Comparison of [177Lu-DOTA0, Tyr3] octreotate and [177Lu- DOTA0, Tyr3] octreotide:: which peptide is preferable for PRRT?

Purpose: Patients with somatostatin receptor subtype 2-positive metastasised neuroendocrine tumours can be treated with [Lu-177-DOTA(0), Tyr(3)] octreotate. Some use octreotide as the peptide for peptide receptor radionuclide therapy (PRRT). We compared in seven patients [Lu-177-DOTA(0), Tyr(3)] octreotide (Lu-177-DOTATOC) and [Lu-177-DOTA(0), Tyr(3)] octreotate (Lu-177-DOTATATE), to see which peptide should be preferred for PRRT with Lu-177. Methods: In the same patients, 3,700 MBq Lu-177-DOTATOC and 3,700 MBq Lu-177-DOTATATE was administered in separate therapy sessions. Amino acids were co-administered. Whole-body scanning was performed on days 1, 4 and 7 post therapy. Blood and urine samples were collected. We calculated residence times for tumours, spleen and kidneys. Results: All patients had longer residence times in spleen, kidneys and tumours after use of Lu-177-DOTATATE (p= 0.016 in each case). Comparing Lu-177-DOTATATE with Lu-177-DOTATOC, the mean residence time ratio was 2.1 for tumour, 1.5 for spleen and 1.4 for kidneys. Dose-limiting factors for PRRT are bone marrow and/or kidney dose. Although the residence time for kidneys was longer when using Lu-177-DOTATATE, the mean administered dose to tumours would still be advantageous by a factor of 1.5, assuming a fixed maximum kidney dose is reached. Plasma radioactivity after Lu-177-DOTATATE was comparable to that after Lu-177-DOTATOC. Urinary excretion of radioactivity was comparable during the first 6 h; thereafter there was a significant advantage for Lu-177-DOTATOC. Conclusion: Lu-177-DOTATATE had a longer tumour residence time than Lu-177-DOTATOC. Despite a longer residence time in kidneys after Lu-177-DOTATATE, tumour dose will always be higher. Therefore, we conclude that the better peptide for PRRT is octreotate.