First comparative dosimetric results after peptide receptor radionuclide therapy (PRRT) using Lu-177 DOTA-NOC and Lu-177 DOTA-TATE

1665 Objectives: DOTA-NOC, [DOTA]-1-Nal3-octreotide, a pansomatostatin analogue, shows high affinity to the somatostatin receptors (sstr) 3 and 5 and a very high affinity to sstr 2 which is predominant in neuroendocrine tumors. We compared uptake, half-life (kinetics) and mean absorbed organ and tumor doses of Lu-177 DOTA-NOC and Lu-177 DOTA-TATE. Methods: 126 patients with progressive neuroendocrine tumors with high sstr expression (verified by Ga-68 DOTA-NOC PET/CT) were studied. 118 patients (50m and 68f; aged 61±11a) were treated with 2.5-7.4 GBq Lu-177 DOTA-TATE and 8 patients (3m and 5f, aged 65±10a) with 3.6-7.4 GBq Lu-177 DOTA-NOC. Whole-body scans were performed after 0.5h, 3h, 24h, 48h, 72h and 96h p.i. Blood samples from 27 patients were obtained after therapy. By means of geometric mean and after background correction, ROI results were used to calculate the estimated absorbed organ and tumor doses (OLINDA software). Results: Lu-177 DOTA-NOC showed a higher uptake as compared to Lu-177 DOTA-TATE (=100%): for whole-body about 46% and in normal tissue 42%, in the spleen 26% and in the kidneys 22%. The tumor uptake was about 3% higher for DOTA-TATE. The effective half-life for whole-body was comparable for both peptides (t1/2a NOC 2.9h vs. TATE 2.4h and t1/2b NOC 56h vs. TATE 57h). In normal tissue, t1/2a was similar (NOC 2.6h; TATE 3.4h) but the t1/2b was longer for DOTA-TATE (NOC 43.9h; TATE 48.2h). t1/2b was longer for DOTA-NOC in the spleen (NOC 83h; TATE 72h) and in the kidney (NOC 71.2h; TATE 64.4h), the resulting mean absorbed doses in the kidney (NOC 6.5 Sv; TATE 4.6 Sv) and spleen (NOC 8.9 Sv; TATE 6.4 Sv) were higher for DOTA-NOC. In the tumor, the t1/2b was higher for both TATE (NOC 67h; TATE 78h). For DOTA-TATE the whole-body dose (0.27 Sv) was significant lower (t-test, p