Additional Lesions Detected in Therapeutic Scans with 177Lu-DOTATATE Reflect Higher Affinity of 177Lu-DOTATATE for Somatostatin Receptors

Abstract

Objective: Peptide receptor-targeted radionuclide therapy (PRRT) of somatostatin receptor (SR)-expressing neuroendocrine tumors (NETs) has become an established therapeutic option in patients with advanced NETs. The aim of this study was to compare the lesion detection rate of ^99mTc-EDDA/HYNIC-TOC, a newly developed tracer for NET imaging, with ¹⁷⁷Lu-DOTATATE used for PRRT. Methods: 8 patients (4 women, 4 men, age range 46–76 years) with histologically proven NETs, who showed high SR loads by ^99mTc-EDDA/HYNIC-TOC scintigraphy, were treated with ¹⁷⁷Lu-DOTATATE. After treatment, all patients were subjected to whole-body scintigraphy with additional low-dose single-photon emission computed tomography (SPECT-CT) of the chest and abdomen. Results: All patients demonstrated ¹⁷⁷Lu-DOTATATE accumulation in all lesions previously detected by ^99mTc- EDDA/HYNIC-TOC scintigraphy. Three patients showed additional lesions in the liver and lungs. Conclusions: SPECT-CT after ¹⁷⁷Lu-DOTATATE therapy may be helpful in detecting additional lesions not seen using ^99mTc-EDDA/HYNIC-TOC. This could reflect the broader affinity of ¹⁷⁷Lu-DOTATATE for SRs compared with ^99mTc-EDDA/HYNIC-TOC.