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 [177Lu- DOTA0,Tyr3]octreotate. Some use octreotide as the peptide for peptide receptor radionuclide therapy (PRRT). We compared in seven patients [177Lu-DOTA0,Tyr3]octreotide ( 177Lu-DOTATOC) and [177Lu-DOTA0,Tyr 3]octreotate (177Lu-DOTATATE), to see which peptide should be preferred for PRRT with 177Lu. Methods: In the same patients, 3,700 MBq 177Lu-DOTATOC and 3,700 MBq 177Lu-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 177Lu-DOTATATE (p=0.016 in each case). Comparing 177Lu-DOTATATE with 177Lu-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 177Lu-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 177Lu-DOTATATE was comparable to that after 177Lu- DOTATOC. Urinary excretion of radioactivity was comparable during the first 6 h; thereafter there was a significant advantage for 177Lu-DOTATOC. Conclusion: 177Lu-DOTATATE had a longer tumour residence time than 177Lu-DOTATOC. Despite a longer residence time in kidneys after 177Lu-DOTATATE, tumour dose will always be higher. Therefore, we conclude that the better peptide for PRRT is octreotate.

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