Impact of administered amount of peptide on tumor dosimetry at the first cycle of peptide receptor radionuclide therapy (PRRT) in relation to total tumor somatostatin receptor expression

BACKGROUND: The accumulation of (177)Lu-DOTATATE might be influenced by the amount of administered peptide in relation to the tumor somatostatin receptor expression. The effect of the administered peptide mass on the resulting absorbed dose in tumors and normal organs has not previously been assessed in relation to the patients’ tumor load. METHOD: Patients with small intestinal (n = 141) and pancreatic (n = 62) neuroendocrine tumors (NETs) who underwent PRRT were selected for retrospective evaluation. All patients had received 7.4 GBq (177)Lu-DOTATATE, and the amount of administered peptide in the preparation varied from 93 to 456 µg. The absorbed dose in tumors and normal tissue at the first PRRT cycle was calculated, based on SPECT-measurements at day 1, 4, and 7 post-infusion. The total tumor somatostatin receptor expression (tTSSTRE) was calculated on SPECT after 24 h by multiplying the functional tumor volume, delineated by 42% cut-off VOIs of the highest activity, with the SUVmean for the respective tumor VOIs. Spearman’s rank correlation analyzed any relationship between the administered amount of peptide and the absorbed dose in tumors and normal organs, in relation to the patients’ tTSSTRE. RESULTS: There was no correlation between the amount of peptide and any of the tested parameters in relation to tTSSTRE. CONCLUSION: In this retrospective analysis, no correlation between the amount of administered peptide in the (177)Lu-DOTATATE preparation and the absorbed radiation doses in tumors and normal tissues was demonstrated in relation to the total tumor SSTR expression.