The efficacy of ¹⁷⁷Lu-DOTATATE in large neuroendocrine tumors (NETs) is reduced because of the lower energy (Eβmax 0.497 MeV) and shorter range of ¹⁷⁷Lu. The pure β-emitter ⁹⁰Y with its longer β range is more effective in larger tumors. This should be balanced with the greater risk of ⁹⁰Y-DOTATATE - related nephrotoxicity. Sequential duo - peptide receptor radionuclide therapy may result in a better response with minimal adverse effects in large-volume heterogeneous NETs. A 56-year-old man with large rectal NET liver metastases, treated with ⁹⁰Y-DOTATATE and ¹⁷⁷Lu-DOTATATE and sequential duo–peptide receptor radionuclide therapy, presented with post-⁹⁰Y-DOTATATE bremsstrahlung and PET/CT in comparison with ⁶⁸Ga-DOTATATE PET/CT and ¹⁷⁷Lu-DOTATATE scans.