The impact of ¹⁷⁷Lu-octreotide therapy on ^99mTc-MAG3 clearance is not predictive for late nephropathy

Peptide Receptor Radionuclide Therapy (PRRT) for the treatment of neuroendocrine tumors may lead to kidney deterioration. This study aimed to evaluate the suitability of ^99mTc-mercaptoacetyltriglycine (^99mTc- MAG3) clearance for the early detection of PRRT-induced changes on tubular extraction (TE). TE rate (TER) was measured prior to 128 PRRT cycles (7.6±0.4 GBq 177Lu-octreotate/octreotide each) in 32 patients. TER reduction during PRRT was corrected for age-related decrease and analyzed for the potential to predict loss of glomerular filtration (GF). The GF rate (GFR) as measure for renal function was derived from serum creatinine. The mean TER was 234 ± 53 ml/min/1.73 m² before PRRT (baseline) and 221 ± 45 ml/min/1.73 m² after a median follow-up of 370 days. The age-corrected decrease (mean: -3%, range: -27% to +19%) did not reach significance (p=0.09) but significantly correlated with the baseline TER (Spearman p=-0.62, p < 0.001). Patients with low baseline TER showed an improved TER after PRRT, high decreases were only observed in individuals with high baseline TER. Pre-therapeutic TER data were inferior to plasma creatininederived GFR estimates in predicting late nephropathy. TER assessed by ^99mTc-MAG3clearance prior to and during PRRT is not suitable as early predictor of renal injury and an increased risk for late nephropathy.