Non-invasive estimation of split renal function from routine Ga-SSR-PET/CT scans.

Objective: Patients with impaired kidney function are at elevated risk for nephrotoxicity and hematotoxicity from peptide receptor radionuclide therapy (PPRT) for advanced neuroendocrine tumors. Somatostatin receptor (SSR)-PET/CT imaging is the method of choice to identify sufficient SSR expression as a prerequisite for PRRT. Therefore, our study aimed to explore whether split renal function could be evaluated using imaging data from routine SSR-PET/CT prior to PRRT.

Methods: In total, 25 consecutive patients who underwent SSR-PET/CT (Siemens Biograph mCT) before PRRT between June 2019 and December 2020 were enrolled in this retrospective study. PET acquisition in the caudocranial direction started at 20 ± 0.5 min after an i.v. injection of 173 ± 20 MBq [Ga]Ga-ha DOTATATE, and the kidneys were scanned at 32 ± 0.5 min p.i. The renal parenchyma was segmented semi-automatically using an SUV-based isocontour (SUV between 5 and 15). Multiple parameters including SUVmean of renal parenchyma and blood pool, as well as parenchyma volume, were extracted, and accumulation index (: renal parenchyma volume/SUVmean) and total kidney accumulation (: SUVmean x renal parenchyma volume) were calculated. All data were correlated with the reference standard tubular extraction rate (TER-MAG) from [Tc]Tc-MAG3 scintigraphy and glomerular filtration rate (GFR).

Results: SUVmean of the parenchymal tracer retention showed a negative correlation with TER (: -0.519, < 0.001) and GFR (: -0.555, < 0.001) at 32 min p.i. The herein-introduced ACI revealed a significant correlation ( < 0.05) with the total tubular function (: 0.482), glomerular renal function (: 0.461), split renal function (: 0.916), and absolute single-sided renal function (: 0.549). The mean difference between the split renal function determined by renal scintigraphy and ACI was 1.8 ± 4.2 % points.

Conclusion: This pilot study indicates that static [Ga]Ga-ha DOTATATE PET-scans at 32 min p.i. may be used to estimate both split renal function and absolute renal function using the herein proposed "Accumulation Index" (ACI).