A Comparison of 68 Ga-PSMA PET/CT-Based Split Renal Function with 99m Tc-MAG3 Renography in Patients with Metastatic Castration-Resistant Prostate Carcinoma Treated with 177 Lu-PSMA.

BACKGROUND: Physiological PSMA expression in the cells of the proximal renal tubules and consecutive radiopharmaceutical binding and retention could potentially lead to radioligand-therapy-induced nephrotoxicity. Thus, patients with metastatic castration-resistant prostate cancer undergo 99m Tc-Mercaptoacetyltriglycine (MAG3) renal scintigraphy to assess kidney function and to exclude renal obstruction as part of their workup for PSMA-targeted radioligand therapy (RLT). 99m Tc-MAG-3 renal scintigraphy often requires an additional visit to the nuclear medicine department and patients spend 30-90 min in the department, which is inconvenient and takes up camera time. In addition, the patients are subjected to a baseline 68 Ga-PSMA PET/CT to assess for PSMA-positive disease prior to targeted radioligand therapy. The aim of this retrospective cross-sectional study was to compare 99m Tc-MAG-3-based split renal function (SRF) with 68 Ga-PSMA-derived SRF.

METHODS: This retrospective cross-sectional study included 28 patients with histologically proven metastatic castration-resistant prostate cancer (mCRPC) who received 177Lu-PSMA617. A comparison between the split renal function using 68 Ga-PSMA PET/CT and the 99m Tc-MAG-3-derived split renal function was carried out in 56 kidneys ( n = 56). The SRF on 68 Ga-PSMA was calculated using the volume and the average standard uptake value (SUVmean) within each VOI calculated as previously described by Roser et al.: SRF = ( VOLUMEright ) ∗ SUVmeanright /( VOLUMEright ∗ SUVmeanright + VOLUMEleft ∗ SUVmeanleft ). Paired tests and correlation coefficients were used to compare 68 Ga-PSMA and 99m Tc-MAG-3. A visual comparison of kidney morphology on both studies was also performed.

RESULTS: The median SRF of the right kidney was 49.9% (range: 3-91%) using 68 Ga-PSMA PET/CT and 50.5% (range: 0-94%) with 99m Tc-MAG3 scintigraphy. Notably, there was a strong correlation between SRF measurements obtained from PSMA and 99m TcMAG3, with a Pearson correlation coefficient of 0.957 ( p < 0.001). Both 99m Tc-MAG3 and 68 Ga-PSMA PET/CT studies identified morphological renal abnormalities; there were nine hydronephrotic kidneys, four shrunken kidneys and one obstructed kidney, and there was a strong positive correlation between 68 Ga-PSMA kidney morphology and 99m TcMAG3 renal scintigraphy kidney morphology, with a correlation coefficient of 0.93.

CONCLUSIONS: PSMA-derived split function demonstrated a high correlation with renal function assessed on diuretic 99m Tc-MAG3 renograms. PET-derived split renal function may, therefore, be considered an alternative to diuretic renogram-based split function. Furthermore, both 99m Tc-MAG3 and 68 Ga-PSMA PET/CT studies identified morphological renal abnormalities such as hydronephrosis, shrunken and obstructed kidneys. This correlation underscores the potential utility of 68 Ga-PSMA imaging as a valuable tool for assessing kidney morphology as an alternative to renogram split function in clinical practice.