segmentation volume in both the 1 and 2 h images. This correlation was stronger for CKD-EPI eGFR (1 h R²  = 0.64; 2 h R²  = 0.64) than for MDRD eGFR (1 h R²  = 0.47; 2 h R²  = 0.45).

CONCLUSION

Renal [¹⁸ F]PSMA-1007 uptake parameters correlate with eGFR and are indicative of renal cortical function.