Comparison of [18F]DOPA and [68Ga]DOTA-TOC as a PET imaging tracer before peptide receptor radionuclide therapy

Background In treatment of neuroendocrine neoplasms (NENs), confirmation of somatostatin receptor expression with 68 Ga-DOTA somatostatin analogues is mandatory to determine eligibility for peptide receptor radionuclide therapy (PRRT). [ 18 F]DOPA can detect additional lesions compared to [ 68 Ga]DOTA-TOC. The aim of this study was to explore differences in tumour detection of both tracers and their relevance for selecting patients for PRRT. We retrospectively studied eight patients with NENs who underwent both [ 68 Ga]DOTA-TOC and carbidopa-enhanced [ 18 F]DOPA PET/CT, before first-time PRRT with [ 177 Lu]DOTA-TATE. Tracer order was influenced due to stock availability or to detect suspected metastases with a second tracer. On CT, disease control was defined as a lesion showing complete response, partial response, or stable disease, according to RECIST 1.1. criteria. Results Seven patients with in total 89 lesions completed four infusions of 7.4 GBq [ 177 Lu]DOTA-TATE, one patient received only two cycles. Before treatment, [ 18 F]DOPA PET/CT detected significantly more lesions than [ 68 Ga]DOTA-TOC PET/CT (79 vs. 62, p