Head-to-Head Comparison between Peptide-Based Radiopharmaceutical for PET and SPECT in the Evaluation of Neuroendocrine Tumors: A Systematic Review

We compared head-to-head the most used radiolabeled peptides for single photon computed emission tomography (SPECT) and positron emission tomography (PET) imaging of neuroendocrine tumors (NETs). A comprehensive literature search was performed in PubMed, Web of Science, and Scopus databases. The following words, coupled two by two, were used: ⁶⁸Ga-DOTATOC; ⁶⁸Ga-DOTATATE; ⁶⁸Ga-DOTANOC; ^99mTc-EDDA/HYNIC-TOC; ⁶⁴Cu-DOTATATE; and ¹¹¹In-DTPA-octreotide. Moreover, a second-step search strategy was adopted by using the following combined terms: "Somatostatin receptor imaging,"; "Somatostatin receptor imaging" and "Functional,"; "Somatostatin receptor imaging" and "SPECT,"; and "Somatostatin receptor imaging" and "PET". Eligible criteria were: (1) original articles focusing on the clinical application of the radiopharmaceutical agents in NETs; (2) original articles in the English language; (3) comparative studies (head-to-head comparative or matched-paired studies). Editorials, letters to the editor, reviews, pictorial essays, clinical cases, or opinions were excluded. A total of 1077 articles were found in the three electronic databases. The full texts of 104 articles were assessed for eligibility. Nineteen articles were finally included. Most articles focused on the comparison between ¹¹¹In-DTPA-Octreotide and ⁶⁸Ga-DOTATOC/TATE. Few papers compared ⁶⁴Cu-DOTATATE and ⁶⁸Ga-DOTATOC/TATE, or SPECT tracers. The rates of true positivity were 63.7%, 58.5%, 78.4% and 82.4%, respectively, for ¹¹¹In-DTPA-Octreotide, ^99mTc-EDDA/HYNIC-TOC, ⁶⁸Ga-DOTATATE/TOC and ⁶⁴Cu-DOTATATE. In conclusion, as highly expected, PET tracers are more suitable for the in vivo identification of NETs. Indeed, in comparative studies, they demonstrated a higher true positive rate than SPECT agents.