PURPOSE: Patients with neuroendocrine neoplasms (NEN) engage in lifelong follow-up with frequent somatostatin receptor PET, e.g. [ 64Cu]Cu-DOTATATE PET, and continued measures to reduce radiation exposures should be in pursued in accordance with the as-low-as-reasonably-achievable (ALARA) principle. We therefore aimed to determine the lowest achievable [ 64Cu]Cu-DOTATATE dose while maintaining image quality and lesion detection rate.

PROCEDURES: We included scans from 38 patients with NEN referred to routine [ 64Cu]Cu-DOTATATE PET/CT. Using reconstruction of under-sampled PET list-mode data, we simulated [ 64Cu]Cu-DOTATATE activity dose-reduced PET equivalents with median [range] 142 MBq [127;157], 95 MBq [85;105], and 48 MBq [42;52], corresponding to 75% (PET 75%), 50% (PET 50%), and 25% (PET 25%) of the full-dose 191 MBq [169;209] (PET 100%). Three blinded readers independently assessed image quality (scores 1-5), lesion confidence (scores 0-2), and counted lesions grouped by organs and regions. Number of lesions, proportions of patients with diagnostic image quality (reader-median image quality ≥ 4), diagnostic lesion confidence (reader-median lesion confidence ≥ 1), and per-patient sensitivities and specificities for organ-specific disease on PET 75-25% were compared with PET 100%.

RESULTS: The median [ 64Cu]Cu-DOTATATE activity dose could be reduced from 191 to 142 MBq without decline in diagnostic image quality (P = 0.62), diagnostic lesion confidence (P = 1.0), or number of lesions detected in major organs or regions (P = 0.19-0.71). Sensitivity and specificity for detection of liver disease were 100% (26/26 patients) and 100% (12/12), respectively, for both PET 75% and PET 50%. Overall sensitivity for detection of NEN was 100% (26/26) for both PET 75% and PET 50%, and overall specificities were 92% (11/12) and 100% (12/12) for PET 75 and PET 50, respectively. Following dose-blinded post hoc review, the PET 75% specificity was adjusted to 100% (12/12).

CONCLUSIONS: The [ 64Cu]Cu-DOTATATE activity dose can be reduced from 191 MBq to at least 142 MBq without losing image quality or lesion detection ability and further reduced to 95 MBq without loss of clinically relevant information.